怎么在Android中通過(guò)自定義View實(shí)現(xiàn)一個(gè)抽屜效果

 /**
   * 由于上面不能使用scrollBy，那么這里就不能使用Scroller這個(gè)類來(lái)完成平滑移動(dòng)了，還好我們有動(dòng)畫(huà)
   */
  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.獲得此次最大速率
    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);
//    獲得子View的正確寬度（只能獲取具體的數(shù)字值）,但是不能這樣獲取高度，因?yàn)檫@里match—parent為-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.求第一個(gè)觸點(diǎn)的id， 此時(shí)可能有多個(gè)觸點(diǎn)，但至少一個(gè)
        // 獲取索引為0的手指id
        mPointerId = event.getPointerId(0);
        downX = (int) event.getX();
        lastX = downX;
        break;

      case MotionEvent.ACTION_MOVE:
// 獲取當(dāng)前手指id所對(duì)應(yīng)的索引，雖然在ACTION_DOWN的時(shí)候，我們默認(rèn)選取索引為0
        // 的手指，但當(dāng)有第二個(gè)手指觸摸，并且先前有效的手指up之后，我們會(huì)調(diào)整有效手指

        // 屏幕上可能有多個(gè)手指，我們需要保證使用的是同一個(gè)手指的移動(dòng)軌跡，
        // 因此此處不能使用event.getActionIndex()來(lái)獲得索引
        final int pointerIndex = event.findPointerIndex(mPointerId);


        moveX = (int) event.getX(pointerIndex);
        deltaX = moveX - lastX;
//        把觸摸移動(dòng)引起的增量，體現(xiàn)在menu和main的左側(cè)left上
        menuLeft = (int) (menuLeft + deltaX * 0.43);//讓菜單移動(dòng)的慢一點(diǎn)
        mainLeft = mainLeft + deltaX;
//        讓菜單根據(jù)手指增量移動(dòng)，考慮兩側(cè)邊界問(wèn)題（通過(guò)不停地layout實(shí)現(xiàn)移動(dòng)效果）
//        為何不適用scrollBy，因?yàn)閟crollBy移動(dòng)的是外層的大View，現(xiàn)在需求是分別移動(dòng)這個(gè)大view內(nèi)的兩個(gè)小View
//        scrollBy的話，會(huì)讓菜單和主頁(yè)面同時(shí)移動(dòng)，不會(huì)產(chǎn)生錯(cuò)位效果，
//        你會(huì)想，那讓小view自己scrollBy，這樣也是不行的，
//        因?yàn)樽屝iew，例如menu調(diào)用scrollBy的話，會(huì)讓menu自己的邊框在動(dòng)，
//        看上去，是menu內(nèi)部的文字在移動(dòng)，但是menu并沒(méi)有在外層的大View里移動(dòng)
//        說(shuō)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);


//        讓主頁(yè)面根據(jù)手指增量移動(dòng)，考慮兩側(cè)邊界問(wèn)題
        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.求偽瞬時(shí)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 {
//        判斷松手的位置，如果大于1/2.5的菜單寬度就打開(kāi)菜單，否則打開(kāi)主頁(yè)面

          if (mainLeft > menuWidth / 2.5) {
            Log.e("qqq", "顯示菜單");
            smoothToMenu();
          } else {
            Log.e("qqq", "顯示主頁(yè)面");
            smoothToMain();
          }
        }
//        4.ACTION_UP釋放VelocityTracker,交給其他控件使用
        releaseVelocityTracker();
        break;
      case MotionEvent.ACTION_CANCEL:

//        4.ACTION_UP釋放VelocityTracker,交給其他控件使用
        releaseVelocityTracker();

      case MotionEvent.ACTION_POINTER_UP:
        // 獲取離開(kāi)屏幕的手指的索引
        int pointerIndexLeave = event.getActionIndex();
        int pointerIdLeave = event.getPointerId(pointerIndexLeave);
        if (mPointerId == pointerIdLeave) {
          // 離開(kāi)屏幕的正是目前的有效手指，此處需要重新調(diào)整，并且需要重置VelocityTracker
          int reIndex = pointerIndexLeave == 0 &#63; 1 : 0;
          mPointerId = event.getPointerId(reIndex);
          // 調(diào)整觸摸位置，防止出現(xiàn)跳動(dòng)
          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);
    //一定記得更新menu和main的左側(cè)狀態(tài)，這影響到了，再次手指觸摸時(shí)候的動(dòng)畫(huà)，否則突變
    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);
    //一定記得更新menu和main的左側(cè)狀態(tài)，這影響到了，再次手指觸摸時(shí)候的動(dòng)畫(huà)，否則突變
    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);
  }

  /**
   * 釋放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，那么這里就不能使用Scroller這個(gè)類來(lái)完成平滑移動(dòng)了，還好我們有動(dòng)畫(huà)
   */
  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);


    }
  }

}