本文以业务应用为出发点，从零开始抽象一个浮窗工具类，它用于在任意业务界面上展示悬浮窗。它可以同时管理多个浮窗，而且浮窗可以响应触摸事件，可拖拽，有贴边动画。

文中实例代码使用 kotlin 编写，kotlin 系列教程可以点击这里

效果如下：

float window

这是 Android Window 应用的第一篇，系列文章目录如下：

1. 悬浮窗的一种实现 | Android悬浮窗Window应用
2. 下沉式通知的一种实现 | Android悬浮窗Window应用

显示浮窗

原生ViewManager接口提供了向窗口添加并操纵View的方法：

public interface ViewManager{
    //'向窗口添加视图'
    public void addView(View view, ViewGroup.LayoutParams params);
    //'更新窗口中视图'
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    //'移除窗口中视图'
    public void removeView(View view);
}

使用这个接口显示窗口的模版代码如下：

//'解析布局文件为视图'
val windowView = LayoutInflater.from(context).inflate(R.id.window_view, null)
//'获取WindowManager系统服务'
val windowManager = context.getSystemService(Context.WINDOW_SERVICE) as WindowManager
//'构建窗口布局参数'
WindowManager.LayoutParams().apply {
    type = WindowManager.LayoutParams.TYPE_APPLICATION
    width = WindowManager.LayoutParams.WRAP_CONTENT
    height = WindowManager.LayoutParams.WRAP_CONTENT
    gravity = Gravity.START or Gravity.TOP
    x = 0
    y = 0
}.let { layoutParams->
    //'将视图添加到窗口'
    windowManager.addView(windowView, layoutParams)
}

• 上述代码在当前界面的左上角显示R.id.window_view.xml中定义的布局。
• 为避免重复，将这段代码抽象成一个函数，其中窗口视图内容和展示位置会随着需求而变，遂将其参数化：

object FloatWindow{
    private var context: Context? = null
    //'当前窗口参数'
    var windowInfo: WindowInfo? = null
    
    //'把和Window布局有关的参数打包成一个内部类'
    class WindowInfo(var view: View?) {
        var layoutParams: WindowManager.LayoutParams? = null
        //'窗口宽'
        var width: Int = 0
        //'窗口高'
        var height: Int = 0
        //'窗口中是否有视图'
        fun hasView() = view != null && layoutParams != null
        //'窗口中视图是否有父亲'
        fun hasParent() = hasView() && view?.parent != null
    }
    
    //'显示窗口'
    fun show(
        context: Context,
        windowInfo: WindowInfo?,
        x: Int = windowInfo?.layoutParams?.x.value(),
        y: Int = windowInfo?.layoutParams?.y.value(),
    ) {
        if (windowInfo == null) { return }
        if (windowInfo.view == null) { return }
        this.windowInfo = windowInfo
        this.context = context
        //'创建窗口布局参数'
        windowInfo.layoutParams = createLayoutParam(x, y)
        //'显示窗口'
        if (!windowInfo.hasParent().value()) {
            val windowManager = this.context?.getSystemService(Context.WINDOW_SERVICE) as WindowManager
            windowManager.addView(windowInfo.view, windowInfo.layoutParams)
        }
    }
    
    //'创建窗口布局参数'
    private fun createLayoutParam(x: Int, y: Int): WindowManager.LayoutParams {
        if (context == null) { return WindowManager.LayoutParams() }
        return WindowManager.LayoutParams().apply {
            //'该类型不需要申请权限'
            type = WindowManager.LayoutParams.TYPE_APPLICATION
            format = PixelFormat.TRANSLUCENT
            flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE or WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS
            gravity = Gravity.START or Gravity.TOP
            width = windowInfo?.width.value()
            height = windowInfo?.height.value()
            this.x = x
            this.y = y
        }
    }
    
    //'为空Int提供默认值'
    fun Int?.value() = this ?: 0
}

• 将FloatWindow声明成了单例，目的是在 app 整个生命周期，任何界面都可以方便地显示浮窗。
• 为了方便统一管理窗口的参数，抽象了内部类WindowInfo
• 现在就可以像这样在屏幕左上角显示一个浮窗了：

val windowView = LayoutInflater.from(context).inflate(R.id.window_view, null)
WindowInfo(windowView).apply{
    width = 100
    height = 100
}.let{ windowInfo ->
    FloatWindow.show(context, windowInfo, 0, 0)
}

