Android 可拖拽的GridView效果实现, 长按可拖拽和item实时交换

转帖（http://blog.csdn.net/xiaanming/article/details/17718579）

在Android开发中，我们常常用到ListView和GridView，而有的时候系统的ListView，GridView并不能满足我们的需求，所以我们需要自己定义一个ListView或者GridView,我的上一篇文章中就是自定义的一个左右滑动删除item的例子，大家有兴趣的可以去看看 Android 使用Scroller实现绚丽的ListView左右滑动删除Item效果，今天这篇文章就给大家来自定义GridView的控件，GridView主要是来显示网格的控件，在Android的开发中使用很普通，相对于TextView，Button这些控件来说要来的复杂些，今天给大家带来长按GridView的item,然后将其拖拽其他item上面，使得GridView的item发生交换，比较典型的就是我们的Launcher，网上有很多关于GridView的拖动的Demo，但是大部分都是相同的，而且存在一些Bug,而且大部分都是点击GridView的item然后进行拖动，或者item之间不进行实时交换，今天给大家更加详细的介绍GridView拖拽，并且将Demo做的更完美，大家更容易接受，也许很多人听到这个感觉实现起来很复杂，就关掉的这篇文章，其实告诉大家，只要知道了思路就感觉一点都不复杂了，不信大家可以接着往下看看，首先还是跟大家说说实现的思路

根据手指按下的X,Y坐标来获取我们在GridView上面点击的item
手指按下的时候使用Handler和Runnable来实现一个定时器，假如定时时间为1000毫秒，在1000毫秒内，如果手指抬起了移除定时器，没有抬起并且手指点击在GridView的item所在的区域，则表示我们长按了GridView的item
如果我们长按了item则隐藏item,然后使用WindowManager来添加一个item的镜像在屏幕用来代替刚刚隐藏的item
当我们手指在屏幕移动的时候，更新item镜像的位置，然后在根据我们移动的X,Y的坐标来获取移动到GridView的哪一个位置
到GridView的item过多的时候，可能一屏幕显示不完，我们手指拖动item镜像到屏幕下方，要触发GridView想上滚动，同理，当我们手指拖动item镜像到屏幕上面，触发GridView向下滚动
GridView交换数据，刷新界面，移除item的镜像

看完上面的这些思路你是不是找到了些感觉了呢，心里痒痒的想动手试试吧，好吧，接下来就带大家根据思路来实现可拖拽的GridView，新建一个项目就叫DragGridView
新建一个类DragGridView继承GridView,先来看看DragGridView的代码，然后在根据代码进行相关的讲解

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- <span class="keyword">package</span> com.example.draggridview;

- 
- <span class="keyword">import</span> android.app.Activity;

- <span class="keyword">import</span> android.content.Context;

- <span class="keyword">import</span> android.graphics.Bitmap;

- <span class="keyword">import</span> android.graphics.PixelFormat;

- <span class="keyword">import</span> android.graphics.Rect;

- <span class="keyword">import</span> android.os.Handler;

- <span class="keyword">import</span> android.os.Vibrator;

- <span class="keyword">import</span> android.util.AttributeSet;

- <span class="keyword">import</span> android.view.Gravity;

- <span class="keyword">import</span> android.view.MotionEvent;

- <span class="keyword">import</span> android.view.View;

- <span class="keyword">import</span> android.view.WindowManager;

- <span class="keyword">import</span> android.widget.AdapterView;

- <span class="keyword">import</span> android.widget.GridView;

- <span class="keyword">import</span> android.widget.ImageView;

- 
- <span class="comment">/**</span>

- <span class="comment"> * @blog http://blog.csdn.net/xiaanming </span>

- <span class="comment"> * </span>

- <span class="comment"> * @author xiaanming</span>

- <span class="comment"> *</span>

- <span class="comment"> */</span>

- <span class="keyword">public</span> <span class="keyword">class</span> DragGridView <span class="keyword">extends</span> GridView{

- <span class="comment">/**</span>

- <span class="comment">     * DragGridView的item长按响应的时间， 默认是1000毫秒，也可以自行设置</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">long</span> dragResponseMS = <span class="number">1000</span>;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 是否可以拖拽，默认不可以</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">boolean</span> isDrag = <span class="keyword">false</span>;

- 
- <span class="keyword">private</span> <span class="keyword">int</span> mDownX;

- <span class="keyword">private</span> <span class="keyword">int</span> mDownY;

- <span class="keyword">private</span> <span class="keyword">int</span> moveX;

- <span class="keyword">private</span> <span class="keyword">int</span> moveY;

- <span class="comment">/**</span>

- <span class="comment">     * 正在拖拽的position</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mDragPosition;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 刚开始拖拽的item对应的View</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> View mStartDragItemView = <span class="keyword">null</span>;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 用于拖拽的镜像，这里直接用一个ImageView</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> ImageView mDragImageView;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 震动器</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> Vibrator mVibrator;

- 
- <span class="keyword">private</span> WindowManager mWindowManager;

