Android使用BitmapRegionDecoder获取指定区域的图片

Android系统处理图片方面并不怎么理想，稍不注意就会内存溢出。在处理大尺寸图片时，有时候只需要显示指定区域的图片，Android在2.3中提供了BitmapRegionDecoder类来解决此问题。

关于解决Bitmap加载内存溢出问题，可以查看Android使用BitmapFactory.Options解决加载大图片内存溢出问题。

public class DisplayImageRegionActivity extends Activity implements OnTouchListener {
private final Rect mRect = new Rect();
private BitmapRegionDecoder mDecoder;
private ImageView mView;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

mView = new ImageView(this);
mView.setAdjustViewBounds(true);
mView.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
mView.setScaleType(ScaleType.CENTER);
mView.setOnTouchListener(this);
setContentView(mView);

try {
InputStream is = getResources().openRawResource(R.drawable.a);
mDecoder = BitmapRegionDecoder.newInstance(is, true);
} catch (IOException e) {
e.printStackTrace();
}
}

@Override
public boolean onTouch(View v, MotionEvent event) {
final int action = event.getAction() & MotionEvent.ACTION_MASK;
final int x = (int) event.getX();
final int y = (int) event.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
setImageRegion(x, y);
break;
}
return true;
}

private void setImageRegion(int left, int top) {
//        BitmapFactory.Options opts = new BitmapFactory.Options();
final int width = mView.getWidth();
final int height = mView.getHeight();

final int imgWidth = mDecoder.getWidth();
final int imgHeight = mDecoder.getHeight();

int right = left + width;
int bottom = top + height;
if(right > imgWidth) right = imgWidth;
if(bottom > imgHeight) bottom = imgHeight;
if(left < 0) left = 0;
if(top < 0) top = 0;

mRect.set(left, top, right, bottom);
Bitmap bm = mDecoder.decodeRegion(mRect, null);
mView.setImageBitmap(bm);
}
}

转自：http://orgcent.com/android-bitmapregiondecoder-image/