Android custom view achieves drawer effect

 /**
    * Since scrollBy cannot be used above, the Scroller class cannot be used here to complete smooth movement. Fortunately, we have animations
    */
  class MyAnimation extends Animation {

    private int viewCurrentLfet;
    private int viewStartLfet;
    private int viewTargetLfet;
    private int viewWidth;
    private View view;
    private int cha;

    public MyAnimation(View view, int viewStartLfet, int viewTargetLfet, int viewWidth) {
       = view;
       = viewStartLfet;
       = viewTargetLfet;
       = viewWidth;
      cha = viewTargetLfet - viewStartLfet;
      setDuration((cha));
    }

    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
      (interpolatedTime, t);

      viewCurrentLfet = (int) (viewStartLfet + cha * interpolatedTime);
      (viewCurrentLfet, 0, viewCurrentLfet + viewWidth, menuHeight);


    }
  }

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/**
 * Created by a on 2016/8/15.
 */
public class ChouTiView extends ViewGroup {

  private View mainView;
  private View menuView;
  private int menuWidth;
  private int downX;
  private int lastX;
  private int moveX;
  private int deltaX;
  private int menuLeft;
  private int mainLeft;
  private int menuHeight;
  private int mainWidth;
  private int mainHeight;
  private int menuLeftBorder;
  private int mainLeftBorder;
  private int menuRightBorder;
  private int mainRightBorder;
  private int mMaxVelocity;
  private VelocityTracker mVelocityTracker;
  private int mPointerId;
  private float velocityX;
  private float velocityY;

  public ChouTiView(Context context) {
    super(context);
    init();
  }


  public ChouTiView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
// 0. Obtain the maximum speed this time    mMaxVelocity = (getContext()).getMaximumFlingVelocity();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    (widthMeasureSpec, heightMeasureSpec);
    (widthMeasureSpec, heightMeasureSpec);
    (widthMeasureSpec, heightMeasureSpec);
// Get the correct width of the subview (only get specific numeric values), but you cannot get the height in this way, because here match-parent is -1    menuWidth = ().width;
    menuLeft = (int) (-menuWidth * 0.5);
    menuLeftBorder = (int) (-menuWidth * 0.5);
    menuRightBorder = 0;
    mainLeft = 0;
    mainLeftBorder = 0;
    mainRightBorder = menuWidth;

  }

  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    menuHeight = b;
    mainWidth = r;
    mainHeight = b;
    (l, t, r, b);
    (menuLeft, t, menuLeft + menuWidth, b);

  }

  @Override
  protected void onFinishInflate() {
    ();
    mainView = getChildAt(1);
    menuView = getChildAt(0);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    final int action = ();

    acquireVelocityTracker(event); //1. Add MotionEvent to VelocityTracker    final VelocityTracker verTracker = mVelocityTracker;
    switch (action) {

      case MotionEvent.ACTION_DOWN:
        //2. Find the id of the first contact. At this time, there may be multiple contacts, but at least one        // Get the finger id with index 0        mPointerId = (0);
        downX = (int) ();
        lastX = downX;
        break;

      case MotionEvent.ACTION_MOVE:
// Get the index corresponding to the current finger id. Although when ACTION_DOWN, we select the index as 0 by default        // The finger, but when there is a second finger touching and the previously effective finger up, we will adjust the effective finger
        // There may be multiple fingers on the screen, and we need to ensure that the movement of the same finger is used.        // Therefore, we cannot use() to obtain the index here        final int pointerIndex = (mPointerId);


        moveX = (int) (pointerIndex);
        deltaX = moveX - lastX;
// Indicate the increment caused by touch movement on the left side of menu and main        menuLeft = (int) (menuLeft + deltaX * 0.43);//Let the menu move slowly        mainLeft = mainLeft + deltaX;
// Let the menu move according to the increments of the fingers, considering the boundary problem of both sides (to achieve the movement effect by constantly laying out)// Why is scrollBy not applicable, because scrollBy moves the outer large view, now the requirement is to move two small views in this large view separately// If scrollBy, the menu and main page will be moved at the same time, and there will be no misalignment effect.// You will think, let the little view scrollBy by itself, this is not OK.// Because if a small view, for example, menu calls scrollBy, the menu's own border will move.// It seems that the text inside the menu is moving, but the menu is not moving in the big view on the outer layer.// It's difficult to say, but it really can't be used to scrollBy        if (menuLeft >= menuRightBorder) {
          menuLeft = menuRightBorder;
        } else if (menuLeft <= menuLeftBorder) {
          menuLeft = menuLeftBorder;
        }
        (menuLeft, 0, menuLeft + menuWidth, menuHeight);


