LargeImageView超大图的显示Demo
对于加载图片，一般为了尽可能避免OOM都会按照如下做法：
- 对于图片显示：根据显示图片的控件大小对图片进行压缩；
- 对于图片数量非常多：使用LruCache等缓存机制，将一些图片维持在内存中；
其实对于图片还有一种加载情况，就是单个图片非常巨大且不允许压缩。比如显示：世界地图，清明上河图... 那么对于这种需求该如何实现？ 首先不压缩，按照原图尺寸加载，那么屏幕肯定不够大，所以肯定是局部加载，那么肯定用到一个类：
BitmapRegionRecoder其次，既然屏幕显示不完全，就需要添加Move手势检查，让用户可以拖动查看。
#BitmapRegionRecoder简单使用 BitmapRegionRecoder主要用于显示图片的某一块矩形区域。 BitmapRegionDecoder提供一系列构造方法来初始化该对象，支持传入文件路径，文件描述符，文件的inputstream等。 例如：
BitmapRegionDecoder bitmapRegionDecoder =
BitmapRegionDecoder.newInstance(inputStream, false);接下来就是显示指定区域的方法：
bitmapRegionDecoder.decodeRegion(rect, options);参数一是一个rect，参数二是BitmapFactory.Options,可以控制inSampleSize,inPreferredConfig等。
思路：
- 提供一个设置图片的入口
- 重写onTouchEvent()方法，根据用户移动的手势，去更新显示区域的Rect
- 每次更新Rect之后，调用invalidate方法，重写onDraw(),在里面去regionDecoder.decodeRegion(rect, options)实现绘制
上代码：
public class LargeImageView extends View
{
/**
* BitmapRegionDecoder
*/
private BitmapRegionDecoder mDecoder;
private static final BitmapFactory.Options mDecodeOptions = new BitmapFactory.Options();
static
{
mDecodeOptions.inPreferredConfig = Bitmap.Config.RGB_565;
}
private Rect mRect = new Rect();
//图片的宽高
private int mImageWidth;
private int mImageHeight;
//检测Move
private MoveGestureDetector mMoveGestureDetector;
public LargeImageView(Context context, AttributeSet attrs)
{
super(context, attrs);
init();
}
/**
* 对外公布的方法，设置图片
*
* @param is
*/
public void getImageInputStream(InputStream is)
{
try
{
//初始化mDecoder
mDecoder = BitmapRegionDecoder.newInstance(is, false);
//得到图片的宽高
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, options);
mImageWidth = options.outWidth;
mImageHeight = options.outHeight;
requestLayout();
invalidate();
} catch (IOException e)
{
e.printStackTrace();
}finally
{
try
{
if(is != null)
{
is.close();
}
}catch (Exception e)
{}
}
}
private void init()
{
mMoveGestureDetector = new MoveGestureDetector(getContext(),
new MoveGestureDetector.SimpleMoveGestureDetector()
{
@Override
public boolean onMove(MoveGestureDetector detector)
{
//移动rect
int movX = (int) detector.getMoveX();
int movY = (int) detector.getMoveY();
if(mImageWidth > getWidth())
{
mRect.offset(-movX, 0);
checkWidth();
invalidate();
}
if(mImageHeight > getHeight())
{
mRect.offset(0, -movY);
checkHeight();
invalidate();
}
return true;
}
});
}
private void checkHeight()
{
if(mRect.bottom > mImageHeight)
{
mRect.bottom = mImageHeight;
mRect.top = mRect.bottom - getHeight();
}
if(mRect.top < 0)
{
mRect.top = 0;
mRect.bottom = mRect.top + getHeight();
}
}
private void checkWidth()
{
if(mRect.right > mImageWidth)
{
mRect.right = mImageWidth;
mRect.left = mImageWidth - getWidth();
}
if(mRect.left < 0)
{
mRect.left = 0;
mRect.right = mRect.left + getWidth();
}
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
mMoveGestureDetector.onTouchEvent(event);
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int width = getMeasuredWidth();
int height = getMeasuredHeight();
//初始化mRect，显示图片中间区域
mRect.left = mImageWidth/2 - width/2;
mRect.top = mImageHeight/2 - height/2;
mRect.right = mRect.left + width;
mRect.bottom = mRect.top + height;
}
@Override
protected void onDraw(Canvas canvas)
{
//拿到最新rect对应的bitmap，进行绘制；
Bitmap bitmap = mDecoder.decodeRegion(mRect, mDecodeOptions);
canvas.drawBitmap(bitmap, 0, 0, null);
}
}根据上述代码
- getImageInputStream里面获取图片的真实高度，初始化mDecoder
- onMeasure里面初始化mRect，大小为view的尺寸，并且显示图片中间区域
- onTouchEvent里面监听Move手势，在监听的回调里面改变Rect参数，以及边界检查，最后invalidate
- onDraw里面拿到最新rect对应的bitmap，进行绘制