- <span class="comment">/**</span>

- <span class="comment">     * item镜像的布局参数</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> WindowManager.LayoutParams mWindowLayoutParams;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 我们拖拽的item对应的Bitmap</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> Bitmap mDragBitmap;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 按下的点到所在item的上边缘的距离</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mPoint2ItemTop ;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 按下的点到所在item的左边缘的距离</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mPoint2ItemLeft;

- 
- <span class="comment">/**</span>

- <span class="comment">     * DragGridView距离屏幕顶部的偏移量</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mOffset2Top;

- 
- <span class="comment">/**</span>

- <span class="comment">     * DragGridView距离屏幕左边的偏移量</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mOffset2Left;

- 
- <span class="comment">/**</span>

- <span class="comment">     * 状态栏的高度</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mStatusHeight;

- 
- <span class="comment">/**</span>

- <span class="comment">     * DragGridView自动向下滚动的边界值</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mDownScrollBorder;

- 
- <span class="comment">/**</span>

- <span class="comment">     * DragGridView自动向上滚动的边界值</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">int</span> mUpScrollBorder;

- 
- <span class="comment">/**</span>

- <span class="comment">     * DragGridView自动滚动的速度</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">int</span> speed = <span class="number">20</span>;

- 
- <span class="comment">/**</span>

- <span class="comment">     * item发生变化回调的接口</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> OnChanageListener onChanageListener;

- 
- 
- 
- <span class="keyword">public</span> DragGridView(Context context) {

- <span class="keyword">this</span>(context, <span class="keyword">null</span>);

- }

- 
- <span class="keyword">public</span> DragGridView(Context context, AttributeSet attrs) {

- <span class="keyword">this</span>(context, attrs, <span class="number"></span>);

- }

- 
- <span class="keyword">public</span> DragGridView(Context context, AttributeSet attrs, <span class="keyword">int</span> defStyle) {

- <span class="keyword">super</span>(context, attrs, defStyle);

- mVibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);

- mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

- mStatusHeight = getStatusHeight(context); <span class="comment">//获取状态栏的高度</span>

- 
- }

- 
- <span class="keyword">private</span> Handler mHandler = <span class="keyword">new</span> Handler();

- 
- <span class="comment">//用来处理是否为长按的Runnable</span>

- <span class="keyword">private</span> Runnable mLongClickRunnable = <span class="keyword">new</span> Runnable() {

- 
- <span class="annotation">@Override</span>

- <span class="keyword">public</span> <span class="keyword">void</span> run() {

- isDrag = <span class="keyword">true</span>; <span class="comment">//设置可以拖拽</span>

- mVibrator.vibrate(<span class="number">50</span>); <span class="comment">//震动一下</span>

- mStartDragItemView.setVisibility(View.INVISIBLE);<span class="comment">//隐藏该item</span>

- 
- <span class="comment">//根据我们按下的点显示item镜像</span>

- createDragImage(mDragBitmap, mDownX, mDownY);

- }

- };

- 
- <span class="comment">/**</span>

- <span class="comment">     * 设置回调接口</span>

- <span class="comment">     * @param onChanageListener</span>

- <span class="comment">     */</span>

- <span class="keyword">public</span> <span class="keyword">void</span> setOnChangeListener(OnChanageListener onChanageListener){

- <span class="keyword">this</span>.onChanageListener = onChanageListener;

- }

- 
- <span class="comment">/**</span>

- <span class="comment">     * 设置响应拖拽的毫秒数，默认是1000毫秒</span>

- <span class="comment">     * @param dragResponseMS</span>

- <span class="comment">     */</span>

- <span class="keyword">public</span> <span class="keyword">void</span> setDragResponseMS(<span class="keyword">long</span> dragResponseMS) {

- <span class="keyword">this</span>.dragResponseMS = dragResponseMS;

- }

- 
- <span class="annotation">@Override</span>

- <span class="keyword">public</span> <span class="keyword">boolean</span> dispatchTouchEvent(MotionEvent ev) {

- <span class="keyword">switch</span>(ev.getAction()){

- <span class="keyword">case</span> MotionEvent.ACTION_DOWN:

- mDownX = (<span class="keyword">int</span>) ev.getX();

- mDownY = (<span class="keyword">int</span>) ev.getY();

- 
- <span class="comment">//根据按下的X,Y坐标获取所点击item的position</span>

- mDragPosition = pointToPosition(mDownX, mDownY);

- 
- 
- <span class="keyword">if</span>(mDragPosition == AdapterView.INVALID_POSITION){

- <span class="keyword">return</span> <span class="keyword">super</span>.dispatchTouchEvent(ev);

- }

- 
- <span class="comment">//使用Handler延迟dragResponseMS执行mLongClickRunnable</span>

- mHandler.postDelayed(mLongClickRunnable, dragResponseMS);

- 
- <span class="comment">//根据position获取该item所对应的View</span>

- mStartDragItemView = getChildAt(mDragPosition &#8211; getFirstVisiblePosition());

