怎么在Android中通过自定义View实现一个抽屉效果

 /**
   * 由于上面不能使用scrollBy，那么这里就不能使用Scroller这个类来完成平滑移动了，还好我们有动画
   */
  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) {
      this.view = view;
      this.viewStartLfet = viewStartLfet;
      this.viewTargetLfet = viewTargetLfet;
      this.viewWidth = viewWidth;
      cha = viewTargetLfet - viewStartLfet;
      setDuration(Math.abs(cha));
    }

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

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


    }
  }

package com.sunshine.choutidemo;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.AnimationSet;
import android.view.animation.Transformation;

/**
 * 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.获得此次最大速率
    mMaxVelocity = ViewConfiguration.get(getContext()).getMaximumFlingVelocity();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    mainView.measure(widthMeasureSpec, heightMeasureSpec);
    menuView.measure(widthMeasureSpec, heightMeasureSpec);
//    获得子View的正确宽度（只能获取具体的数字值）,但是不能这样获取高度，因为这里match—parent为-1
    menuWidth = menuView.getLayoutParams().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;
    mainView.layout(l, t, r, b);
    menuView.layout(menuLeft, t, menuLeft + menuWidth, b);

  }

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

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

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

      case MotionEvent.ACTION_DOWN:
        //2.求第一个触点的id， 此时可能有多个触点，但至少一个
        // 获取索引为0的手指id
        mPointerId = event.getPointerId(0);
        downX = (int) event.getX();
        lastX = downX;
        break;

      case MotionEvent.ACTION_MOVE:
// 获取当前手指id所对应的索引，虽然在ACTION_DOWN的时候，我们默认选取索引为0
        // 的手指，但当有第二个手指触摸，并且先前有效的手指up之后，我们会调整有效手指

        // 屏幕上可能有多个手指，我们需要保证使用的是同一个手指的移动轨迹，
        // 因此此处不能使用event.getActionIndex()来获得索引
        final int pointerIndex = event.findPointerIndex(mPointerId);


        moveX = (int) event.getX(pointerIndex);
        deltaX = moveX - lastX;
//        把触摸移动引起的增量，体现在menu和main的左侧left上
        menuLeft = (int) (menuLeft + deltaX * 0.43);//让菜单移动的慢一点
        mainLeft = mainLeft + deltaX;
//        让菜单根据手指增量移动，考虑两侧边界问题（通过不停地layout实现移动效果）
//        为何不适用scrollBy，因为scrollBy移动的是外层的大View，现在需求是分别移动这个大view内的两个小View
//        scrollBy的话，会让菜单和主页面同时移动，不会产生错位效果，
//        你会想，那让小view自己scrollBy，这样也是不行的，
//        因为让小view，例如menu调用scrollBy的话，会让menu自己的边框在动，
//        看上去，是menu内部的文字在移动，但是menu并没有在外层的大View里移动
//        说的很拗口，但是真的不能用scrollBy
        if (menuLeft >= menuRightBorder) {
          menuLeft = menuRightBorder;
        } else if (menuLeft <= menuLeftBorder) {
          menuLeft = menuLeftBorder;
        }
        menuView.layout(menuLeft, 0, menuLeft + menuWidth, menuHeight);


//        让主页面根据手指增量移动，考虑两侧边界问题
        if (mainLeft >= mainRightBorder) {
          mainLeft = mainRightBorder;
        } else if (mainLeft <= mainLeftBorder) {
          mainLeft = mainLeftBorder;
        }
        mainView.layout(mainLeft, 0, mainLeft + mainWidth, mainHeight);

        lastX = moveX;
        break;


      case MotionEvent.ACTION_UP:
        //3.求伪瞬时速度
        verTracker.computeCurrentVelocity(1000, mMaxVelocity);
        velocityX = verTracker.getXVelocity(mPointerId);
        Log.e("qwe", velocityX + "/" + mMaxVelocity);
        if (velocityX > 1000) {
          smoothToMenu();
        } else if (velocityX < -2000) {
          smoothToMain();
        } else {
//        判断松手的位置，如果大于1/2.5的菜单宽度就打开菜单，否则打开主页面

          if (mainLeft > menuWidth / 2.5) {
            Log.e("qqq", "显示菜单");
            smoothToMenu();
          } else {
            Log.e("qqq", "显示主页面");
            smoothToMain();
          }
        }
//        4.ACTION_UP释放VelocityTracker,交给其他控件使用
        releaseVelocityTracker();
        break;
      case MotionEvent.ACTION_CANCEL:

//        4.ACTION_UP释放VelocityTracker,交给其他控件使用
        releaseVelocityTracker();

      case MotionEvent.ACTION_POINTER_UP:
        // 获取离开屏幕的手指的索引
        int pointerIndexLeave = event.getActionIndex();
        int pointerIdLeave = event.getPointerId(pointerIndexLeave);
        if (mPointerId == pointerIdLeave) {
          // 离开屏幕的正是目前的有效手指，此处需要重新调整，并且需要重置VelocityTracker
          int reIndex = pointerIndexLeave == 0 ? 1 : 0;
          mPointerId = event.getPointerId(reIndex);
          // 调整触摸位置，防止出现跳动
          downX = (int) event.getX(reIndex);
//          y = event.getY(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);
    animationSet.addAnimation(menuAnimation);
    animationSet.addAnimation(mainAnimation);
    startAnimation(animationSet);
    //一定记得更新menu和main的左侧状态，这影响到了，再次手指触摸时候的动画，否则突变
    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);
    animationSet.addAnimation(menuAnimation);
    animationSet.addAnimation(mainAnimation);
    startAnimation(animationSet);
    //一定记得更新menu和main的左侧状态，这影响到了，再次手指触摸时候的动画，否则突变
    menuLeft = menuRightBorder;
    mainLeft = mainRightBorder;
  }


  /**
   * @param event 向VelocityTracker添加MotionEvent
   * @see android.view.VelocityTracker#obtain()
   * @see android.view.VelocityTracker#addMovement(MotionEvent)
   */
  private void acquireVelocityTracker(final MotionEvent event) {
    if (null == mVelocityTracker) {
      mVelocityTracker = VelocityTracker.obtain();
    }
    mVelocityTracker.addMovement(event);
  }

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


  /**
   * 由于上面不能使用scrollBy，那么这里就不能使用Scroller这个类来完成平滑移动了，还好我们有动画
   */
  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) {
      this.view = view;
      this.viewStartLfet = viewStartLfet;
      this.viewTargetLfet = viewTargetLfet;
      this.viewWidth = viewWidth;
      cha = viewTargetLfet - viewStartLfet;
      setDuration(Math.abs(cha));
    }

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

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


    }
  }

}