浮窗背景色

产品要求当浮窗显示时，屏幕变暗。设置WindowManager.LayoutParams.FLAG_DIM_BEHIND标签配合dimAmount就能轻松实现：

object FloatWindow{
    //当前窗口参数
    var windowInfo: WindowInfo? = null
    
    private fun createLayoutParam(x: Int, y: Int): WindowManager.LayoutParams {
        if (context == null) { return WindowManager.LayoutParams() }

        return WindowManager.LayoutParams().apply {
            type = WindowManager.LayoutParams.TYPE_APPLICATION
            format = PixelFormat.TRANSLUCENT
            flags =
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE or
                WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS or
                //'设置浮窗背景变暗'
                WindowManager.LayoutParams.FLAG_DIM_BEHIND
            //'设置默认变暗程度为0，即不变暗，1表示全黑'
            dimAmount = 0f
            gravity = Gravity.START or Gravity.TOP
            width = windowInfo?.width.value()
            height = windowInfo?.height.value()
            this.x = x
            this.y = y
        }
    }
    
    //'供业务界面在需要的时候调整浮窗背景亮暗'
    fun setDimAmount(amount:Float){
        windowInfo?.layoutParams?.let { it.dimAmount = amount }
    }
}

设置浮窗点击事件

为浮窗设置点击事件等价于为浮窗视图设置点击事件，但如果直接对浮窗视图使用setOnClickListener()的话，浮窗的触摸事件就不会被响应，那拖拽就无法实现。所以只能从更底层的触摸事件着手：

object FloatWindow : View.OnTouchListener{ 
    //'显示窗口'
    fun show(
        context: Context,
        windowInfo: WindowInfo?,
        x: Int = windowInfo?.layoutParams?.x.value(),
        y: Int = windowInfo?.layoutParams?.y.value(),
    ) {
        if (windowInfo == null) { return }
        if (windowInfo.view == null) { return }
        this.windowInfo = windowInfo
        this.context = context
        //'为浮窗视图设置触摸监听器'
        windowInfo.view?.setOnTouchListener(this)
        windowInfo.layoutParams = createLayoutParam(x, y)
        if (!windowInfo.hasParent().value()) {
            val windowManager = this.context?.getSystemService(Context.WINDOW_SERVICE) as WindowManager
            windowManager.addView(windowInfo.view, windowInfo.layoutParams)
        }
    }
    
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        return false
    }
}

• 在onTouch(v: View, event: MotionEvent)中可以拿到更详细的触摸事件，比如ACTION_DOWN，ACTION_MOVE、ACTION_UP。这方便了拖拽的实现，但点击事件的捕获变得复杂，因为需要定义上述三个 ACTION 以怎样的序列出现时才判定为点击事件。幸好GestureDetector为我们做了这件事：

public class GestureDetector {
    public interface OnGestureListener {
        //'ACTION_DOWN事件'
        boolean onDown(MotionEvent e);
        //'单击事件'
        boolean onSingleTapUp(MotionEvent e);
        //'拖拽事件'
        boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);
        ...
    }
}

构建GestureDetector实例并将MotionEvent传递给它就能将触摸事件解析成感兴趣的上层事件：

object FloatWindow : View.OnTouchListener{ 
    private var gestureDetector: GestureDetector = GestureDetector(context, GestureListener())
    private var clickListener: WindowClickListener? = null
    private var lastTouchX: Int = 0
    private var lastTouchY: Int = 0
    
    //'为浮窗设置点击监听器'
    fun setClickListener(listener: WindowClickListener) {
        clickListener = listener
    }
    
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        //'将触摸事件传递给 GestureDetector 解析'
        gestureDetector.onTouchEvent(event)
        return true
    }
    
