Android 高清加载巨图方案 拒绝压缩图片

转载请标明出处：http://blog.csdn.net/lmj623565791/article/details/49300989；

一、概述

距离上一篇博客有段时间没更新了，主要是最近有些私事导致的，那么就先来一篇简单一点的博客脉动回来。

对于加载图片，大家都不陌生，一般为了尽可能避免OOM都会按照如下做法：

1. 对于图片显示：根据需要显示图片控件的大小对图片进行压缩显示。
2. 如果图片数量非常多：则会使用LruCache等缓存机制，将所有图片占据的内容维持在一个范围内。

其实对于图片加载还有种情况，就是单个图片非常巨大，并且还不允许压缩。比如显示：世界地图、清明上河图、微博长图等。

那么对于这种需求，该如何做呢？

首先不压缩，按照原图尺寸加载，那么屏幕肯定是不够大的，并且考虑到内存的情况，不可能一次性整图加载到内存中，所以肯定是局部加载，那么就需要用到一个类：

• BitmapRegionDecoder

其次，既然屏幕显示不完，那么最起码要添加一个上下左右拖动的手势，让用户可以拖动查看。

那么综上，本篇博文的目的就是去自定义一个显示巨图的View，支持用户去拖动查看，大概的效果图如下：

好吧，这清明上河图太长了，想要观看全图，文末下载，图片在assets目录。当然如果你的图，高度也很大，肯定也是可以上下拖动的。

二、初识BitmapRegionDecoder

BitmapRegionDecoder主要用于显示图片的某一块矩形区域，如果你需要显示某个图片的指定区域，那么这个类非常合适。

对于该类的用法，非常简单，既然是显示图片的某一块区域，那么至少只需要一个方法去设置图片；一个方法传入显示的区域即可；详见：

• BitmapRegionDecoder提供了一系列的newInstance方法来构造对象，支持传入文件路径，文件描述符，文件的inputstrem等。例如： ``` BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder.newInstance(inputStream, <span class="hljs-keyword">false</span>);

  * 上述解决了传入我们需要处理的图片，那么接下来就是显示指定的区域。 ```
`bitmapRegionDecoder.decodeRegion(rect, options);`

参数一很明显是一个rect，参数二是BitmapFactory.Options，你可以控制图片的`inSampleSize`,`inPreferredConfig`等。  

