前言

突然发现微信下拉小程序入口动画非常细腻，比较好奇，所以仿照他做了一个，并不是很完美，部分效果还没完成，但总体自我感觉还不错，效果如下：

微信原版

仿照效果

流程分析

自定义ViewGroup

整个布局是通过自定义ViewGroup来管理的，在自定义ViewGroup中，子布局一共有两个，一个是小程序布局，一个是会话列表布局，然后按照上下分别摆放就可以了。

package com.example.kotlindemo.widget.weixin

import android.content.Context
import android.content.res.Resources
import android.util.AttributeSet
import android.util.Log
import android.view.MotionEvent
import android.view.View
import android.view.ViewGroup
import androidx.core.view.ViewCompat
import androidx.customview.widget.ViewDragHelper
import com.example.kotlindemo.R
import java.math.BigDecimal

class WeiXinMainPullViewGroup @JvmOverloads constructor(
    context: Context?,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : ViewGroup(context, attrs, defStyleAttr) {

    public var viewDragHelper: ViewDragHelper = ViewDragHelper.create(this, 0.5f, DragHandler());

    var headerMaskView: WeiXinPullHeaderMaskView? = null

    var isOpen: Boolean = false;

    val NAVIGAATION_HEIGHT = 100

    init {

    }

    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {

        for (index in 0 until childCount) {
            if (getChildAt(index) != headerMaskView) {
                getChildAt(index).layout(l, paddingTop, r, b)
            }
        }

    }

    override fun computeScroll() {
        if (viewDragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }

    }

    override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
        Log.i("TAG", "onInterceptTouchEvent: ${ev.action}")
        MotionEvent.ACTION_MOVE
        return true
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {

        viewDragHelper.processTouchEvent(event)
        return true
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        measureChildren(widthMeasureSpec, heightMeasureSpec)
    }

    fun createMaskView() {
        if (headerMaskView == null) {
            headerMaskView = WeiXinPullHeaderMaskView(context, null, 0)
            addView(headerMaskView)
        }
    }

    inner class DragHandler : ViewDragHelper.Callback() {
        override fun tryCaptureView(child: View, pointerId: Int): Boolean {
            return child is WeiXinMainLayout;
        }

        override fun onViewDragStateChanged(state: Int) {
            super.onViewDragStateChanged(state)
        }

        /**
         * 设置进度，设置遮罩layout
         */
        override fun onViewPositionChanged(
            changedView: View,
            left: Int,
            top: Int,
            dx: Int,
            dy: Int
        ) {
            createMaskView();
            var programView = getChildAt(0)

            var divide = BigDecimal(top.toString()).divide(
                BigDecimal(measuredHeight - NAVIGAATION_HEIGHT),
                4,
                BigDecimal.ROUND_HALF_UP
            )
            divide = divide.multiply(BigDecimal("100"))

            divide = divide.multiply(BigDecimal("0.002"))
            divide = divide.add(BigDecimal("0.8"))

            if (!isOpen) {
                programView.scaleX = divide.toFloat()
                programView.scaleY = divide.toFloat()
            } else {
                programView.top = paddingTop + (-((measuredHeight - NAVIGAATION_HEIGHT) - top))
            }

            headerMaskView!!.maxHeight = measuredHeight / 3
            headerMaskView!!.layout(0, paddingTop, measuredWidth, top)
            headerMaskView!!.setProgress(
                top.toFloat() / ((measuredHeight - (NAVIGAATION_HEIGHT + paddingTop)) / 3) * 100,
                measuredHeight - (NAVIGAATION_HEIGHT + paddingTop)
            )
            if (top == paddingTop) {
                isOpen = false
            }
            if (top == measuredHeight - NAVIGAATION_HEIGHT) {
                isOpen = true
            }

        }

        override fun onViewCaptured(capturedChild: View, activePointerId: Int) {
            super.onViewCaptured(capturedChild, activePointerId)
            var programView = getChildAt(0)
            programView.top = paddingTop;
        }

        /**
         * 释放
         */
        override fun onViewReleased(releasedChild: View, xvel: Float, yvel: Float) {