    //'记忆起始触摸点坐标'
    private fun onActionDown(event: MotionEvent) {
        lastTouchX = event.rawX.toInt()
        lastTouchY = event.rawY.toInt()
    }

    private class GestureListener : GestureDetector.OnGestureListener {
        //'记忆起始触摸点坐标'
        override fun onDown(e: MotionEvent): Boolean {
            onActionDown(e)
            return false
        }
        
        override fun onSingleTapUp(e: MotionEvent): Boolean {
            //'点击事件发生时，调用监听器'
            return clickListener?.onWindowClick(windowInfo) ?: false
        }

        ...
    }
    
    //'浮窗点击监听器'
    interface WindowClickListener {
        fun onWindowClick(windowInfo: WindowInfo?): Boolean
    }
}

拖拽浮窗

ViewManager提供了updateViewLayout(View view, ViewGroup.LayoutParams params)用于更新浮窗位置，所以只需监听ACTION_MOVE事件并实时更新浮窗视图位置就可实现拖拽。ACTION_MOVE事件被GestureDetector解析成OnGestureListener.onScroll()回调：

object FloatWindow : View.OnTouchListener{ 
    private var gestureDetector: GestureDetector = GestureDetector(context, GestureListener())
    private var lastTouchX: Int = 0
    private var lastTouchY: Int = 0
    
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        //'将触摸事件传递给GestureDetector解析'
        gestureDetector.onTouchEvent(event)
        return true
    }

    private class GestureListener : GestureDetector.OnGestureListener {
        override fun onDown(e: MotionEvent): Boolean {
            onActionDown(e)
            return false
        }

        override fun onScroll(e1: MotionEvent,e2: MotionEvent,distanceX: Float,distanceY:Float): Boolean {
            //'响应手指滚动事件'
            onActionMove(e2)
            return true
        }
    }
    
    private fun onActionMove(event: MotionEvent) {
        //'获取当前手指坐标'
        val currentX = event.rawX.toInt()
        val currentY = event.rawY.toInt()
        //'获取手指移动增量'
        val dx = currentX - lastTouchX
        val dy = currentY - lastTouchY
        //'将移动增量应用到窗口布局参数上'
        windowInfo?.layoutParams!!.x += dx
        windowInfo?.layoutParams!!.y += dy
        val windowManager = context?.getSystemService(Context.WINDOW_SERVICE) as WindowManager
        var rightMost = screenWidth - windowInfo?.layoutParams!!.width
        var leftMost = 0
        val topMost = 0
        val bottomMost = screenHeight - windowInfo?.layoutParams!!.height - getNavigationBarHeight(context)
        //'将浮窗移动区域限制在屏幕内'
        if (windowInfo?.layoutParams!!.x < leftMost) {
            windowInfo?.layoutParams!!.x = leftMost
        }
        if (windowInfo?.layoutParams!!.x > rightMost) {
            windowInfo?.layoutParams!!.x = rightMost
        }
        if (windowInfo?.layoutParams!!.y < topMost) {
            windowInfo?.layoutParams!!.y = topMost
        }
        if (windowInfo?.layoutParams!!.y > bottomMost) {
            windowInfo?.layoutParams!!.y = bottomMost
        }
        //'更新浮窗位置'
        windowManager.updateViewLayout(windowInfo?.view, windowInfo?.layoutParams)
        lastTouchX = currentX
        lastTouchY = currentY
    }
}

浮窗自动贴边

新的需求来了，拖拽浮窗松手后，需要自动贴边。

把贴边理解成一个水平位移动画。在松手时求出动画起点和终点横坐标，利用动画值不断更新浮窗位置：：

object FloatWindow : View.OnTouchListener{ 
    private var gestureDetector: GestureDetector = GestureDetector(context, GestureListener())
    private var lastTouchX: Int = 0
    private var lastTouchY: Int = 0
    //'贴边动画'
    private var weltAnimator: ValueAnimator? = null
    
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        //'将触摸事件传递给GestureDetector解析'
        gestureDetector.onTouchEvent(event)
        //'处理ACTION_UP事件'
        val action = event.action
        when (action) {
            MotionEvent.ACTION_UP -> onActionUp(event, screenWidth, windowInfo?.width ?: 0)
            else -> {
            }
        }
        return true
    }
    
    private fun onActionUp(event: MotionEvent, screenWidth: Int, width: Int) {
        if (!windowInfo?.hasView().value()) { return }
        //'记录抬手横坐标'
        val upX = event.rawX.toInt()
        //'贴边动画终点横坐标'
        val endX = if (upX > screenWidth / 2) {
            screenWidth - width
        } else {
            0
        }

