大图不撑爆内存

答案 ：分片显示

使用系统提供的BitmapRegionDecoder类可以完成。

BitmapRegionDecoder：区域解码器
可以解码一个矩形区域的图像，
可以自定义一块矩形的区域，
根据手势来移动矩形区域的位置就能看到整张图片了。

//初始化变量
private void init(){

//用来配置Bitmap相关的参数
//如获取Bitmap的宽高 内存复用等参数。
    mOptions = new BitmapFactory.Options();
    //滑动器
    mScroller = new Scroller(getContext());
    //所放器
    mMatrix = new Matrix();
    //手势识别 双击事件
    mGestureDetector = new GestureDetector(getContext(),this);

   //手势识别 缩放事件
    mScaleGestureDetector = new ScaleGestureDetector(getContext(),this);
}



//设置需要加载的图片
// 通过BitmapFactory.Options拿到图片的真实宽高
public void setImage(InputStream is){
    mOptions.inJustDecodeBounds = true;
    BitmapFactory.decodeStream(is,null,mOptions);
    mImageWidth = mOptions.outWidth;
    mImageHeight = mOptions.outHeight;

   //去掉透明通道
    mOptions.inPreferredConfig = Bitmap.Config.RGB_565;
    mOptions.inJustDecodeBounds = false;
    try {
        //区域解码器
        mRegionDecoder = BitmapRegionDecoder.newInstance(is,false);
    } catch (IOException e) {
        e.printStackTrace();
    }
    requestLayout();
}


//获取View的宽高，计算缩放值
// 视图的大小发生更改时被调用
// 第一次在onMeasure之后被调用，可拿到View的宽高。
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    mViewWidth = w;
    mViewHeight = h;
    mRect.top = 0;
    mRect.left = 0;
    mRect.right = (int) mViewWidth;
    mRect.bottom = (int) mViewHeight;
    mScale = mViewWidth/mImageWidth;
    mCurrentScale = mScale;
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if(mRegionDecoder == null){
        return;
    }
    //复用内存
    mOptions.inBitmap = mBitmap;
    mBitmap = mRegionDecoder.decodeRegion(mRect,mOptions);
    mMatrix.setScale(mCurrentScale,mCurrentScale);
    canvas.drawBitmap(mBitmap,mMatrix,null);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    mGestureDetector.onTouchEvent(event);

    mScaleGestureDetector.onTouchEvent(event);
    return true;
}

@Override
public boolean onDown(MotionEvent e) {
    //如果正在滑动，先停止
    if(!mScroller.isFinished()){
        mScroller.forceFinished(true);
    }
    return true;
}


@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
    //滑动的时候，改变mRect显示区域的位置
    mRect.offset((int)distanceX,(int)distanceY);
    //处理上下左右的边界
    if(mRect.left<0){
        mRect.left = 0;
        mRect.right = (int) (mViewWidth/mCurrentScale);
    }
    if(mRect.right>mImageWidth){
        mRect.right = (int) mImageWidth;
        mRect.left = (int) (mImageWidth-mViewWidth/mCurrentScale);
    }
    if(mRect.top<0){
        mRect.top = 0;
        mRect.bottom = (int) (mViewHeight/mCurrentScale);
    }
    if(mRect.bottom>mImageHeight){
        mRect.bottom = (int) mImageHeight;
        mRect.top = (int) (mImageHeight-mViewHeight/mCurrentScale);
    }
    invalidate();
    return false;
}


@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    mScroller.fling(mRect.left,mRect.top,-(int)velocityX,-(int)velocityY,0,(int)mImageWidth
            ,0,(int)mImageHeight);
    return false;
}

@Override
public void computeScroll() {
    super.computeScroll();
    if(!mScroller.isFinished()&&mScroller.computeScrollOffset()){
        if(mRect.top+mViewHeight/mCurrentScale<mImageHeight){
            mRect.top = mScroller.getCurrY();
            mRect.bottom = (int) (mRect.top + mViewHeight/mCurrentScale);
        }
        if(mRect.bottom>mImageHeight) {
            mRect.top = (int) (mImageHeight - mViewHeight/mCurrentScale);
            mRect.bottom = (int) mImageHeight;
        }
        invalidate();
    }
}



@Override
public boolean onDoubleTap(MotionEvent e) {
    //处理双击事件
    if (mCurrentScale>mScale){
        mCurrentScale = mScale;
    } else {
        mCurrentScale = mScale*mMultiple;
    }
    mRect.right = mRect.left+(int)(mViewWidth/mCurrentScale);
    mRect.bottom = mRect.top+(int)(mViewHeight/mCurrentScale);
    //处理边界
    if(mRect.left<0){
        mRect.left = 0;
        mRect.right = (int) (mViewWidth/mCurrentScale);
    }
    if(mRect.right>mImageWidth){
        mRect.right = (int) mImageWidth;
        mRect.left = (int) (mImageWidth-mViewWidth/mCurrentScale);
    }
    if(mRect.top<0){
        mRect.top = 0;
        mRect.bottom = (int) (mViewHeight/mCurrentScale);
    }
    if(mRect.bottom>mImageHeight){
        mRect.bottom = (int) mImageHeight;
        mRect.top = (int) (mImageHeight-mViewHeight/mCurrentScale);
    }
    
    invalidate();
    return true;
}


@Override
public boolean onScale(ScaleGestureDetector detector) {
    //处理手指缩放事件
    //获取与上次事件相比，得到的比例因子
    float scaleFactor = detector.getScaleFactor();
//        mCurrentScale+=scaleFactor-1;
    mCurrentScale*=scaleFactor;
    if(mCurrentScale>mScale*mMultiple){
        mCurrentScale = mScale*mMultiple;
    }else if(mCurrentScale<=mScale){
        mCurrentScale = mScale;
    }
    mRect.right = mRect.left+(int)(mViewWidth/mCurrentScale);
    mRect.bottom = mRect.top+(int)(mViewHeight/mCurrentScale);
    invalidate();
    return true;
}

@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
    //当 >= 2 个手指碰触屏幕时调用
   //若返回 false 则忽略改事件调用
    return true;
}

摘取自网络 ，已备自己学习。
https://www.jianshu.com/p/dacdfcf95596