那么下面看一个超级简单的例子：

```

`<span class=“hljs-keyword”>package</span> com.zhy.blogcodes.largeImage;

<span class=“hljs-keyword”>import</span> android.graphics.Bitmap; <span class=“hljs-keyword”>import</span> android.graphics.BitmapFactory; <span class=“hljs-keyword”>import</span> android.graphics.BitmapRegionDecoder; <span class=“hljs-keyword”>import</span> android.graphics.Rect; <span class=“hljs-keyword”>import</span> android.os.Bundle; <span class=“hljs-keyword”>import</span> android.support.v7.app.AppCompatActivity; <span class=“hljs-keyword”>import</span> android.widget.ImageView;

<span class=“hljs-keyword”>import</span> com.zhy.blogcodes.R;

<span class=“hljs-keyword”>import</span> java.io.IOException; <span class=“hljs-keyword”>import</span> java.io.InputStream;

<span class=“hljs-keyword”>public</span> <span class=“hljs-class”><span class=“hljs-keyword”>class</span> <span class=“hljs-title”>LargeImageViewActivity</span> <span class=“hljs-keyword”>extends</span> <span class=“hljs-title”>AppCompatActivity</span> {</span> <span class=“hljs-keyword”>private</span> ImageView mImageView;

<span class="hljs-annotation">@Override</span>
<span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>(Bundle savedInstanceState)
{
    <span class="hljs-keyword">super</span>.onCreate(savedInstanceState);
    setContentView(R.layout.activity_large_image_view);

    mImageView = (ImageView) findViewById(R.id.id_imageview);
    <span class="hljs-keyword">try</span>
    {
        InputStream inputStream = getAssets().open(<span class="hljs-string">"tangyan.jpg"</span>);

        <span class="hljs-comment">//获得图片的宽、高</span>
        BitmapFactory.Options tmpOptions = <span class="hljs-keyword">new</span> BitmapFactory.Options();
        tmpOptions.inJustDecodeBounds = <span class="hljs-keyword">true</span>;
        BitmapFactory.decodeStream(inputStream, <span class="hljs-keyword">null</span>, tmpOptions);
        <span class="hljs-keyword">int</span> width = tmpOptions.outWidth;
        <span class="hljs-keyword">int</span> height = tmpOptions.outHeight;

        <span class="hljs-comment">//设置显示图片的中心区域</span>
        BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder.newInstance(inputStream, <span class="hljs-keyword">false</span>);
        BitmapFactory.Options options = <span class="hljs-keyword">new</span> BitmapFactory.Options();
        options.inPreferredConfig = Bitmap.Config.RGB_565;
        Bitmap bitmap = bitmapRegionDecoder.decodeRegion(<span class="hljs-keyword">new</span> Rect(width / <span class="hljs-number">2</span> - <span class="hljs-number">100</span>, height / <span class="hljs-number">2</span> - <span class="hljs-number">100</span>, width / <span class="hljs-number">2</span> + <span class="hljs-number">100</span>, height / <span class="hljs-number">2</span> + <span class="hljs-number">100</span>), options);
        mImageView.setImageBitmap(bitmap);


    } <span class="hljs-keyword">catch</span> (IOException e)
    {
        e.printStackTrace();
    }


}

}`

    
    上述代码，就是使用BitmapRegionDecoder去加载assets中的图片，调用`bitmapRegionDecoder.decodeRegion`解析图片的中间矩形区域，返回bitmap，最终显示在ImageView上。
    
    效果图：
    
![](http://img.blog.csdn.net/20151021103048017) 
    
    上面的小图显示的即为下面的大图的中间区域。
    
    ok，那么目前我们已经了解了`BitmapRegionDecoder`的基本用户，那么往外扩散，我们需要自定义一个控件去显示巨图就很简单了，首先Rect的范围就是我们View的大小，然后根据用户的移动手势，不断去更新我们的Rect的参数即可。
    
    ## <a name="t3"></a>三、自定义显示大图控件 {#三自定义显示大图控件}
    
    根据上面的分析呢，我们这个自定义控件思路就非常清晰了：
    
      * 提供一个设置图片的入口
      * 重写onTouchEvent，在里面根据用户移动的手势，去更新显示区域的参数
      * 每次更新区域参数后，调用invalidate，onDraw里面去regionDecoder.decodeRegion拿到bitmap，去draw
    
    理清了，发现so easy，下面上代码：
    
    ```
`&lt;span class="hljs-keyword">package&lt;/span> com.zhy.blogcodes.largeImage.view;

&lt;span class="hljs-keyword">import&lt;/span> android.content.Context;
&lt;span class="hljs-keyword">import&lt;/span> android.graphics.Bitmap;
&lt;span class="hljs-keyword">import&lt;/span> android.graphics.BitmapFactory;
&lt;span class="hljs-keyword">import&lt;/span> android.graphics.BitmapRegionDecoder;
&lt;span class="hljs-keyword">import&lt;/span> android.graphics.Canvas;
&lt;span class="hljs-keyword">import&lt;/span> android.graphics.Rect;