- 
- <span class="comment">//下面这几个距离大家可以参考我的博客上面的图来理解下</span>

- mPoint2ItemTop = mDownY &#8211; mStartDragItemView.getTop();

- mPoint2ItemLeft = mDownX &#8211; mStartDragItemView.getLeft();

- 
- mOffset2Top = (<span class="keyword">int</span>) (ev.getRawY() &#8211; mDownY);

- mOffset2Left = (<span class="keyword">int</span>) (ev.getRawX() &#8211; mDownX);

- 
- <span class="comment">//获取DragGridView自动向上滚动的偏移量，小于这个值，DragGridView向下滚动</span>

- mDownScrollBorder = getHeight() /<span class="number">4</span>;

- <span class="comment">//获取DragGridView自动向下滚动的偏移量，大于这个值，DragGridView向上滚动</span>

- mUpScrollBorder = getHeight() * <span class="number">3</span>/<span class="number">4</span>;

- 
- 
- 
- <span class="comment">//开启mDragItemView绘图缓存</span>

- mStartDragItemView.setDrawingCacheEnabled(<span class="keyword">true</span>);

- <span class="comment">//获取mDragItemView在缓存中的Bitmap对象</span>

- mDragBitmap = Bitmap.createBitmap(mStartDragItemView.getDrawingCache());

- <span class="comment">//这一步很关键，释放绘图缓存，避免出现重复的镜像</span>

- mStartDragItemView.destroyDrawingCache();

- 
- 
- <span class="keyword">break</span>;

- <span class="keyword">case</span> MotionEvent.ACTION_MOVE:

- <span class="keyword">int</span> moveX = (<span class="keyword">int</span>)ev.getX();

- <span class="keyword">int</span> moveY = (<span class="keyword">int</span>) ev.getY();

- 
- <span class="comment">//如果我们在按下的item上面移动，只要不超过item的边界我们就不移除mRunnable</span>

- <span class="keyword">if</span>(!isTouchInItem(mStartDragItemView, moveX, moveY)){

- mHandler.removeCallbacks(mLongClickRunnable);

- }

- <span class="keyword">break</span>;

- <span class="keyword">case</span> MotionEvent.ACTION_UP:

- mHandler.removeCallbacks(mLongClickRunnable);

- mHandler.removeCallbacks(mScrollRunnable);

- <span class="keyword">break</span>;

- }

- <span class="keyword">return</span> <span class="keyword">super</span>.dispatchTouchEvent(ev);

- }

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * 是否点击在GridView的item上面</span>

- <span class="comment">     * @param itemView</span>

- <span class="comment">     * @param x</span>

- <span class="comment">     * @param y</span>

- <span class="comment">     * @return</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">boolean</span> isTouchInItem(View dragView, <span class="keyword">int</span> x, <span class="keyword">int</span> y){

- <span class="keyword">if</span>(dragView == <span class="keyword">null</span>){

- <span class="keyword">return</span> <span class="keyword">false</span>;

- }

- <span class="keyword">int</span> leftOffset = dragView.getLeft();

- <span class="keyword">int</span> topOffset = dragView.getTop();

- <span class="keyword">if</span>(x < leftOffset || x > leftOffset + dragView.getWidth()){

- <span class="keyword">return</span> <span class="keyword">false</span>;

- }

- 
- <span class="keyword">if</span>(y < topOffset || y > topOffset + dragView.getHeight()){

- <span class="keyword">return</span> <span class="keyword">false</span>;

- }

- 
- <span class="keyword">return</span> <span class="keyword">true</span>;

- }

- 
- 
- 
- <span class="annotation">@Override</span>

- <span class="keyword">public</span> <span class="keyword">boolean</span> onTouchEvent(MotionEvent ev) {

- <span class="keyword">if</span>(isDrag && mDragImageView != <span class="keyword">null</span>){

- <span class="keyword">switch</span>(ev.getAction()){

- <span class="keyword">case</span> MotionEvent.ACTION_MOVE:

- moveX = (<span class="keyword">int</span>) ev.getX();

- moveY = (<span class="keyword">int</span>) ev.getY();

- <span class="comment">//拖动item</span>

- onDragItem(moveX, moveY);

- <span class="keyword">break</span>;

- <span class="keyword">case</span> MotionEvent.ACTION_UP:

- onStopDrag();

- isDrag = <span class="keyword">false</span>;

- <span class="keyword">break</span>;

- }

- <span class="keyword">return</span> <span class="keyword">true</span>;

- }

- <span class="keyword">return</span> <span class="keyword">super</span>.onTouchEvent(ev);

- }

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * 创建拖动的镜像</span>

- <span class="comment">     * @param bitmap </span>

- <span class="comment">     * @param downX</span>

- <span class="comment">     *          按下的点相对父控件的X坐标</span>

- <span class="comment">     * @param downY</span>

- <span class="comment">     *          按下的点相对父控件的X坐标</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">void</span> createDragImage(Bitmap bitmap, <span class="keyword">int</span> downX , <span class="keyword">int</span> downY){

