Android懸浮窗原理解析(Window)[源碼]
阿新 • • 發佈：2018-07-07
tco inflate 情況 tint input tdi scree list 接收
懸浮窗，在大多數應用中還是很少見的，目前我們接觸到的懸浮窗，差不多都是一些系統級的應用軟件，例如：360安全衛士，騰訊手機管家等；在某些服務行業如金融，餐飲等，也會在應用中添加懸浮窗，例如：美團的偷紅包，博聞金融快捷聯系等。但兩種懸浮窗還是有區別的：
- 系統懸浮窗：所有界面都會展示，包括主屏、鎖屏
- 應用懸浮窗：只在應用Activity中展示。
一、窗口Window
在了解懸浮窗之前，首先我們需要認識一下Android窗口Window。Android Framework將窗口分為三個類型：
- 應用窗口：所謂應用窗口指的就是該窗口對應一個Activity，因此，要創建應用窗口就必須在Activity中完成了。
- 子窗口：所謂子窗口指的是必須依附在某個父窗口之上，比如PopWindow，Dialog。
- 系統窗口：所謂系統窗口指的是由系統進程創建，不依賴於任何應用或者不依附在任何父窗口之上，如：Toast,來電窗口等。
Framework定義了三種窗口類型，這三種類型定義在WindowManager的內部類LayoutParams中，WindowManager將這三種類型 進行了細化，把每一種類型都用一個int常量來表示，這些常量代表窗口所在的層，WindowManagerService在進行窗口疊加的時候，會按照常量的大小分配不同的層，常量值越大，代表位置越靠上面，所以我們可以猜想一下，應用程序Window的層值常量要小於子Window的層值常量，子Window的層值常量要小於系統Window的層值常量。Window的層級關系如下所示。
- 應用窗口：層級範圍是1~99
- 子窗口：層級範圍是1000~1999
- 系統窗口：層級範圍是2000~2999
1.各級別type值在WindowManager中的定義分別為：
i.應用窗口（1~99）
//第一個應用窗口
public static final int FIRST_APPLICATION_WINDOW = 1;
//所有程序窗口的base窗口，其他應用程序窗口都顯示在它上面
public static final int TYPE_BASE_APPLICATION = 1;
//所有Activity的窗口，只能配合Activity在當前APP使用
public static final int TYPE_APPLICATION = 2;
//目標應用窗口未啟動之前的那個窗口
public static final int TYPE_APPLICATION_STARTING = 3;
//最後一個應用窗口
public static final int LAST_APPLICATION_WINDOW = 99; ii.子窗口（1000~1999）
//第一個子窗口
public static final int FIRST_SUB_WINDOW = 1000;
// 面板窗口，顯示於宿主窗口的上層,只能配合Activity在當前APP使用
public static final int TYPE_APPLICATION_PANEL = FIRST_SUB_WINDOW;
// 媒體窗口（例如視頻），顯示於宿主窗口下層
public static final int TYPE_APPLICATION_MEDIA = FIRST_SUB_WINDOW+1;
// 應用程序窗口的子面板，只能配合Activity在當前APP使用(PopupWindow默認就是這個Type)
public static final int TYPE_APPLICATION_SUB_PANEL = FIRST_SUB_WINDOW+2;
//對話框窗口,只能配合Activity在當前APP使用
public static final int TYPE_APPLICATION_ATTACHED_DIALOG = FIRST_SUB_WINDOW+3;
//
public static final int TYPE_APPLICATION_MEDIA_OVERLAY = FIRST_SUB_WINDOW+4;
//最後一個子窗口
public static final int LAST_SUB_WINDOW = 1999;iii.系統窗口（2000~2999）
//系統窗口，非應用程序創建
public static final int FIRST_SYSTEM_WINDOW = 2000;
//狀態欄，只能有一個狀態欄，位於屏幕頂端，其他窗口都位於它下方
public static final int TYPE_STATUS_BAR = FIRST_SYSTEM_WINDOW;
//搜索欄，只能有一個搜索欄，位於屏幕上方
public static final int TYPE_SEARCH_BAR = FIRST_SYSTEM_WINDOW+1;
//
//電話窗口，它用於電話交互（特別是呼入），置於所有應用程序之上，狀態欄之下,屬於懸浮窗(並且給一個Activity的話按下HOME鍵會出現看不到桌面上的圖標異常情況)
public static final int TYPE_PHONE = FIRST_SYSTEM_WINDOW+2;
//
//系統警告提示窗口，出現在應用程序窗口之上,屬於懸浮窗, 但是會被禁止
public static final int TYPE_SYSTEM_ALERT = FIRST_SYSTEM_WINDOW+3;
//
//信息窗口，用於顯示Toast, 不屬於懸浮窗, 但有懸浮窗的功能, 缺點是在Android2.3上無法接收點擊事件
public static final int TYPE_TOAST = FIRST_SYSTEM_WINDOW+5;
//
public static final int TYPE_KEYGUARD = FIRST_SYSTEM_WINDOW+4;
//鎖屏窗口
public static final int TYPE_KEYGUARD = FIRST_SYSTEM_WINDOW+4;
//系統頂層窗口，顯示在其他一切內容之上，此窗口不能獲得輸入焦點，否則影響鎖屏
public static final int TYPE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+6;
//電話優先，當鎖屏時顯示，此窗口不能獲得輸入焦點，否則影響鎖屏
public static final int TYPE_PRIORITY_PHONE = FIRST_SYSTEM_WINDOW+7;
//系統對話框窗口
public static final int TYPE_SYSTEM_DIALOG = FIRST_SYSTEM_WINDOW+8;
//鎖屏時顯示的對話框
public static final int TYPE_KEYGUARD_DIALOG = FIRST_SYSTEM_WINDOW+9;