&lt;span class="hljs-keyword">import&lt;/span> android.util.AttributeSet;
&lt;span class="hljs-keyword">import&lt;/span> android.view.MotionEvent;
&lt;span class="hljs-keyword">import&lt;/span> android.view.View;

&lt;span class="hljs-keyword">import&lt;/span> java.io.IOException;
&lt;span class="hljs-keyword">import&lt;/span> java.io.InputStream;

&lt;span class="hljs-javadoc">/**
 * Created by zhy on 15/5/16.
 */&lt;/span>
&lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-class">&lt;span class="hljs-keyword">class&lt;/span> &lt;span class="hljs-title">LargeImageView&lt;/span> &lt;span class="hljs-keyword">extends&lt;/span> &lt;span class="hljs-title">View&lt;/span>
{&lt;/span>
    &lt;span class="hljs-keyword">private&lt;/span> BitmapRegionDecoder mDecoder;
    &lt;span class="hljs-javadoc">/**
     * 图片的宽度和高度
     */&lt;/span>
    &lt;span class="hljs-keyword">private&lt;/span> &lt;span class="hljs-keyword">int&lt;/span> mImageWidth, mImageHeight;
    &lt;span class="hljs-javadoc">/**
     * 绘制的区域
     */&lt;/span>
    &lt;span class="hljs-keyword">private&lt;/span> &lt;span class="hljs-keyword">volatile&lt;/span> Rect mRect = &lt;span class="hljs-keyword">new&lt;/span> Rect();

    &lt;span class="hljs-keyword">private&lt;/span> MoveGestureDetector mDetector;


    &lt;span class="hljs-keyword">private&lt;/span> &lt;span class="hljs-keyword">static&lt;/span> &lt;span class="hljs-keyword">final&lt;/span> BitmapFactory.Options options = &lt;span class="hljs-keyword">new&lt;/span> BitmapFactory.Options();

    &lt;span class="hljs-keyword">static&lt;/span>
    {
        options.inPreferredConfig = Bitmap.Config.RGB_565;
    }

    &lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">setInputStream&lt;/span>(InputStream is)
    {
        &lt;span class="hljs-keyword">try&lt;/span>
        {
            mDecoder = BitmapRegionDecoder.newInstance(is, &lt;span class="hljs-keyword">false&lt;/span>);
            BitmapFactory.Options tmpOptions = &lt;span class="hljs-keyword">new&lt;/span> BitmapFactory.Options();
            &lt;span class="hljs-comment">// Grab the bounds for the scene dimensions&lt;/span>
            tmpOptions.inJustDecodeBounds = &lt;span class="hljs-keyword">true&lt;/span>;
            BitmapFactory.decodeStream(is, &lt;span class="hljs-keyword">null&lt;/span>, tmpOptions);
            mImageWidth = tmpOptions.outWidth;
            mImageHeight = tmpOptions.outHeight;

            requestLayout();
            invalidate();
        } &lt;span class="hljs-keyword">catch&lt;/span> (IOException e)
        {
            e.printStackTrace();
        } &lt;span class="hljs-keyword">finally&lt;/span>
        {

            &lt;span class="hljs-keyword">try&lt;/span>
            {
                &lt;span class="hljs-keyword">if&lt;/span> (is != &lt;span class="hljs-keyword">null&lt;/span>) is.close();
            } &lt;span class="hljs-keyword">catch&lt;/span> (Exception e)
            {
            }
        }
    }


    &lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">init&lt;/span>()
    {
        mDetector = &lt;span class="hljs-keyword">new&lt;/span> MoveGestureDetector(getContext(), &lt;span class="hljs-keyword">new&lt;/span> MoveGestureDetector.SimpleMoveGestureDetector()
        {
            &lt;span class="hljs-annotation">@Override&lt;/span>
            &lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-keyword">boolean&lt;/span> &lt;span class="hljs-title">onMove&lt;/span>(MoveGestureDetector detector)
            {
                &lt;span class="hljs-keyword">int&lt;/span> moveX = (&lt;span class="hljs-keyword">int&lt;/span>) detector.getMoveX();
                &lt;span class="hljs-keyword">int&lt;/span> moveY = (&lt;span class="hljs-keyword">int&lt;/span>) detector.getMoveY();

                &lt;span class="hljs-keyword">if&lt;/span> (mImageWidth &gt; getWidth())
                {
                    mRect.offset(-moveX, &lt;span class="hljs-number">0&lt;/span>);
                    checkWidth();
                    invalidate();
                }
                &lt;span class="hljs-keyword">if&lt;/span> (mImageHeight &gt; getHeight())
                {
                    mRect.offset(&lt;span class="hljs-number">0&lt;/span>, -moveY);