            /**
             * 如果已经打开或者释放后小于屏幕三分之一，回到原位
             */
            if (isOpen or (releasedChild.top + paddingTop <= measuredHeight / 3)) {
                viewDragHelper.smoothSlideViewTo(releasedChild, 0, paddingTop);
                ViewCompat.postInvalidateOnAnimation(this@WeiXinMainPullViewGroup);
                return
            }
            viewDragHelper.smoothSlideViewTo(releasedChild, 0, measuredHeight - NAVIGAATION_HEIGHT);
            ViewCompat.postInvalidateOnAnimation(this@WeiXinMainPullViewGroup);
        }

        override fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int {
            if (top <= paddingTop) {
                return paddingTop
            }
            return (child.top + dy / 1.3).toInt();
        }

    }
}

还要增加一个用来填充状态栏的View，他的高度是动态获取的，整体布局是RelativeLayout，因为可以方便的设置中间View在状态下面和在导航栏上面。

class ViewUtils {
    companion object{
        @JvmStatic
        fun getStatusBarHeight(resources: Resources): Int {
            var result = 0
            val resourceId = resources.getIdentifier("status_bar_height", "dimen", "android")
            if (resourceId > 0) {
                result = resources.getDimensionPixelSize(resourceId)
            }
            return result
        }
    }
}

小程序缩放比例值计算

然后要做的就是拖动View，可以借助ViewDragHelper来完成，当拖动会话布局的时候，小程序的布局开始做一个缩放比例动画，这个缩放值我在这是这样做的，因为不可能是从0开始，要从一个基础值开始，这个基础值就是0.8，那么剩下0.2的缩放值，就是从开始下拉算起，到整体的高度的百分比。

比如屏幕高度是1000，下拉到500的时候，那么这个缩放值就是0.1，在加上基础值0.8，计算方式如下，整体高度还要减去导航栏的高度。

   var divide = BigDecimal(top.toString()).divide(BigDecimal(measuredHeight-NAVIGAATION_HEIGHT), 4, BigDecimal.ROUND_HALF_UP)
   divide = divide.multiply(BigDecimal("100"))
   divide = divide.multiply(BigDecimal("0.002" ))
   divide = divide.add(BigDecimal("0.8"))
   if (!isOpen) {
       programView.scaleX = divide.toFloat()
       programView.scaleY = divide.toFloat()
   } else {
       programView.top = paddingTop + (-((measuredHeight - NAVIGAATION_HEIGHT) - top))
   }

这里就注意细节了，下拉的时候，小程序布局是通过缩放呈现的，但是上滑关闭的时，小程序布局是和会话布局同时向上走的。

动画遮罩

这是比较麻烦的一步，就是绘制进度动画，也就是那三个圆点。

这个原点有三种状态，一是出现时从小到大，二是到一定大小后，分离出两个固定大小的圆，但是这两个圆比此时中间的要小，并且和下拉进度慢慢向两边扩撒，三是中间的圆开始缩小，直到和其余两个圈同等大小。

这里就要另一波细节了，当还在屏幕的三分之一下拉时，这个头部遮罩布局整体还是不透明的，但是到屏幕的三分之一时，这个布局的透明度开始从255到0运动。并且到达三分之一的时候，还要振动一下，并且只要振动过了，那么在手指未松开时，再次到达屏幕的三分之一时，不会产生振动。

还有一波细节，状态栏由于使用了View填充，所以，从屏幕三份之一后开始，这个View的透明度也要从255-0开始运动。

完整代码如下。

package com.example.kotlindemo.widget.weixin

import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.os.VibrationEffect
import android.os.Vibrator
import android.util.AttributeSet
import android.util.Log
import android.view.View
import androidx.core.content.ContextCompat
import com.example.kotlindemo.MainActivity
import com.example.kotlindemo.R


class WeiXinPullHeaderMaskView @JvmOverloads constructor(
    context: Context?,
    attrs: AttributeSet?,
    defStyleAttr: Int
) :
    View(context, attrs, defStyleAttr) {

    var isVibrator: Boolean = false;
    var progress: Int = 0;
    var maxHeight: Int = 0;
    private val CIRCLE_MAX_SIZE = 32;
    var parentHeight=0;
    var paint = Paint()
    private val DEFAULT_CIRCLE_SIZE=8f;
    init {
        setBackgroundColor(Color.argb(255 , 239, 239, 239))
        paint.alpha=255;
        paint.color = ContextCompat.getColor(context!!, R.color.circleColor)
        paint.isAntiAlias = true;
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        var value = height.toFloat() / maxHeight