- mWindowLayoutParams = <span class="keyword">new</span> WindowManager.LayoutParams();

- mWindowLayoutParams.format = PixelFormat.TRANSLUCENT; <span class="comment">//图片之外的其他地方透明</span>

- mWindowLayoutParams.gravity = Gravity.TOP | Gravity.LEFT;

- mWindowLayoutParams.x = downX &#8211; mPoint2ItemLeft + mOffset2Left;

- mWindowLayoutParams.y = downY &#8211; mPoint2ItemTop + mOffset2Top &#8211; mStatusHeight;

- mWindowLayoutParams.alpha = <span class="number"></span>.55f; <span class="comment">//透明度</span>

- mWindowLayoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;

- mWindowLayoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;

- mWindowLayoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE

- | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE ;

- 
- mDragImageView = <span class="keyword">new</span> ImageView(getContext());

- mDragImageView.setImageBitmap(bitmap);

- mWindowManager.addView(mDragImageView, mWindowLayoutParams);

- }

- 
- <span class="comment">/**</span>

- <span class="comment">     * 从界面上面移动拖动镜像</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">void</span> removeDragImage(){

- <span class="keyword">if</span>(mDragImageView != <span class="keyword">null</span>){

- mWindowManager.removeView(mDragImageView);

- mDragImageView = <span class="keyword">null</span>;

- }

- }

- 
- <span class="comment">/**</span>

- <span class="comment">     * 拖动item，在里面实现了item镜像的位置更新，item的相互交换以及GridView的自行滚动</span>

- <span class="comment">     * @param x</span>

- <span class="comment">     * @param y</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">void</span> onDragItem(<span class="keyword">int</span> moveX, <span class="keyword">int</span> moveY){

- mWindowLayoutParams.x = moveX &#8211; mPoint2ItemLeft + mOffset2Left;

- mWindowLayoutParams.y = moveY &#8211; mPoint2ItemTop + mOffset2Top &#8211; mStatusHeight;

- mWindowManager.updateViewLayout(mDragImageView, mWindowLayoutParams); <span class="comment">//更新镜像的位置</span>

- onSwapItem(moveX, moveY);

- 
- <span class="comment">//GridView自动滚动</span>

- mHandler.post(mScrollRunnable);

- }

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * 当moveY的值大于向上滚动的边界值，触发GridView自动向上滚动</span>

- <span class="comment">     * 当moveY的值小于向下滚动的边界值，触犯GridView自动向下滚动</span>

- <span class="comment">     * 否则不进行滚动</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> Runnable mScrollRunnable = <span class="keyword">new</span> Runnable() {

- 
- <span class="annotation">@Override</span>

- <span class="keyword">public</span> <span class="keyword">void</span> run() {

- <span class="keyword">int</span> scrollY;

- <span class="keyword">if</span>(moveY > mUpScrollBorder){

- scrollY = speed;

- mHandler.postDelayed(mScrollRunnable, <span class="number">25</span>);

- }<span class="keyword">else</span> <span class="keyword">if</span>(moveY < mDownScrollBorder){

- scrollY = -speed;

- mHandler.postDelayed(mScrollRunnable, <span class="number">25</span>);

- }<span class="keyword">else</span>{

- scrollY = <span class="number"></span>;

- mHandler.removeCallbacks(mScrollRunnable);

- }

- 
- <span class="comment">//当我们的手指到达GridView向上或者向下滚动的偏移量的时候，可能我们手指没有移动，但是DragGridView在自动的滚动</span>

- <span class="comment">//所以我们在这里调用下onSwapItem()方法来交换item</span>

- onSwapItem(moveX, moveY);

- 
- 
- smoothScrollBy(scrollY, <span class="number">10</span>);

- }

- };

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * 交换item,并且控制item之间的显示与隐藏效果</span>

- <span class="comment">     * @param moveX</span>

- <span class="comment">     * @param moveY</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">void</span> onSwapItem(<span class="keyword">int</span> moveX, <span class="keyword">int</span> moveY){

- <span class="comment">//获取我们手指移动到的那个item的position</span>

- <span class="keyword">int</span> tempPosition = pointToPosition(moveX, moveY);

- 
- <span class="comment">//假如tempPosition 改变了并且tempPosition不等于-1,则进行交换</span>

- <span class="keyword">if</span>(tempPosition != mDragPosition && tempPosition != AdapterView.INVALID_POSITION){

- <span class="keyword">if</span>(onChanageListener != <span class="keyword">null</span>){

- onChanageListener.onChange(mDragPosition, tempPosition);

- }

- 
- getChildAt(tempPosition &#8211; getFirstVisiblePosition()).setVisibility(View.INVISIBLE);<span class="comment">//拖动到了新的item,新的item隐藏掉</span>

- getChildAt(mDragPosition &#8211; getFirstVisiblePosition()).setVisibility(View.VISIBLE);<span class="comment">//之前的item显示出来</span>

- 
- mDragPosition = tempPosition;