                    checkHeight();
                    invalidate();
                }

                &lt;span class="hljs-keyword">return&lt;/span> &lt;span class="hljs-keyword">true&lt;/span>;
            }
        });
    }


    &lt;span class="hljs-keyword">private&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">checkWidth&lt;/span>()
    {


        Rect rect = mRect;
        &lt;span class="hljs-keyword">int&lt;/span> imageWidth = mImageWidth;
        &lt;span class="hljs-keyword">int&lt;/span> imageHeight = mImageHeight;

        &lt;span class="hljs-keyword">if&lt;/span> (rect.right &gt; imageWidth)
        {
            rect.right = imageWidth;
            rect.left = imageWidth - getWidth();
        }

        &lt;span class="hljs-keyword">if&lt;/span> (rect.left &lt; &lt;span class="hljs-number">0&lt;/span>)
        {
            rect.left = &lt;span class="hljs-number">0&lt;/span>;
            rect.right = getWidth();
        }
    }


    &lt;span class="hljs-keyword">private&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">checkHeight&lt;/span>()
    {

        Rect rect = mRect;
        &lt;span class="hljs-keyword">int&lt;/span> imageWidth = mImageWidth;
        &lt;span class="hljs-keyword">int&lt;/span> imageHeight = mImageHeight;

        &lt;span class="hljs-keyword">if&lt;/span> (rect.bottom &gt; imageHeight)
        {
            rect.bottom = imageHeight;
            rect.top = imageHeight - getHeight();
        }

        &lt;span class="hljs-keyword">if&lt;/span> (rect.top &lt; &lt;span class="hljs-number">0&lt;/span>)
        {
            rect.top = &lt;span class="hljs-number">0&lt;/span>;
            rect.bottom = getHeight();
        }
    }


    &lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-title">LargeImageView&lt;/span>(Context context, AttributeSet attrs)
    {
        &lt;span class="hljs-keyword">super&lt;/span>(context, attrs);
        init();
    }

    &lt;span class="hljs-annotation">@Override&lt;/span>
    &lt;span class="hljs-keyword">public&lt;/span> &lt;span class="hljs-keyword">boolean&lt;/span> &lt;span class="hljs-title">onTouchEvent&lt;/span>(MotionEvent event)
    {
        mDetector.onToucEvent(event);
        &lt;span class="hljs-keyword">return&lt;/span> &lt;span class="hljs-keyword">true&lt;/span>;
    }

    &lt;span class="hljs-annotation">@Override&lt;/span>
    &lt;span class="hljs-keyword">protected&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">onDraw&lt;/span>(Canvas canvas)
    {
        Bitmap bm = mDecoder.decodeRegion(mRect, options);
        canvas.drawBitmap(bm, &lt;span class="hljs-number">0&lt;/span>, &lt;span class="hljs-number">0&lt;/span>, &lt;span class="hljs-keyword">null&lt;/span>);
    }

    &lt;span class="hljs-annotation">@Override&lt;/span>
    &lt;span class="hljs-keyword">protected&lt;/span> &lt;span class="hljs-keyword">void&lt;/span> &lt;span class="hljs-title">onMeasure&lt;/span>(&lt;span class="hljs-keyword">int&lt;/span> widthMeasureSpec, &lt;span class="hljs-keyword">int&lt;/span> heightMeasureSpec)
    {
        &lt;span class="hljs-keyword">super&lt;/span>.onMeasure(widthMeasureSpec, heightMeasureSpec);

        &lt;span class="hljs-keyword">int&lt;/span> width = getMeasuredWidth();
        &lt;span class="hljs-keyword">int&lt;/span> height = getMeasuredHeight();

        &lt;span class="hljs-keyword">int&lt;/span> imageWidth = mImageWidth;
        &lt;span class="hljs-keyword">int&lt;/span> imageHeight = mImageHeight;

         &lt;span class="hljs-comment">//默认直接显示图片的中心区域，可以自己去调节&lt;/span>
        mRect.left = imageWidth / &lt;span class="hljs-number">2&lt;/span> - width / &lt;span class="hljs-number">2&lt;/span>;
        mRect.top = imageHeight / &lt;span class="hljs-number">2&lt;/span> - height / &lt;span class="hljs-number">2&lt;/span>;
        mRect.right = mRect.left + width;
        mRect.bottom = mRect.top + height;

    }


}`

根据上述源码:

  1. setInputStream里面去获得图片的真实的宽度和高度，以及初始化我们的mDecoder
  2. onMeasure里面为我们的显示区域的rect赋值，大小为view的尺寸
  3. onTouchEvent里面我们监听move的手势，在监听的回调里面去改变rect的参数，以及做边界检查，最后invalidate
  4. 在onDraw里面就是根据rect拿到bitmap，然后draw了

ok，上面并不复杂，不过大家有没有注意到，这个监听用户move手势的代码写的有点奇怪，恩，这里模仿了系统的`ScaleGestureDetector`，编写了`MoveGestureDetector`，代码如下：