        //'构建贴边动画'
        if (weltAnimator == null) {
            weltAnimator = ValueAnimator.ofInt(windowInfo?.layoutParams!!.x, endX).apply {
                interpolator = LinearInterpolator()
                duration = 300
                addUpdateListener { animation ->
                    val x = animation.animatedValue as Int
                    if (windowInfo?.layoutParams != null) {
                        windowInfo?.layoutParams!!.x = x
                    }
                    val windowManager = context?.getSystemService(Context.WINDOW_SERVICE) as WindowManager
                    //'更新窗口位置'
                    if (windowInfo?.hasParent().value()) {
                        windowManager.updateViewLayout(windowInfo?.view, windowInfo?.layoutParams)
                    }
                }
            }
        }
        weltAnimator?.setIntValues(windowInfo?.layoutParams!!.x, endX)
        weltAnimator?.start()
    }
    
    //为空Boolean提供默认值
    fun Boolean?.value() = this ?: false
}

• GestureDetector解析后ACTION_UP事件被吞掉了，所以只能在onTouch()中截获它。
• 根据抬手横坐标和屏幕中点横坐标的大小关系，来决定浮窗贴向左边还是右边。

管理多个浮窗

若 app 的不同业务界面同时需要显示浮窗：进入 界面A 时显示 浮窗A，然后它被拖拽到右下角，退出 界面A 进入 界面B，显示浮窗B，当再次进入 界面A 时，期望还原上次离开时的浮窗A的位置。

当前FloatWindow中用windowInfo成员存储单个浮窗参数，为了同时管理多个浮窗，需要将所有浮窗参数保存在Map结构中用 tag 区分：

object FloatWindow : View.OnTouchListener {
    //'浮窗参数容器'
    private var windowInfoMap: HashMap<String, WindowInfo?> = HashMap()
    //'当前浮窗参数'
    var windowInfo: WindowInfo? = null
    
    //'显示浮窗'
    fun show(
        context: Context,
        //'浮窗标签'
        tag: String,
        //'若不提供浮窗参数则从参数容器中获取该tag上次保存的参数'
        windowInfo: WindowInfo? = windowInfoMap[tag],
        x: Int = windowInfo?.layoutParams?.x.value(),
        y: Int = windowInfo?.layoutParams?.y.value()
    ) {
        if (windowInfo == null) { return }
        if (windowInfo.view == null) { return }
        //'更新当前浮窗参数'
        this.windowInfo = windowInfo
        //'将浮窗参数存入容器'
        windowInfoMap[tag] = windowInfo
        windowInfo.view?.setOnTouchListener(this)
        this.context = context
        windowInfo.layoutParams = createLayoutParam(x, y)
        if (!windowInfo.hasParent().value()) {
            val windowManager =this.context?.getSystemService(Context.WINDOW_SERVICE) as WindowManager
            windowManager.addView(windowInfo.view, windowInfo.layoutParams)
        }
    }
}

在显示浮窗时，增加tag标签参数用以唯一标识浮窗，并且为windowInfo提供默认参数，当恢复原有浮窗时，可以不提供windowInfo参数，FloatWindow就会去windowInfoMap中根据给定tag寻找对应windowInfo。

监听浮窗界外点击事件

新的需求来了，点击浮窗时，贴边的浮窗像抽屉一样展示，点击浮窗以外区域时，抽屉收起。

刚开始接到这个新需求时，没什么思路。转念一想PopupWindow有一个setOutsideTouchable()：

public class PopupWindow {
    /**
     * <p>Controls whether the pop-up will be informed of touch events outside
     * of its window. 
     *
     * @param touchable true if the popup should receive outside
     * touch events, false otherwise
     */
    public void setOutsideTouchable(boolean touchable) {
        mOutsideTouchable = touchable;
    }
}

