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：

这是 Android Window 应用的第一篇，系列文章目录如下：

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 = 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 {

/**

*

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。