  * MoveGestureDetector ```

` <span class=“hljs-keyword”>package</span> com.zhy.blogcodes.largeImage.view;

<span class=“hljs-keyword”>import</span> android.content.Context; <span class=“hljs-keyword”>import</span> android.graphics.PointF; <span class=“hljs-keyword”>import</span> android.view.MotionEvent;

<span class=“hljs-keyword”>public</span> <span class=“hljs-class”><span class=“hljs-keyword”>class</span> <span class=“hljs-title”>MoveGestureDetector</span> <span class=“hljs-keyword”>extends</span> <span class=“hljs-title”>BaseGestureDetector</span> {</span>

<span class="hljs-keyword">private</span> PointF mCurrentPointer;
<span class="hljs-keyword">private</span> PointF mPrePointer;
<span class="hljs-comment">//仅仅为了减少创建内存</span>
<span class="hljs-keyword">private</span> PointF mDeltaPointer = <span class="hljs-keyword">new</span> PointF();

<span class="hljs-comment">//用于记录最终结果，并返回</span>
<span class="hljs-keyword">private</span> PointF mExtenalPointer = <span class="hljs-keyword">new</span> PointF();

<span class="hljs-keyword">private</span> OnMoveGestureListener mListenter;


<span class="hljs-keyword">public</span> <span class="hljs-title">MoveGestureDetector</span>(Context context, OnMoveGestureListener listener)
{
    <span class="hljs-keyword">super</span>(context);
    mListenter = listener;
}

<span class="hljs-annotation">@Override</span>
<span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleInProgressEvent</span>(MotionEvent event)
{
    <span class="hljs-keyword">int</span> actionCode = event.getAction() & MotionEvent.ACTION_MASK;
    <span class="hljs-keyword">switch</span> (actionCode)
    {
        <span class="hljs-keyword">case</span> MotionEvent.ACTION_CANCEL:
        <span class="hljs-keyword">case</span> MotionEvent.ACTION_UP:
            mListenter.onMoveEnd(<span class="hljs-keyword">this</span>);
            resetState();
            <span class="hljs-keyword">break</span>;
        <span class="hljs-keyword">case</span> MotionEvent.ACTION_MOVE:
            updateStateByEvent(event);
            <span class="hljs-keyword">boolean</span> update = mListenter.onMove(<span class="hljs-keyword">this</span>);
            <span class="hljs-keyword">if</span> (update)
            {
                mPreMotionEvent.recycle();
                mPreMotionEvent = MotionEvent.obtain(event);
            }
            <span class="hljs-keyword">break</span>;

    }
}

<span class="hljs-annotation">@Override</span>
<span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleStartProgressEvent</span>(MotionEvent event)
{
    <span class="hljs-keyword">int</span> actionCode = event.getAction() & MotionEvent.ACTION_MASK;
    <span class="hljs-keyword">switch</span> (actionCode)
    {
        <span class="hljs-keyword">case</span> MotionEvent.ACTION_DOWN:
            resetState();<span class="hljs-comment">//防止没有接收到CANCEL or UP ,保险起见</span>
            mPreMotionEvent = MotionEvent.obtain(event);
            updateStateByEvent(event);
            <span class="hljs-keyword">break</span>;
        <span class="hljs-keyword">case</span> MotionEvent.ACTION_MOVE:
            mGestureInProgress = mListenter.onMoveBegin(<span class="hljs-keyword">this</span>);
            <span class="hljs-keyword">break</span>;
    }

}

<span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">updateStateByEvent</span>(MotionEvent event)
{
    <span class="hljs-keyword">final</span> MotionEvent prev = mPreMotionEvent;

    mPrePointer = caculateFocalPointer(prev);
    mCurrentPointer = caculateFocalPointer(event);

    <span class="hljs-comment">//Log.e("TAG", mPrePointer.toString() + " ,  " + mCurrentPointer);</span>

    <span class="hljs-keyword">boolean</span> mSkipThisMoveEvent = prev.getPointerCount() != event.getPointerCount();

    <span class="hljs-comment">//Log.e("TAG", "mSkipThisMoveEvent = " + mSkipThisMoveEvent);</span>
    mExtenalPointer.x = mSkipThisMoveEvent ? <span class="hljs-number">0</span> : mCurrentPointer.x - mPrePointer.x;
    mExtenalPointer.y = mSkipThisMoveEvent ? <span class="hljs-number">0</span> : mCurrentPointer.y - mPrePointer.y;

}

<span class="hljs-javadoc">/**
 * 根据event计算多指中心点
 *
 *<span class="hljs-javadoctag"> @param</span> event