- }

- }

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * 停止拖拽我们将之前隐藏的item显示出来，并将镜像移除</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">void</span> onStopDrag(){

- View view = getChildAt(mDragPosition &#8211; getFirstVisiblePosition());

- <span class="keyword">if</span>(view != <span class="keyword">null</span>){

- view.setVisibility(View.VISIBLE);

- }

- ((DragAdapter)<span class="keyword">this</span>.getAdapter()).setItemHide(-<span class="number">1</span>);

- removeDragImage();

- }

- 
- <span class="comment">/**</span>

- <span class="comment">     * 获取状态栏的高度</span>

- <span class="comment">     * @param context</span>

- <span class="comment">     * @return</span>

- <span class="comment">     */</span>

- <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">int</span> getStatusHeight(Context context){

- <span class="keyword">int</span> statusHeight = <span class="number"></span>;

- Rect localRect = <span class="keyword">new</span> Rect();

- ((Activity) context).getWindow().getDecorView().getWindowVisibleDisplayFrame(localRect);

- statusHeight = localRect.top;

- <span class="keyword">if</span> (<span class="number"></span> == statusHeight){

- Class<?> localClass;

- <span class="keyword">try</span> {

- localClass = Class.forName(<span class="string">&#8220;com.android.internal.R$dimen&#8221;</span>);

- Object localObject = localClass.newInstance();

- <span class="keyword">int</span> i5 = Integer.parseInt(localClass.getField(<span class="string">&#8220;status_bar_height&#8221;</span>).get(localObject).toString());

- statusHeight = context.getResources().getDimensionPixelSize(i5);

- } <span class="keyword">catch</span> (Exception e) {

- e.printStackTrace();

- }

- }

- <span class="keyword">return</span> statusHeight;

- }

- 
- 
- <span class="comment">/**</span>

- <span class="comment">     * </span>

- <span class="comment">     * @author xiaanming</span>

- <span class="comment">     *</span>

- <span class="comment">     */</span>

- <span class="keyword">public</span> <span class="keyword">interface</span> OnChanageListener{

- 
- <span class="comment">/**</span>

- <span class="comment">         * 当item交换位置的时候回调的方法，我们只需要在该方法中实现数据的交换即可</span>

- <span class="comment">         * @param form</span>

- <span class="comment">         *          开始的position</span>

- <span class="comment">         * @param to </span>

- <span class="comment">         *          拖拽到的position</span>

- <span class="comment">         */</span>

- <span class="keyword">public</span> <span class="keyword">void</span> onChange(<span class="keyword">int</span> form, <span class="keyword">int</span> to);

- }

- }

首先看DragGridView的事件分发方法，不了解Android事件分发的可以先去了解下，Android事件分发对于自定义控件很重要，简单说下，当我们点击DragGridView的Item,先会去执行dispatchTouchEvent()方法将事件分发下去，所以我们要重写dispatchTouchEvent()方法在手指按下的时候根据pointToPosition()方法来获取我们按下的item的position,根据getChildAt()方法来获取该position上面所对应的View, 并且开启长按的定时器，默认时间为1000毫秒，如果在1000毫秒内手指抬起或者手指在屏幕上滑动出了该item，则取消长按定时器，否则就表示可以进行拖拽，手机友好的震动一下，隐藏我们长按的Item，屏幕调用createDragImage()方法来创建我们长按的item的镜像，创建Item的镜像使用的是WindowManager类，该类可以创建一个窗体显示在Activity之上，再此之前大家先要理解这几个距离，理解这几个距离之前要首先知道getRawX(),getRawY()和getX(),getY()的区别，getRawX(),getRawY()是相对于屏幕的原点的距离，而getX(),getY()是相对于控件左上方的点的距离，为了方便大家理解我用Word简单的画了下图，画得不好，大家将就的看下，红色框框为我们的GridView

mPoint2ItemTop 手指按下的点到该Item的上边缘的距离，如上图的1号线
mPoint2ItemLeft 手指按下的点到该Item的左边缘的距离，如上图的2号线
mOffset2Top DragGridView的上边缘到屏幕上边缘的距离，如上图的3号线，这个距离包裹状态栏，标题栏，或者一些在DragGridView上面的布局的高度，这个很重要我们现实Item镜像需要用到
mOffset2Left DragGridView的左边缘到屏幕左边缘的距离，如上图的4号线，我这个Demo的这个距离为0，因为我设置DragGridView的宽度为充满屏幕，但是我们要考虑假如DragGridView与屏幕左边缘设置了间隙或者左边有其他的布局的情形
mDownScrollBorder 这个距离表示当DragGridView的item过多的时候，手机一屏显示不完全，我们拖动Item镜像到这个高度的时候，DragGridView自动向下滚动，如上图的5号线
.mUpScrollBorder 这个和mDownScrollBorder相反，当我们大于这个高度的时候，DragGridView自动向上滚动，如上图的6号线