        if (height <= maxHeight / 2) {
            canvas.drawCircle((width / 2).toFloat(), (height / 2).toFloat(), CIRCLE_MAX_SIZE * value, paint)
        } else {
          if (progress<100){
              var diff = (value - 0.5f) * CIRCLE_MAX_SIZE
              canvas.drawCircle(((width / 2).toFloat()-((0.4f-value)*100)), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
              canvas.drawCircle(((width / 2).toFloat()+((0.4f-value)*100)), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
              if ((CIRCLE_MAX_SIZE * 0.5f) - diff<=DEFAULT_CIRCLE_SIZE){
                  canvas.drawCircle((width / 2).toFloat(), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
              }else{
                  canvas.drawCircle((width / 2).toFloat(), (height / 2).toFloat(), (CIRCLE_MAX_SIZE * 0.5f) - diff, paint)
              }

          }else{
              paint.alpha=getAlphaValue();
              canvas.drawCircle((width / 2).toFloat(), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
              canvas.drawCircle((width / 2).toFloat()-((0.4f)*100), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
              canvas.drawCircle((width / 2).toFloat()+(((0.4f)*100)), (height / 2).toFloat(), DEFAULT_CIRCLE_SIZE, paint)
          }
        }

    }
    private fun getAlphaValue():Int{
        val dc=parentHeight/3-ViewUtils.getStatusBarHeight(resources);
        val alpha=((height).toFloat()-dc)/(parentHeight-(dc))
       return 255-(255*alpha).toInt()
    }

    private fun vibrator() {
        var vibrator = context.getSystemService(Context.VIBRATOR_SERVICE) as Vibrator
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
            var createOneShot = VibrationEffect.createOneShot(7, 255)
            vibrator.vibrate(createOneShot)
        } else {
            vibrator.vibrate(7)
        }
    }

    fun setProgress(value: Float,parentHeight:Int) {
        this.progress = value.toInt();
        this.parentHeight=parentHeight;
        if (value >= 100 && !isVibrator) {
            vibrator()
            isVibrator = true;
        }
        if (value < 100) {
            isVibrator = false;
        }
        if (progress>=100){
            setBackgroundColor(Color.argb(getAlphaValue() , 239, 239, 239))
            var mainActivity = context as MainActivity
            mainActivity.changeStatusBackgroundAlphaValue(getAlphaValue())
        }else{
            setBackgroundColor(Color.argb(255, 239, 239, 239))
        }
        invalidate()
    }


}

还有就是这三个原点是始终位于遮罩View中间的，绘制的时候只需要在中间绘制，遮罩View的高度会被外界View所更改。

MainActivity

import android.graphics.Color
import android.os.Build
import android.os.Bundle
import android.view.View
import android.view.Window
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import com.example.kotlindemo.databinding.ActivityMainBinding
import com.example.kotlindemo.widget.weixin.ChatSession
import com.example.kotlindemo.widget.weixin.ChatSessionAdapter
import com.example.kotlindemo.widget.weixin.ViewUtils


class MainActivity : AppCompatActivity() {
    lateinit var binding: ActivityMainBinding;


    fun changeStatusBackgroundAlphaValue(value: Int){
        binding.statusBar.setBackgroundColor(Color.argb(value, 239, 239, 239))
    }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main);

        
        var layoutParams = binding.statusBar.layoutParams
        layoutParams.height=ViewUtils.getStatusBarHeight(resources)
        binding.statusBar.layoutParams=layoutParams
        binding.wxMain.setPadding(0, ViewUtils.getStatusBarHeight(resources), 0, 0)

        if (Build.VERSION.SDK_INT >= 21) {
            val window: Window = window
            window.getDecorView().setSystemUiVisibility(
                View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                        or View.SYSTEM_UI_FLAG_LAYOUT_STABLE or View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR
            )
            window.setStatusBarColor(Color.TRANSPARENT)
        }


        val chatSessions= mutableListOf<ChatSession>()

        for (index in 0 .. 10){
            chatSessions.add(ChatSession("https://img2.baidu.com/it/u=3538084390,1079314259&fm=26&fmt=auto&gp=0.jpg","马云","你来，我把公司给你","上午"))
            chatSessions.add(ChatSession("https://img0.baidu.com/it/u=273576249,1042072491&fm=26&fmt=auto&gp=0.jpg","奥巴马","哥哥在哪呢","上午"))
            chatSessions.add(ChatSession("https://img1.baidu.com/it/u=152902017,4157746361&fm=11&fmt=auto&gp=0.jpg","成龙","马上接你","上午"))
            chatSessions.add(ChatSession("https://img0.baidu.com/it/u=3789809038,289359647&fm=26&fmt=auto&gp=0.jpg","窃瓦辛格","我教你啊","上午"))