 *<span class="hljs-javadoctag"> @return</span>
 */</span>
<span class="hljs-keyword">private</span> PointF <span class="hljs-title">caculateFocalPointer</span>(MotionEvent event)
{
    <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> count = event.getPointerCount();
    <span class="hljs-keyword">float</span> x = <span class="hljs-number">0</span>, y = <span class="hljs-number">0</span>;
    <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i < count; i++)
    {
        x += event.getX(i);
        y += event.getY(i);
    }

    x /= count;
    y /= count;

    <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> PointF(x, y);
}


<span class="hljs-keyword">public</span> <span class="hljs-keyword">float</span> <span class="hljs-title">getMoveX</span>()
{
    <span class="hljs-keyword">return</span> mExtenalPointer.x;

}

<span class="hljs-keyword">public</span> <span class="hljs-keyword">float</span> <span class="hljs-title">getMoveY</span>()
{
    <span class="hljs-keyword">return</span> mExtenalPointer.y;
}


<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">OnMoveGestureListener</span>
{</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">onMoveBegin</span>(MoveGestureDetector detector);

    <span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">onMove</span>(MoveGestureDetector detector);

    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onMoveEnd</span>(MoveGestureDetector detector);
}

<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">SimpleMoveGestureDetector</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">OnMoveGestureListener</span>
{</span>

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">onMoveBegin</span>(MoveGestureDetector detector)
    {
        <span class="hljs-keyword">return</span> <span class="hljs-keyword">true</span>;
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">onMove</span>(MoveGestureDetector detector)
    {
        <span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>;
    }

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onMoveEnd</span>(MoveGestureDetector detector)
    {
    }
}

}`

    
      * BaseGestureDetector ```
`package com.zhy.blogcodes.largeImage.view;

import android.content.Context;
import android.view.MotionEvent;


<span class="hljs-keyword">public</span> <span class="hljs-keyword">abstract</span> <span class="hljs-keyword">class</span> BaseGestureDetector
{

    <span class="hljs-keyword">protected</span> boolean mGestureInProgress;

    <span class="hljs-keyword">protected</span> MotionEvent mPreMotionEvent;
    <span class="hljs-keyword">protected</span> MotionEvent mCurrentMotionEvent;

    <span class="hljs-keyword">protected</span> Context mContext;

    <span class="hljs-keyword">public</span> <span class="hljs-title">BaseGestureDetector</span>(Context context)
    {
        mContext = context;
    }


    <span class="hljs-keyword">public</span> boolean <span class="hljs-title">onToucEvent</span>(MotionEvent <span class="hljs-keyword">event</span>)
    {

        <span class="hljs-keyword">if</span> (!mGestureInProgress)
        {
            handleStartProgressEvent(<span class="hljs-keyword">event</span>);
        } <span class="hljs-keyword">else</span>
        {
            handleInProgressEvent(<span class="hljs-keyword">event</span>);
        }

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

    }

    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">abstract</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleInProgressEvent</span>(MotionEvent <span class="hljs-keyword">event</span>);

    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">abstract</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleStartProgressEvent</span>(MotionEvent <span class="hljs-keyword">event</span>);

    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">abstract</span> <span class="hljs-keyword">void</span> <span class="hljs-title">updateStateByEvent</span>(MotionEvent <span class="hljs-keyword">event</span>);

    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">resetState</span>()
    {
        <span class="hljs-keyword">if</span> (mPreMotionEvent != <span class="hljs-keyword">null</span>)
        {