该函数用于设置是否允许 window 边界外的触摸事件传递给 window。跟踪mOutsideTouchable变量应该就能找到更多线索：

public class PopupWindow {
    private int computeFlags(int curFlags) {
        curFlags &= ~(
                WindowManager.LayoutParams.FLAG_IGNORE_CHEEK_PRESSES |
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
                WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE |
                WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH |
                WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS |
                WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM |
                WindowManager.LayoutParams.FLAG_SPLIT_TOUCH);
        ...
        //'如果界外可触摸，则将FLAG_WATCH_OUTSIDE_TOUCH赋值给flag'
        if (mOutsideTouchable) {
            curFlags |= WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;
        }
        ...
    }
}

继续往上跟踪computeFlags()调用的地方：

public class PopupWindow {
    protected final WindowManager.LayoutParams createPopupLayoutParams(IBinder token) {
        final WindowManager.LayoutParams p = new WindowManager.LayoutParams();

        p.gravity = computeGravity();
        //'计算窗口布局参数flag属性并赋值'
        p.flags = computeFlags(p.flags);
        p.type = mWindowLayoutType;
        p.token = token;
        ...
    }
}

而createPopupLayoutParams()会在窗口显示的时候被调用：

public class PopupWindow {
    public void showAtLocation(IBinder token, int gravity, int x, int y) {
        if (isShowing() || mContentView == null) { return; }
        TransitionManager.endTransitions(mDecorView);
        detachFromAnchor();
        mIsShowing = true;
        mIsDropdown = false;
        mGravity = gravity;

        //'构建窗口布局参数'
        final WindowManager.LayoutParams p = createPopupLayoutParams(token);
        preparePopup(p);
        p.x = x;
        p.y = y;
        invokePopup(p);
    }
}

想在源码中继续搜索，但到FLAG_WATCH_OUTSIDE_TOUCH，线索就断了。现在只知道为了让界外点击事件传递给 window，必须为布局参数设置FLAG_WATCH_OUTSIDE_TOUCH。但事件响应逻辑应该写在哪里？

当调用PopupWindow.setOutsideTouchable(true)，在窗口界外点击后，窗口会消失。这必然是调用了dismiss()，沿着dismiss()的调用链往上找一定能找到界外点击事件的响应逻辑：

public class PopupWindow {
    //'窗口根视图'
    private class PopupDecorView extends FrameLayout {
    
        //'窗口根视图触摸事件'
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            final int x = (int) event.getX();
            final int y = (int) event.getY();

            if ((event.getAction() == MotionEvent.ACTION_DOWN)
                    && ((x < 0) || (x >= getWidth()) || (y < 0) || (y >= getHeight()))) {
                dismiss();
                return true;
            //'如果发生了界外触摸事件则解散窗口'
            } else if (event.getAction() == MotionEvent.ACTION_OUTSIDE) {
                dismiss();
                return true;
            } else {
                return super.onTouchEvent(event);
            }
        }
    }
}

所以只需要在窗口根视图的触摸事件回调中捕获ACTION_OUTSIDE即可：

object FloatWindow : View.OnTouchListener {
    //'界外触摸事件回调'
    private var onTouchOutside: (() -> Unit)? = null
    
    //'设置是否响应界外点击事件'
    fun setOutsideTouchable(enable: Boolean, onTouchOutside: (() -> Unit)? = null) {
        windowInfo?.layoutParams?.let { layoutParams ->
            layoutParams.flags = layoutParams.flags or WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH
            this.onTouchOutside = onTouchOutside
        }
    }
    
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        //'界外触摸事件处理'
        if (event.action == MotionEvent.ACTION_OUTSIDE) {
            onTouchOutside?.invoke()
            return true
        }

        //'点击和拖拽事件处理'
        gestureDetector.onTouchEvent(event).takeIf { !it }?.also {
            //there is no ACTION_UP event in GestureDetector
            val action = event.action
            when (action) {
                MotionEvent.ACTION_UP -> onActionUp(event, screenWidth, windowInfo?.width ?: 0)
                else -> {
                }
            }
        }
        return true
    }
}

talk is cheap, show me the code

实例代码隐藏了不重要的细节，完整代码可点击上面链接。