        }
        binding.chatList.adapter=ChatSessionAdapter(chatSessions,this)
    }

}

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

    </data>

    <RelativeLayout
        android:background="@drawable/program_background"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">


        <com.example.kotlindemo.widget.weixin.WeiXinMainPullViewGroup
        android:paddingTop="40dp"
            android:layout_above="@+id/navigation"
            android:id="@+id/wx_main"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
          >
            <com.example.kotlindemo.widget.weixin.WeiXinProgram
                android:paddingLeft="30dp"
                android:paddingRight="30dp"
                android:orientation="vertical"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
                <TextView
                    android:textSize="17sp"
                    android:textColor="#C8C8C8"
                    android:gravity="center"
                    android:text="最近"
                    android:layout_width="match_parent"
                    android:layout_height="40dp"></TextView>

                <androidx.cardview.widget.CardView
                    android:background="#424459"
                    app:cardBackgroundColor="#424459"
                    app:cardElevation="0dp"
                    app:cardCornerRadius="8dp"
                    android:layout_width="match_parent"
                    android:layout_height="46dp">
                    <LinearLayout
                        android:gravity="center"
                        android:layout_width="match_parent"
                        android:layout_height="match_parent">
                        <TextView
                            android:textSize="15sp"
                            android:textColor="#C8C8C8"
                            android:text="搜索小程序"
                            android:gravity="center"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"></TextView>
                    </LinearLayout>
                </androidx.cardview.widget.CardView>
                <com.example.kotlindemo.widget.weixin.ProgramGridLayout
                    android:layout_marginTop="20dp"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content">

                </com.example.kotlindemo.widget.weixin.ProgramGridLayout>
                <com.example.kotlindemo.widget.weixin.ProgramGridLayout
                    android:layout_marginTop="20dp"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content">

                </com.example.kotlindemo.widget.weixin.ProgramGridLayout>
            </com.example.kotlindemo.widget.weixin.WeiXinProgram>
            <com.example.kotlindemo.widget.weixin.WeiXinMainLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical">
                <RelativeLayout
                    android:layout_width="match_parent"
                    android:layout_height="44dp"
                    android:background="@color/navigation_color">

                    <TextView
                        android:textStyle="bold"
                        android:textSize="16sp"
                        android:textColor="#000000"
                        android:layout_centerInParent="true"
                        android:gravity="center"
                        android:text="微信(323)"
                        android:layout_width="wrap_content"
                        android:layout_height="match_parent"></TextView>
                    <ImageView
                        android:layout_marginRight="45dp"
                        android:scaleType="center"
                        android:layout_centerVertical="true"
                        android:layout_alignParentRight="true"
                        android:src="@drawable/ic_search"
                        android:layout_width="28dp"
                        android:layout_height="28dp"></ImageView>
                    <ImageView
                        android:layout_marginRight="10dp"
                        android:scaleType="center"
                        android:layout_centerVertical="true"
                        android:layout_alignParentRight="true"
                        android:src="@drawable/ic_add"
                        android:layout_width="28dp"
                        android:layout_height="28dp">

                    </ImageView>
                </RelativeLayout>
                <com.example.kotlindemo.widget.weixin.WeiXinChatSessionListView
                    android:paddingLeft="15dp"

                    android:paddingRight="15dp"
                    android:dividerHeight="10dp"
                    android:id="@+id/chat_list"
                    android:background="#FBFAFA"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent">

                </com.example.kotlindemo.widget.weixin.WeiXinChatSessionListView>

            </com.example.kotlindemo.widget.weixin.WeiXinMainLayout>

        </com.example.kotlindemo.widget.weixin.WeiXinMainPullViewGroup>

        <LinearLayout
            android:background="@color/navigation_color"
            android:orientation="vertical"
            android:id="@+id/navigation"
            android:layout_alignParentBottom="true"
            android:layout_width="match_parent"
            android:layout_height="60dp">
        </LinearLayout>
        <View
            android:background="@color/navigation_color"
            android:id="@+id/status_bar"
            android:layout_width="match_parent"
            android:layout_height="100dp"></View>
    </RelativeLayout>
</layout>