            mPreMotionEvent.recycle();
            mPreMotionEvent = <span class="hljs-keyword">null</span>;
        }
        <span class="hljs-keyword">if</span> (mCurrentMotionEvent != <span class="hljs-keyword">null</span>)
        {
            mCurrentMotionEvent.recycle();
            mCurrentMotionEvent = <span class="hljs-keyword">null</span>;
        }
        mGestureInProgress = <span class="hljs-keyword">false</span>;
    }


}`

    你可能会说，一个move手势搞这么多代码，太麻烦了。的确是的，move手势的检测非常简单，那么之所以这么写呢，主要是为了可以复用，比如现在有一堆的`XXXGestureDetector`，当我们需要监听什么手势，就直接拿个detector来检测多方便。我相信大家肯定也郁闷过Google，为什么只有`ScaleGestureDetector`而没有`RotateGestureDetector`呢。  
    
    根据上述，大家应该理解了为什么要这么做，当时不强制，每个人都有个性。
    
    > 不过值得一提的是：上面这个手势检测的写法，不是我想的，而是一个开源的项目<https://github.com/rharter/android-gesture-detectors>，里面包含很多的手势检测。对应的博文是：<http://code.almeros.com/android-multitouch-gesture-detectors#.VibzzhArJXg>那面上面两个类就是我偷学了的~ 哈
    
    ## <a name="t4"></a>四、测试 {#四测试}
    
    测试其实没撒好说的了，就是把我们的LargeImageView放入布局文件，然后Activity里面去设置inputstream了。
    
    ```

`<span class=“hljs-tag”><<span class=“hljs-title”>RelativeLayout</span> <span class=“hljs-attribute”>xmlns:android</span>=<span class=“hljs-value”>“http://schemas.android.com/apk/res/android"&lt;/span> <span class=“hljs-attribute”>xmlns:tools</span>=<span class=“hljs-value”>“http://schemas.android.com/tools"&lt;/span> <span class=“hljs-attribute”>android:layout_width</span>=<span class=“hljs-value”>“match_parent”</span> <span class=“hljs-attribute”>android:layout_height</span>=<span class=“hljs-value”>“match_parent”</span>></span>

<span class="hljs-tag"><<span class="hljs-title">com.zhy.blogcodes.largeImage.view.LargeImageView

</span> <span class=“hljs-attribute”>android:id</span>=<span class=“hljs-value”>”@+id/id_largetImageview”</span> <span class=“hljs-attribute”>android:layout_width</span>=<span class=“hljs-value”>“match_parent”</span> <span class=“hljs-attribute”>android:layout_height</span>=<span class=“hljs-value”>“match_parent”</span>/></span>

<span class=“hljs-tag”></<span class=“hljs-title”>RelativeLayout</span>></span>`

        
        然后在Activity里面去设置图片：
        
        ```
`<span class="hljs-keyword">package</span> com.zhy.blogcodes.largeImage;

<span class="hljs-keyword">import</span> android.os.Bundle;
<span class="hljs-keyword">import</span> android.support.v7.app.AppCompatActivity;

<span class="hljs-keyword">import</span> com.zhy.blogcodes.R;
<span class="hljs-keyword">import</span> com.zhy.blogcodes.largeImage.view.LargeImageView;

<span class="hljs-keyword">import</span> java.io.IOException;
<span class="hljs-keyword">import</span> java.io.InputStream;

<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">LargeImageViewActivity</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">AppCompatActivity</span>
{</span>
    <span class="hljs-keyword">private</span> LargeImageView mLargeImageView;

    <span class="hljs-annotation">@Override</span>
    <span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onCreate</span>(Bundle savedInstanceState)
    {
        <span class="hljs-keyword">super</span>.onCreate(savedInstanceState);
        setContentView(R.layout.activity_large_image_view);

        mLargeImageView = (LargeImageView) findViewById(R.id.id_largetImageview);
        <span class="hljs-keyword">try</span>
        {
            InputStream inputStream = getAssets().open(<span class="hljs-string">"world.jpg"</span>);
            mLargeImageView.setInputStream(inputStream);

        } <span class="hljs-keyword">catch</span> (IOException e)
        {
            e.printStackTrace();
        }


    }

}`

    效果图：

    ok，那么到此，显示巨图的方案以及详细的代码就描述完成了，总体还是非常简单的。  
    但是，在实际的项目中，可能会有更多的需求，比如增加放大、缩小；增加快滑手势等等，那么大家可以去参考这个库：<https://github.com/johnnylambada/WorldMap>，该库基本实现了绝大多数的需求，大家根据本文这个思路再去看这个库，也会简单很多，定制起来也容易。我这个地图的图就是该库里面提供的。
    
    哈，掌握了这个，以后面试过程中也可以悄悄的装一把了，当你优雅的答完android加载图片的方案以后，然后接一句，其实还有一种情况，就是高清显示巨图，那么我们应该…相信面试官对你的印象会好很多~ have a nice day ~
    
    [源码点击下载][1]
    
    * * *
    
    ## <a name="t5"></a>参考链接 {#参考链接}
    
      * <http://code.almeros.com/android-multitouch-gesture-detectors#.VibzzhArJXg>
      * <https://github.com/rharter/android-gesture-detectors>
      * <https://github.com/johnnylambada/WorldMap>