Android左滑返回功能的实现示例代码

  override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
    val action = ev.action
    when (action){
      MotionEvent.ACTION_DOWN -> {
        mLastX = ev.x.toInt()
        mIsDrag = false
      }
      MotionEvent.ACTION_MOVE -> {
        mScroller.computeScrollOffset()
        mIsDrag = !mScroller.isFinished

        val deltaY:Int = ev.x.toInt() - mLastX
        if (deltaY >= mTouchSlop){
          mIsDrag = true
        }
      }
    }
    return mIsDrag
  }

  override fun onTouchEvent(event: MotionEvent): Boolean {

    val action = event.action
    //1.初始化轨迹
    initVelocityTrackerIfNotExists(event)

    when(action){
      MotionEvent.ACTION_DOWN -> {
        //2.down 事件 mScroller放弃动画 记录触摸的位置
        if (!mScroller.isFinished){
          mScroller.abortAnimation()
        }

        mLastX = event.rawX.toInt()
        mIsDrag = true
        dispatchScroll(0 , 0 , slideState)
      }
      MotionEvent.ACTION_MOVE -> {
        //3.move事件调用performDrag()方法 会调用offsetLeftAndRight() 从而移动View
        val currentX = event.rawX.toInt()
        val deltaX = currentX - mLastX
        log("x = ${event.rawX} y = ${event.rawX}")
        performDrag(deltaX)
        log("deltaX = $deltaX")
        mLastX = currentX
      }
      MotionEvent.ACTION_UP,
      MotionEvent.ACTION_CANCEL ->{
        //4.up事件 主要处理手指离开后的View的滚动,以及是否要达到销毁的条件
        //endDrag()方法会处理手指离开后的动画以及是否达到销毁条件
        if (mIsDrag){
          mLastX = 0
          mIsDrag = false
          velocityTracker&＃63;.computeCurrentVelocity(1000 , mMaximumVelocity)
          val velocity = velocityTracker&＃63;.xVelocity&＃63;.toInt()!!

          isReachFinish = endDrag(velocity)
          postInvalidateOnAnimation()

          recycleVelocityTracker()
        }
      }
    }
    return true
  }

  //开始拖动
  private fun performDrag(x:Int){
    var canOffset = false
    isDragLeft = x > 0
    slideState = SlideState.DRAGGING
    //计算 滚动的 距离
    if (slideModel == DirectionModel.ONLY_LEFT ){
      if (x > 0){
        offsetLeftAndRight(x)
        canOffset = true
      }
    }else if (slideModel == DirectionModel.ONLY_RIGHT){
      if (x<0){
        offsetLeftAndRight(x)
        canOffset = true
      }
    }else{
      offsetLeftAndRight(x)
      canOffset = true
    }

    if (canOffset){
      dispatchScroll(x , left , slideState)
    }
  }

  //手指离开后的动作
  fun endDrag(xVelocity:Int):Boolean{

    slideState = SlideState.SETTLING
    val left = this.left
    log( "left = $left screenWidth * FACTOR= ${screenWidth * FACTOR}")
    log( "xVelocity = $xVelocity mMinimumVelocity= $mMinimumVelocity")
    if (Math.abs(left) > screenWidth * FACTOR
        || xVelocity > mMinimumVelocity){
      if (left>0){
        //左滑动
        mScroller.startScroll(left , 0 , screenWidth - left , 0)
      }else{
        //右滑动
        mScroller.startScroll(left , 0 , left - screenWidth , 0)
      }
      return true
    }else{
      mScroller.startScroll(left , 0 , -left , 0)
      return false
    }
  }

<&＃63;xml version="1.0" encoding="utf-8"&＃63;>


  

<&＃63;xml version="1.0" encoding="utf-8"&＃63;>


  

class TwoActivity : BaseActivity() {

  override fun onCreate(savedInstanceState: Bundle&＃63;) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_two)

    val index = intent&＃63;.getStringExtra("index")

    nextBtn.setOnClickListener {
      startActivity(Intent(this@TwoActivity , TwoActivity::class.java))
      overridePendingTransition(R.anim.enter, 0)
    }

    //滑动达到finish的监听事件，slideFinishLayout没有做任何处理 如果这里不掉用finish也不会退出activity
    slideFinishLayout.finishListener = {
      finish()
      overridePendingTransition(0, 0)
    }
  }

  override fun finish() {
    super.finish()
    overridePendingTransition(0, R.anim.exit)
  }
}