安卓，自定义滑动菜单，设置背景后，滑动起来很卡

public class MainUI extends FrameLayout{

private Context context;

private LinearLayout layout;
private LinearLayout backLayout;
private LinearLayout leftMenu;
private LinearLayout rightMenu;

private Scroller mScroller;
private int mScreenWidth;
public MainUI(Context context) {
    super(context);
    initView(context);
}

public MainUI(Context context, AttributeSet attrs) {
    super(context, attrs);
    initView(context);
}

private void initView(Context context){
    this.context=context;
    this.mScroller=new Scroller(context,new DecelerateInterpolator());
    layout=new LinearLayout(context);
    layout.setBackgroundColor(Color.BLUE);
    leftMenu=new LinearLayout(context);

// leftMenu= (LinearLayout) LayoutInflater.from(context).inflate(R.layout.left_menu_item,null);
leftMenu.setBackgroundColor(Color.YELLOW);
rightMenu=new LinearLayout(context);
rightMenu.setBackgroundColor(Color.GREEN);
backLayout=new LinearLayout(context);
backLayout.setBackgroundColor(0x88000000);
addView(leftMenu);
addView(layout);
addView(rightMenu);
addView(backLayout);
layout.setScaleX(1);
layout.setScaleY(1);
backLayout. setAlpha(0);
backLayout.setScaleX(1);
backLayout.setScaleY(1);

    WindowManager manager= (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    DisplayMetrics metrics=new DisplayMetrics();
    manager.getDefaultDisplay().getMetrics(metrics);
    mScreenWidth=metrics.widthPixels;
}


@Override
public void scrollTo(int x, int y) {
    super.scrollTo(x, y);
    float curX=  Math.abs(getScrollX());
    float scale=curX /leftMenu.getMeasuredWidth();
    backLayout.setAlpha(scale);

    float xxx=(float)(leftMenu.getMeasuredWidth()-Math.sqrt(Math.abs(x)*2))/leftMenu.getMeasuredWidth();
    layout.setScaleX(xxx);
    layout.setScaleY(xxx);
    backLayout.setScaleX(xxx);
    backLayout.setScaleY(xxx);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    this.layout.measure(widthMeasureSpec, heightMeasureSpec);
    this.backLayout.measure(widthMeasureSpec, heightMeasureSpec);
    /**实际宽度*/
    int realWidth=MeasureSpec.getSize(widthMeasureSpec);
    //AT_MOST 自适应，EXACTLY精准
    int menuWidth=MeasureSpec.makeMeasureSpec((int)(realWidth * 0.8f),MeasureSpec.EXACTLY);
    leftMenu.measure(menuWidth, heightMeasureSpec);
    rightMenu.measure(menuWidth, heightMeasureSpec);
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);
    layout.layout(left, top, right, bottom);
    backLayout.layout(left, top, right, bottom);
    leftMenu.layout(left - leftMenu.getMeasuredWidth(), top, right, bottom);
    rightMenu.layout(left + layout.getMeasuredWidth(),top,left + layout.getMeasuredWidth()+ rightMenu.getMeasuredWidth(),bottom);
}

/**判断是什么事件*/
private boolean isTestCompete;
private boolean isLeftRight;

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    if(!isTestCompete){
        getEventType(ev);
        return true;
    }
    if(isLeftRight){
        switch (ev.getAction()){
            case MotionEvent.ACTION_MOVE:
                int curScrollX=getScrollX();
                int dis_x= (int) (ev.getX()-point.x);
                int expectX=-dis_x + curScrollX;
                int finalX;
                if(expectX<0){//向左
                    finalX=Math.max(expectX,-leftMenu.getMeasuredWidth());
                }else{//向右
                    finalX=Math.min(expectX, rightMenu.getMeasuredWidth());
                }
                scrollTo(finalX,0);
                point.x= (int) ev.getX();
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                int mScraleX=getScrollX();
                if(Math.abs(mScraleX) > leftMenu.getMeasuredWidth()/ 3){
                    if(mScraleX<0){
                        mScroller.startScroll(mScraleX,0, -leftMenu.getMeasuredWidth()-mScraleX,0);
                    }else{
                        mScroller.startScroll(mScraleX,0,leftMenu.getMeasuredWidth()-mScraleX,0);
                    }
                }else{
                    mScroller.startScroll(mScraleX,0, -mScraleX,0);
                }
                invalidate();
                isLeftRight=false;
                isTestCompete=false;
                break;
            default:
                break;
        }
    }else{
        switch (ev.getAction()){
            case  MotionEvent.ACTION_UP:
                isLeftRight=false;
                isTestCompete=false;
                break;
            default:
                    break;
        }

    }
    return super.dispatchTouchEvent(ev);
}

@Override
public void computeScroll() {
    super.computeScroll();
    if(!mScroller.computeScrollOffset()){
        return;
    }
    scrollTo(mScroller.getCurrX(),0);
}

private Point point=new Point();
private static final int TEST_DIS=20;
private void getEventType(MotionEvent ev) {
    switch (ev.getAction()){
        case MotionEvent.ACTION_DOWN:
            point.x= (int) ev.getX();
            point.y= (int) ev.getY();

            break;
        case MotionEvent.ACTION_MOVE:
            int dX= (int) Math.abs(ev.getX()-point.x);
            int dY= (int) Math.abs(ev.getY()-point.y);
            if(dX >=TEST_DIS && dX>dY){//左右滑动
                isLeftRight=true;
                isTestCompete=true;
                point.x= (int) ev.getX();
                point.y= (int) ev.getY();
            }else if(dY>TEST_DIS && dY>dX){//上下滑动
                isLeftRight=false;
                isTestCompete=true;
                point.x= (int) ev.getX();
                point.y= (int) ev.getY();
            }
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:

            break;
    }
}

}

在 initView 方法中 leftMenu= (LinearLayout) LayoutInflater.from(context).inflate(R.layout.left_menu_item,null);
这个View里面，就只有一个LinearLayout,单单设置了一个背景图片

你在scrollTo()方法中调用layout的setScaleX()，这应该会导致变卡。