理解了这六个距离，我们就来看看创建Item镜像的方法里面，其他的我不多说，首先设置format为PixelFormat.TRANSLUCENT，表示除了我们显示图片和文字的其他地方为透明，之后就是x，y这两个距离的计算，计算的是item的左上角的坐标，理解了上面这六个距离我们很容易得出x,y的坐标，可是你会发现y的坐标减去了状态栏的高度，这点大家需要注意下，另外我们需要获取item的绘制缓存的Bitmap对象，然后将Bitmap设置到一个ImageView上面，为什么要这么做呢？如果调用addView()方法将item 直接添加到WindowManager里面，会有异常产生，因为item已经有了自己归属的父容器DragGridView，所有我们这里使用一个ImageView来代替item添加到WindowManager里面

上面已经完成了开始拖拽的准备工作，要想拖动镜像我们还需要重写onTouchEvent()方法，获取移动的X,Y的坐标，利用WindowManager的updateViewLayout方法就能对镜像进行拖动，拖动的镜像的时候为了有更好的用户体验，我们还要做item的实时交换效果，我们利用手指移动的X,Y坐标，利用pointToPosition()来获取拖拽到的position,然后将之前的item显示出来，将拖拽到的item进行隐藏，这样子就完成了item在界面上面的交换，但是数据交换我这里没有做，所以我提供了回调接口OnChanageListener，我们只需要自己实现数据的交换逻辑然后刷新DragGridView即可，我们还需要实现DragGridView的自动向上滚动或者向下滚动，使用Handler和mScrollRunnable利用smoothScrollToPositionFromTop()来实现DragGridView滚动，具体的实现大家可以看代码

手指离开界面，将item的镜像移除，并将拖拽到的item显示出来，这样子就实现了GirdView的拖拽效果啦，接下来我们来使用下我们自定义可拖拽的GridView吧，先看主界面布局，只有我们自定义的一个DragGridView

**[html]** [view plain](http://blog.csdn.net/xiaanming/article/details/17718579#)[copy](http://blog.csdn.net/xiaanming/article/details/17718579#)[![在CODE上查看代码片](https://code.csdn.net/assets/CODE_ico.png)](https://code.csdn.net/snippets/143802)[![派生到我的代码片](https://code.csdn.net/assets/ico_fork.svg)](https://code.csdn.net/snippets/143802/fork)

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  - <span class="tag"><</span><span class="tag-name">RelativeLayout</span> <span class="attribute">xmlns:android</span>=<span class="attribute-value">&#8220;http://schemas.android.com/apk/res/android&#8221;</span>
  
  - <span class="attribute">xmlns:tools</span>=<span class="attribute-value">&#8220;http://schemas.android.com/tools&#8221;</span>
  
  - <span class="attribute">android:layout_width</span>=<span class="attribute-value">&#8220;match_parent&#8221;</span>
  
  - <span class="attribute">android:layout_height</span>=<span class="attribute-value">&#8220;match_parent&#8221;</span> <span class="tag">></span>
  
  - 
  - <span class="tag"><</span><span class="tag-name">com.example.draggridview.DragGridView</span>
  
  - <span class="attribute">android:id</span>=<span class="attribute-value">&#8220;@+id/dragGridView&#8221;</span>
  
  - <span class="attribute">android:listSelector</span>=<span class="attribute-value">&#8220;@android:color/transparent&#8221;</span>
  
  - <span class="attribute">android:layout_width</span>=<span class="attribute-value">&#8220;match_parent&#8221;</span>
  
  - <span class="attribute">android:layout_height</span>=<span class="attribute-value">&#8220;match_parent&#8221;</span>
  
  - <span class="attribute">android:cacheColorHint</span>=<span class="attribute-value">&#8220;@android:color/transparent&#8221;</span>
  
  - <span class="attribute">android:verticalSpacing</span>=<span class="attribute-value">&#8220;10dip&#8221;</span>
  
  - <span class="attribute">android:horizontalSpacing</span>=<span class="attribute-value">&#8220;10dip&#8221;</span>
  
  - <span class="attribute">android:stretchMode</span>=<span class="attribute-value">&#8220;columnWidth&#8221;</span>
  
  - <span class="attribute">android:gravity</span>=<span class="attribute-value">&#8220;center&#8221;</span>
  
  - <span class="attribute">android:numColumns</span>=<span class="attribute-value">&#8220;3&#8221;</span> <span class="tag">></span>
  
  - <span class="tag"></</span><span class="tag-name">com.example.draggridview.DragGridView</span><span class="tag">></span>
  
  - 
  - <span class="tag"></</span><span class="tag-name">RelativeLayout</span><span class="tag">></span>

接下来我们看看DragGridView的item的布局，上面一个ImageView下面一个TextView

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  - <span class="tag"><?</span><span class="tag-name">xml</span> <span class="attribute">version</span>=<span class="attribute-value">&#8220;1.0&#8221;</span> <span class="attribute">encoding</span>=<span class="attribute-value">&#8220;utf-8&#8221;</span><span class="tag">?></span>
  