// Let the main page move according to the finger increments, considering the boundary issues on both sides        if (mainLeft >= mainRightBorder) {
          mainLeft = mainRightBorder;
        } else if (mainLeft <= mainLeftBorder) {
          mainLeft = mainLeftBorder;
        }
        (mainLeft, 0, mainLeft + mainWidth, mainHeight);

        lastX = moveX;
        break;


      case MotionEvent.ACTION_UP:
        //3. Find the pseudo-instantaneous speed        (1000, mMaxVelocity);
        velocityX = (mPointerId);
        ("qwe", velocityX + "/" + mMaxVelocity);
        if (velocityX > 1000) {
          smoothToMenu();
        } else if (velocityX < -2000) {
          smoothToMain();
        } else {
// Determine the position of letting go. If the menu width is greater than 1/2.5, open the menu, otherwise open the main page
          if (mainLeft > menuWidth / 2.5) {
            ("qqq", "Show Menu");
            smoothToMenu();
          } else {
            ("qqq", "Show main page");
            smoothToMain();
          }
        }
// 4.ACTION_UP releases VelocityTracker and gives it to other controls to use        releaseVelocityTracker();
        break;
      case MotionEvent.ACTION_CANCEL:

// 4.ACTION_UP releases VelocityTracker and gives it to other controls to use        releaseVelocityTracker();

      case MotionEvent.ACTION_POINTER_UP:
        // Get the index of the fingers leaving the screen        int pointerIndexLeave = ();
        int pointerIdLeave = (pointerIndexLeave);
        if (mPointerId == pointerIdLeave) {
          // The current valid fingers that leave the screen need to be readjusted here and VelocityTracker needs to be reset          int reIndex = pointerIndexLeave == 0 ? 1 : 0;
          mPointerId = (reIndex);
          // Adjust the touch position to prevent jumps          downX = (int) (reIndex);
//          y = (reIndex);
          releaseVelocityTracker();
        }
        releaseVelocityTracker();

        break;
    }


    return true;
  }

  private void smoothToMain() {
    MyAnimation menuAnimation = new MyAnimation(menuView, menuLeft, menuLeftBorder, menuWidth);
    MyAnimation mainAnimation = new MyAnimation(mainView, mainLeft, mainLeftBorder, mainWidth);
    AnimationSet animationSet = new AnimationSet(true);
    (menuAnimation);
    (mainAnimation);
    startAnimation(animationSet);
    //Remember to update the left state of menu and main, which affects the animation when touching the finger again, otherwise it will change suddenly    menuLeft = menuLeftBorder;
    mainLeft = mainLeftBorder;
  }

  private void smoothToMenu() {
    MyAnimation menuAnimation = new MyAnimation(menuView, menuLeft, menuRightBorder, menuWidth);
    MyAnimation mainAnimation = new MyAnimation(mainView, mainLeft, mainRightBorder, mainWidth);
    AnimationSet animationSet = new AnimationSet(true);
    (menuAnimation);
    (mainAnimation);
    startAnimation(animationSet);
    //Remember to update the left state of menu and main, which affects the animation when touching the finger again, otherwise it will change suddenly    menuLeft = menuRightBorder;
    mainLeft = mainRightBorder;
  }


  /**
    * @param event Add MotionEvent to VelocityTracker
    * @see #obtain()
    * @see #addMovement(MotionEvent)
    */
  private void acquireVelocityTracker(final MotionEvent event) {
    if (null == mVelocityTracker) {
      mVelocityTracker = ();
    }
    (event);
  }

  /**
    * Release VelocityTracker
    *
    * @see #clear()
    * @see #recycle()
    */
  private void releaseVelocityTracker() {
    if (null != mVelocityTracker) {
      ();
      ();
      mVelocityTracker = null;
    }
  }


  /**
    * Since scrollBy cannot be used above, the Scroller class cannot be used here to complete smooth movement. Fortunately, we have animations
    */
  class MyAnimation extends Animation {

    private int viewCurrentLfet;
    private int viewStartLfet;
    private int viewTargetLfet;
    private int viewWidth;
    private View view;
    private int cha;

    public MyAnimation(View view, int viewStartLfet, int viewTargetLfet, int viewWidth) {
       = view;
       = viewStartLfet;
       = viewTargetLfet;
       = viewWidth;
      cha = viewTargetLfet - viewStartLfet;
      setDuration((cha));
    }

    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
      (interpolatedTime, t);

      viewCurrentLfet = (int) (viewStartLfet + cha * interpolatedTime);
      (viewCurrentLfet, 0, viewCurrentLfet + viewWidth, menuHeight);


    }
  }

}