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?.computeCurrentVelocity(1000 , mMaximumVelocity)          val velocity = velocityTracker?.xVelocity?.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    }  }

  <style name="AppTheme.Transparent" parent="Theme.AppCompat.Light.NoActionBar">    <item name="android:windowBackground">@color/transparent</item>    <item name="android:windowIsTranslucent">true</item>  </style>

<?xml version="1.0" encoding="utf-8"?><set xmlns:android="http://schemas.android.com/apk/res/android">  <translate    android:fromXDelta="100%p"    android:toXDelta="0"    android:duration="200"    android:interpolator="@android:anim/accelerate_decelerate_interpolator"/></set>

<?xml version="1.0" encoding="utf-8"?><set xmlns:android="http://schemas.android.com/apk/res/android"  android:shareInterpolator="true"  >  <translate    android:fromXDelta="0"    android:toXDelta="100%p"    android:duration="200"    android:interpolator="@android:anim/accelerate_decelerate_interpolator"/></set>

class TwoActivity : BaseActivity() {  override fun onCreate(savedInstanceState: Bundle?) {    super.onCreate(savedInstanceState)    setContentView(R.layout.activity_two)    val index = intent?.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)  }}