  - <span class="tag"><</span><span class="tag-name">RelativeLayout</span> <span class="attribute">xmlns:android</span>=<span class="attribute-value">&#8220;http://schemas.android.com/apk/res/android&#8221;</span>
  
  - <span class="attribute">android:layout_width</span>=<span class="attribute-value">&#8220;fill_parent&#8221;</span>
  
  - <span class="attribute">android:layout_height</span>=<span class="attribute-value">&#8220;wrap_content&#8221;</span>
  
  - <span class="attribute">android:background</span>=<span class="attribute-value">&#8220;@android:color/transparent&#8221;</span> <span class="tag">></span>
  
  - 
  - <span class="tag"><</span><span class="tag-name">ImageView</span>
  
  - <span class="attribute">android:id</span>=<span class="attribute-value">&#8220;@+id/item_image&#8221;</span>
  
  - <span class="attribute">android:scaleType</span>=<span class="attribute-value">&#8220;centerCrop&#8221;</span>
  
  - <span class="attribute">android:layout_width</span>=<span class="attribute-value">&#8220;wrap_content&#8221;</span>
  
  - <span class="attribute">android:layout_height</span>=<span class="attribute-value">&#8220;wrap_content&#8221;</span>
  
  - <span class="attribute">android:layout_centerHorizontal</span>=<span class="attribute-value">&#8220;true&#8221;</span> <span class="tag">></span>
  
  - <span class="tag"></</span><span class="tag-name">ImageView</span><span class="tag">></span>
  
  - 
  - <span class="tag"><</span><span class="tag-name">TextView</span>
  
  - <span class="attribute">android:id</span>=<span class="attribute-value">&#8220;@+id/item_text&#8221;</span>
  
  - <span class="attribute">android:layout_width</span>=<span class="attribute-value">&#8220;wrap_content&#8221;</span>
  
  - <span class="attribute">android:layout_height</span>=<span class="attribute-value">&#8220;wrap_content&#8221;</span>
  
  - <span class="attribute">android:layout_below</span>=<span class="attribute-value">&#8220;@+id/item_image&#8221;</span>
  
  - <span class="attribute">android:layout_centerHorizontal</span>=<span class="attribute-value">&#8220;true&#8221;</span> <span class="tag">></span>
  
  - <span class="tag"></</span><span class="tag-name">TextView</span><span class="tag">></span>
  
  - 
  - <span class="tag"></</span><span class="tag-name">RelativeLayout</span><span class="tag">></span>

布局搞定了我们就来看看主页面MainActivity的代码吧

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  - <span class="keyword">package</span> com.example.draggridview;
  
  - 
  - <span class="keyword">import</span> java.util.ArrayList;
  
  - <span class="keyword">import</span> java.util.Collections;
  
  - <span class="keyword">import</span> java.util.HashMap;
  
  - <span class="keyword">import</span> java.util.List;
  
  - 
  - <span class="keyword">import</span> android.app.Activity;
  
  - <span class="keyword">import</span> android.os.Bundle;
  
  - <span class="keyword">import</span> android.widget.SimpleAdapter;
  
  - 
  - <span class="keyword">import</span> com.example.draggridview.DragGridView.OnChanageListener;
  
  - 
  - <span class="comment">/**</span>
  
  - <span class="comment"> * @blog http://blog.csdn.net/xiaanming </span>
  
  - <span class="comment"> * </span>
  
  - <span class="comment"> * @author xiaanming</span>
  
  - <span class="comment"> *</span>
  
  - <span class="comment"> */</span>
  
  - <span class="keyword">public</span> <span class="keyword">class</span> MainActivity <span class="keyword">extends</span> Activity {
  
  - <span class="keyword">private</span> List<HashMap<String, Object>> dataSourceList = <span class="keyword">new</span> ArrayList<HashMap<String, Object>>();
  
  - 
  - <span class="annotation">@Override</span>
  
  - <span class="keyword">protected</span> <span class="keyword">void</span> onCreate(Bundle savedInstanceState) {
  
  - <span class="keyword">super</span>.onCreate(savedInstanceState);
  
  - setContentView(R.layout.activity_main);
  
  - 
  - DragGridView mDragGridView = (DragGridView) findViewById(R.id.dragGridView);
  
  - <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number"></span>; i < <span class="number">30</span>; i++) {
  
  - HashMap<String, Object> itemHashMap = <span class="keyword">new</span> HashMap<String, Object>();
  
  - itemHashMap.put(<span class="string">&#8220;item_image&#8221;</span>,R.drawable.com_tencent_open_notice_msg_icon_big);
  
  - itemHashMap.put(<span class="string">&#8220;item_text&#8221;</span>, <span class="string">&#8220;拖拽 &#8220;</span> + Integer.toString(i));
  
  - dataSourceList.add(itemHashMap);
  
  - }
  
  - 
  - 
  - <span class="keyword">final</span> SimpleAdapter mSimpleAdapter = <span class="keyword">new</span> SimpleAdapter(<span class="keyword">this</span>, dataSourceList,
  