OK，上面并不复杂；但是监听Move的方法有点奇怪：
mMoveGestureDetector.onTouchEvent(event);嗯，这里模仿了系统的ScaleGestureDetector编写了MoveGestureDetector
MoveGestureDetector代码如下：
public class MoveGestureDetector
{
private Context mContext;
private PointF mPrePointer;
private PointF mCurPointer;
private boolean isGestureMoving;
private MotionEvent mPreMotionEvent;
private MotionEvent mCurrentMotionEvent;
public OnMoveGestureListener mListener;
//记录最终结果返回
private PointF mDeltaPointer = new PointF();
public MoveGestureDetector(Context context, OnMoveGestureListener listener)
{
this.mContext = context;
this.mListener = listener;
}
public float getMoveX()
{
return mDeltaPointer.x;
}
public float getMoveY()
{
return mDeltaPointer.y;
}
public boolean onTouchEvent(MotionEvent event)
{
if(!isGestureMoving)
{
handleStartEvent(event);
}else
{
handleProgressEvent(event);
}
return true;
}
private void handleProgressEvent(MotionEvent event)
{
switch (event.getAction())
{
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mListener.onMoveEnd(this);
resetState();
break;
case MotionEvent.ACTION_MOVE:
updateStateByEvent(event);
if(mListener.onMove(this))
{
mPreMotionEvent.recycle();
mPreMotionEvent = MotionEvent.obtain(event);
}
break;
}
}
private void handleStartEvent(MotionEvent event)
{
switch(event.getAction())
{
case MotionEvent.ACTION_DOWN:
resetState();
mPreMotionEvent = MotionEvent.obtain(event);
updateStateByEvent(event);
break;
case MotionEvent.ACTION_MOVE:
isGestureMoving = mListener.onMoveBegin(this);
break;
}
}
private void updateStateByEvent(MotionEvent event)
{
MotionEvent preEvent = mPreMotionEvent;
mPrePointer = calculateFocalPointer(preEvent);
mCurPointer = calculateFocalPointer(event);
boolean skipThisMoveEvent = preEvent.getPointerCount() != event.getPointerCount();
//更新deltaX和deltaY
mDeltaPointer.x = skipThisMoveEvent ? 0 : mCurPointer.x - mPrePointer.x;
mDeltaPointer.y = skipThisMoveEvent ? 0 : mCurPointer.y - mPrePointer.y;
}
private PointF calculateFocalPointer(MotionEvent event)
{
int count = event.getPointerCount();
float x = 0, y = 0;
for(int i = 0; i < count; i++)
{
x += event.getX(i);
y += event.getY(i);
}
x /= count;
y /= count;
return new PointF(x, y);
}
private void resetState()
{
if(mPreMotionEvent != null)
{
mPreMotionEvent.recycle();
mPreMotionEvent = null;
}
if(mCurrentMotionEvent != null)
{
mCurrentMotionEvent.recycle();
mCurrentMotionEvent = null;
}
isGestureMoving = false;
}
public interface OnMoveGestureListener
{
public boolean onMoveBegin(MoveGestureDetector detector);
public boolean onMove(MoveGestureDetector detector);
public void onMoveEnd(MoveGestureDetector detector);
}
public static class SimpleMoveGestureDetector implements OnMoveGestureListener
{
@Override
public boolean onMoveBegin(MoveGestureDetector detector)
{
return true;
}
@Override
public boolean onMove(MoveGestureDetector detector)
{
return false;
}
@Override
public void onMoveEnd(MoveGestureDetector detector)
{
}
}
}简单分析一下：
- OnMoveGestureListener内部接口以及SimpleMoveGestureDetector内部类都是模仿系统ScaleGestureDetector设计
- 构造方法MoveGestureDetector(Context context, OnMoveGestureListener listener)要求用户初始化OnMoveGestureListener并传递进来
- 对外公布onTouchEvent()，外部必须调用该方法，并把最新的event传递进来；
- 对外公布getMoveX()，getMoveY()，外部可以通过这两个方法，拿到Move时候最新的deltaX和deltaY
- updateStateByEvent(event)根据最新的event，更新mDeltaPointer.x和mDeltaPointer.y
- 剩余的方法：handleStartEvent(MotionEvent)；handleProgressEvent(MotionEvent)主要就是记录mPreMotionEvent，调用updateStateByEvent(MotionEvent)等来实现逻辑功能