Android custom control ScrollView implements up and down swipe function

package ;

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public class MyScrollView extends ViewGroup {

  private int mScreeHeight;//Screen height  private Scroller mScroller;
  private int mLastY;
  private int mStart;
  private int mEnd;
  private Context context;


  public MyScrollView(Context context) {
    super(context);
    initView(context);
  }

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

  public MyScrollView(Context context, AttributeSet attrs,
            int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initView(context);
  }


  private void initView(Context context) {
    WindowManager wm = (WindowManager) (Context.WINDOW_SERVICE);
    //The DisplayMetrics class provides common information about displays, such as display size, resolution, and fonts.    DisplayMetrics dm = new DisplayMetrics();
    ().getMetrics(dm);
    mScreeHeight = ;//Height (pixel)    mScroller = new Scroller(context);
  }

  //Inheriting the method that must be implemented in ViewGroup  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    int childCount = getChildCount();//Get the number of subviews    //Set the height of the ViewGroup    MarginLayoutParams mlp = (MarginLayoutParams) getLayoutParams();
     = mScreeHeight * childCount;
    setLayoutParams(mlp);
    for (int i = 0; i < childCount; i++) {
      View child = getChildAt(i);
      if (() != ) {
        //The parameter is relative to the upper left and lower right position relative to the parent container, the third parameter must be r        (0, i * mScreeHeight, r, (i + 1) * mScreeHeight);
      }
    }
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    (widthMeasureSpec, heightMeasureSpec);
    int count = getChildCount();
    for (int i = 0; i < count; i++) {
      View child = getChildAt(i);
      measureChild(child, widthMeasureSpec, heightMeasureSpec);
    }
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    int y = (int) ();//Relative to the y value of view, getRawY() is relative to the screen    switch (()) {
      case MotionEvent.ACTION_DOWN:
        mLastY = y;//The last y value        mStart = getScrollY();//Record the touch starting point        break;
      case MotionEvent.ACTION_MOVE:
        if(!()) {
          ();//Give up moving to the final position        }
        int dy = mLastY - y;//Offset distance        //If the sliding distance is less than 0 or greater than the screen height, no offset        if(getScrollY()<0){
          dy = 0;
        }
        if(getScrollY() > getHeight()-mScreeHeight){
          dy = 0;
        }
        scrollBy(0,dy);//move        mLastY = y;
        break;
      case MotionEvent.ACTION_UP:
        int dScrollY = checkAlignment();//The distance of overall movement        if(dScrollY > 0){
          if(dScrollY < mScreeHeight / 3){
            (0,getScrollY(),0,-dScrollY);
          }else{
            (0,getScrollY(),0,mScreeHeight-dScrollY);
          }
        }else{
          if(-dScrollY < mScreeHeight / 3){
            (0,getScrollY(),0,-dScrollY);
          }else{
            (0,getScrollY(),0,-mScreeHeight-dScrollY);
          }
        }
        break;
    }
    postInvalidate();
    return true;
  }

  private int checkAlignment(){
     mEnd = getScrollY();//Record touch end point    boolean isUp = ((mEnd - mStart)>0) ? true : false;
    int lastPrev = mEnd % mScreeHeight;
    int lastNext = mScreeHeight - lastPrev;
    if(isUp){
      return lastPrev;//up    }else
      return -lastNext;
  }

  @Override
  public void computeScroll() {
    ();
    if(()){//Return true, indicating that the move has not been completed yet      scrollTo(0,());//Move to current location      postInvalidate();
      //invalidate() is used to refresh the View and must be done in the UI thread.      //postInvalidate() can be called in non-UI thread    }
  }
}

DisplayMetrics metric = new DisplayMetrics(); 
// Used after API 17, the acquired pixel width and height contain the space occupied by virtual keys, and is obtained by reflection before API 17().getDefaultDisplay().getRealMetrics(metric); 
//The pixel width and height obtained do not contain the space occupied by the virtual key//().getDefaultDisplay().getMetrics(metric); 
int width = ; // Width (pixels)int height = ; // Height (pixel)float density = ; // dp scaling factorint densityDpi = ; // Generalized densityfloat xdpi = ;//The true density of the x-axis directionfloat ydpi = ;//The true density of the y-axis direction

private int getStatusBarHeight() { 
  Rect rect = new Rect(); 
  getWindow().getDecorView().getWindowVisibleDisplayFrame(rect); 
  return ; 
}