  - R.layout.grid_item, <span class="keyword">new</span> String[] { <span class="string">&#8220;item_image&#8221;</span>, <span class="string">&#8220;item_text&#8221;</span> },
  
  - <span class="keyword">new</span> <span class="keyword">int</span>[] { R.id.item_image, R.id.item_text });
  
  - 
  - mDragGridView.setAdapter(mSimpleAdapter);
  
  - 
  - mDragGridView.setOnChangeListener(<span class="keyword">new</span> OnChanageListener() {
  
  - 
  - <span class="annotation">@Override</span>
  
  - <span class="keyword">public</span> <span class="keyword">void</span> onChange(<span class="keyword">int</span> from, <span class="keyword">int</span> to) {
  
  - HashMap<String, Object> temp = dataSourceList.get(from);
  
  - <span class="comment">//直接交互item</span>
  
  - <span class="comment">//              dataSourceList.set(from, dataSourceList.get(to));</span>
  
  - <span class="comment">//              dataSourceList.set(to, temp);</span>
  
  - <span class="comment">//              dataSourceList.set(to, temp);</span>
  
  - 
  - 
  - <span class="comment">//这里的处理需要注意下</span>
  
  - <span class="keyword">if</span>(from < to){
  
  - <span class="keyword">for</span>(<span class="keyword">int</span> i=from; i<to; i++){
  
  - Collections.swap(dataSourceList, i, i+<span class="number">1</span>);
  
  - }
  
  - }<span class="keyword">else</span> <span class="keyword">if</span>(from > to){
  
  - <span class="keyword">for</span>(<span class="keyword">int</span> i=from; i>to; i&#8211;){
  
  - Collections.swap(dataSourceList, i, i-<span class="number">1</span>);
  
  - }
  
  - }
  
  - 
  - dataSourceList.set(to, temp);
  
  - 
  - mSimpleAdapter.notifyDataSetChanged();
  
  - 
  - 
  - }
  
  - });
  
  - 
  - }
  
  - 
  - }

这里面的代码还是比较简单，主要讲下onChange()方法，我们要为mDragGridView设置一个OnChanageListener的回调接口，在onChange()方法里面实现数据的交换逻辑，第一个参数from为item开始的位置，第二个参数to为item拖拽到的位置，刚开始我使用的交换逻辑是

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  - HashMap<String, Object> temp = dataSourceList.get(from);
  
  - <span class="comment">//直接交互item</span>
  
  - <span class="comment">//              dataSourceList.set(from, dataSourceList.get(to));</span>
  
  - <span class="comment">//              dataSourceList.set(to, temp);</span>

直接交换的item的数据，然后看了下网易新闻的拖拽的GridView，他不是直接实现两个item直接的数据交换，所以将数据交换逻辑改成了下面的方式

简单说下，数据的交换逻辑，比如我们将position从5拖拽到7这个位置，我注释掉的逻辑是直接将5和7的数据交换，而后面的那种逻辑是将6的位置数据移动到5，将7的位置移动到6，然后再7显示5 6->5, 7->6, 5->7不知道大家理解了没有。

接下来我们来运行下项目，在运行之前我们不要忘了在AndroidManifest.xml里面加入震动的权限

![](http://img.blog.csdn.net/20131231174313125)

好了，今天的讲解就到此结束，效果还不错吧，看完这篇文章你是不是觉得GridView拖拽也不是那么难实现呢？你心里是不是也大概有自己的一个思路，建议大家自己敲敲看看，可以自己去实现下ListView的拖拽实现，ListView比GridView简单些，好的学习方法不是看得懂人家的代码，而是看完代码自己根据脑海里的思路自己敲出来，所以还是鼓励大家多敲代码，不明白的同学在下面留言，我会为大家解答的！

[项目源码，点击下载](http://download.csdn.net/detail/xiaanming/6812885)

PS:上面的代码在4.0以上的机器上面运行是OK的，但是在4.0以下的机器存在几个问题，首先是兼容性的问题，首先smoothScrollToPositionFromTop()方法在2.x的机器是不存在的，但是我们可以使用smoothScrollBy()来代替上面的方法使得GridView滚动

注意：很多朋友说运行在2.3的机器上面拖动的时候出现某些item无缘无故的隐藏了，笔者在写demo的时候一直用的是4.0的真机运行的，后面博主使用模拟器运行在2.3的机器上面，确实存在很多朋友反应的问题，原因就是因为博主使用的是SimpleAdapter，SimpleAdapter会复用Item，所以才导致本不该隐藏的item隐藏了，但是为什么运行在博主4.0的机器上面不出现问题，博主也很纳闷，现在我对其做出了修改，采用自定义Adapter，对item不采用复用的原则，虽然效率上面有点点不足，但是如果对于item不多的GridView，效率不足可以忽略，新修改的代码可以运行在2.X以上的机器不出现朋友们所说的问题了，并且添加了Item的移动动画效果，非常感谢大家提出的问题！

[添加item交换动画，点击下载](http://download.csdn.net/detail/xiaanming/7302793)

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