//系統內部錯誤提示，顯示在任何窗口之上
public static final int TYPE_SYSTEM_ERROR = FIRST_SYSTEM_WINDOW+10;
//內部輸入法窗口，顯示於普通UI之上，應用程序可重新布局以免被此窗口覆蓋
public static final int TYPE_INPUT_METHOD = FIRST_SYSTEM_WINDOW+11;
//內部輸入法對話框，顯示於當前輸入法窗口之上
public static final int TYPE_INPUT_METHOD_DIALOG= FIRST_SYSTEM_WINDOW+12;
//墻紙窗口
public static final int TYPE_WALLPAPER = FIRST_SYSTEM_WINDOW+13;
//狀態欄的滑動面板
public static final int TYPE_STATUS_BAR_PANEL = FIRST_SYSTEM_WINDOW+14;
//安全系統覆蓋窗口，這些窗戶必須不帶輸入焦點，否則會幹擾鍵盤
public static final int TYPE_SECURE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+15;
//最後一個系統窗口
public static final int LAST_SYSTEM_WINDOW = 2999;2.窗口flags顯示屬性在WindowManager中也有定義：
//窗口特征標記
public int flags;
//當該window對用戶可見的時候，允許鎖屏
public static final int FLAG_ALLOW_LOCK_WHILE_SCREEN_ON = 0x00000001;
//窗口後面的所有內容都變暗
public static final int FLAG_DIM_BEHIND = 0x00000002;
//Flag：窗口後面的所有內容都變模糊
public static final int FLAG_BLUR_BEHIND = 0x00000004;
//窗口不能獲得焦點
public static final int FLAG_NOT_FOCUSABLE = 0x00000008;
//窗口不接受觸摸屏事件
public static final int FLAG_NOT_TOUCHABLE = 0x00000010;
//即使在該window在可獲得焦點情況下，允許該窗口之外的點擊事件傳遞到當前窗口後面的的窗口去
public static final int FLAG_NOT_TOUCH_MODAL = 0x00000020;
//當手機處於睡眠狀態時，如果屏幕被按下，那麽該window將第一個收到觸摸事件
public static final int FLAG_TOUCHABLE_WHEN_WAKING = 0x00000040;
//當該window對用戶可見時，屏幕出於常亮狀態
public static final int FLAG_KEEP_SCREEN_ON = 0x00000080;
//：讓window占滿整個手機屏幕，不留任何邊界
public static final int FLAG_LAYOUT_IN_SCREEN = 0x00000100;
//允許窗口超出整個手機屏幕
public static final int FLAG_LAYOUT_NO_LIMITS = 0x00000200;
//window全屏顯示
public static final int FLAG_FULLSCREEN = 0x00000400;
//恢復window非全屏顯示
public static final int FLAG_FORCE_NOT_FULLSCREEN = 0x00000800;
//開啟窗口抖動
public static final int FLAG_DITHER = 0x00001000;
//安全內容窗口，該窗口顯示時不允許截屏
public static final int FLAG_SECURE = 0x00002000;
//鎖屏時顯示該窗口
public static final int FLAG_SHOW_WHEN_LOCKED = 0x00080000;
//系統的墻紙顯示在該窗口之後
public static final int FLAG_SHOW_WALLPAPER = 0x00100000;
//當window被顯示的時候，系統將把它當做一個用戶活動事件，以點亮手機屏幕
public static final int FLAG_TURN_SCREEN_ON = 0x00200000;
//該窗口顯示，消失鍵盤
public static final int FLAG_DISMISS_KEYGUARD = 0x00400000;
//當該window在可以接受觸摸屏情況下，讓因在該window之外，而發送到後面的window的觸摸屏可以支持split touch
public static final int FLAG_SPLIT_TOUCH = 0x00800000;
//對該window進行硬件加速，該flag必須在Activity或Dialog的Content View之前進行設置
public static final int FLAG_HARDWARE_ACCELERATED = 0x01000000;
//讓window占滿整個手機屏幕，不留任何邊界
public static final int FLAG_LAYOUT_IN_OVERSCAN = 0x02000000;
//透明狀態欄
public static final int FLAG_TRANSLUCENT_STATUS = 0x04000000;
//透明導航欄
3.添加View到Window的流程代碼：
contactView = new ContactView(mContext);
if (layoutParams == null) www.yongshiyule178.com {
layoutParams = new WindowManager.LayoutParams();
layoutParams.width = contactView.width;
layoutParams.height = contactView.height;
layoutParams.x += ScreenSizeUtil.getScreenWidth(www.078881.cn );
layoutParams.y += ScreenSizeUtil.getScreenHeight(www.345608.cn/) - ScreenSizeUtil.dp2px(150);
layoutParams.gravity = www.taohuayuan178.com Gravity.TOP | Gravity.LEFT;
if (Build.VERSION.SDK_INT > 18 && Build.VERSION.SDK_INT < www.feifanyule.cn 23) {
layoutParams.type = WindowManager.LayoutParams.TYPE_TOAST;//Type設置
} else {
layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION;
}
layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;//Flags設置,窗口屬性
layoutParams.format = PixelFormat.RGBA_8888;
懸浮窗添加原理：View添加到Window源碼解析
Window在Android系統中十分重要，其Activity，Dialog的創建都離不開Window.具體Activity，Dialog是怎麽添加到Window上的，詳情如：
Activity的加載流程;
Dialog加載繪制流程
二、兩種懸浮窗
在前言中已說到，懸浮窗在app中，分為兩種：系統級別和應用級別。其中系統級別可以在任何界面展示，包括主屏、鎖屏（看需要），應用級別只在應用中展示。通過上面對Window的認識，我們可以知道實現方式：
- 系統級別可以通過type設置為：TYPE_TOAST、TYPE_PHONE、TYPE_SYSTEM_ALERT；
- 應用級別可以通過type設置為：TYPE_APPLICATION、TYPE_APPLICATION_ATTACHED_DIALOG；
懸浮窗添加流程：
WindowManager.addView -> ViewRootImpl.setView -> WindowSession.addToDisplay(AIDL進行IPC) -> WindowManagerService.addWindow() -> ViewRootImpl.setView
1.系統懸浮窗
對於系統級別的懸浮窗來說，不同的設置，不同的Android版本，需要權限和交互都不同。通過閱讀源碼android4.4知：
android 7.1.1的addWindow方法為：
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, InputChannel outInputChannel) {
int[] appOp = new int[1];
int res = mPolicy.checkAddPermission(attrs, appOp);
if (res != WindowManagerGlobal.ADD_OKAY) {
return res;
}
......
final int type = attrs.type;
......
} else if (type == TYPE_TOAST) {//android 7.1.1 添加代碼（其他版本無）
// Apps targeting SDK above N MR1 cannot arbitrary add toast windows.
addToastWindowRequiresToken = doesAddToastWindowRequireToken(attrs.packageName,
callingUid, attachedWindow);
if (addToastWindowRequiresToken && token.windowType != TYPE_TOAST) {
Slog.w(TAG_WM, "Attempted to add a toast window with bad token "
+ attrs.token + ". Aborting.");
return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
}
}....
synchronized(mWindowMap) {
......
mPolicy.adjustWindowParamsLw(win.mAttrs);
權限檢查checkAddPermission(www.tiaotiaoylzc.com)方法：
//權限檢查
@Override
public int checkAddPermission(WindowManager.www.chaoyueyule.com LayoutParams attrs, int[] outAppOp) {
int type = attrs.type;
outAppOp[0] = AppOpsManager.OP_NONE;
if (type < WindowManager.LayoutParams.FIRST_SYSTEM_WINDOW
|| type > WindowManager.LayoutParams.LAST_SYSTEM_WINDOW) {
return WindowManagerGlobal.ADD_OKAY;
}
String permission = null;
switch (type) {
case TYPE_TOAST:
// XXX right now the app process has complete control over
// this... should introduce www.00534.cn a token to let the system
// monitor/control what they are doing.
break;
case TYPE_DREAM:
case TYPE_INPUT_METHOD:
case TYPE_WALLPAPER:
case TYPE_PRIVATE_PRESENTATION:
// The window manager www.dongfan178.com will check these.
break;
case TYPE_PHONE:
case TYPE_PRIORITY_PHONE:
case TYPE_SYSTEM_ALERT:
case TYPE_SYSTEM_ERROR:
case TYPE_SYSTEM_OVERLAY:
permission = android.Manifest.permission.SYSTEM_ALERT_WINDOW;
outAppOp[0] = AppOpsManager.OP_SYSTEM_ALERT_WINDOW;
break;
default:
permission = android.Manifest.permission.INTERNAL_SYSTEM_WINDOW;
}
if (permission != null) {
if (mContext.checkCallingOrSelfPermission(permission)
!= PackageManager.PERMISSION_GRANTED) {
return WindowManagerGlobal.ADD_PERMISSION_DENIED;
}
}
return WindowManagerGlobal.ADD_OKAY;
window的flags屬性添加adjustWindowParamsLw()方法
//window的flags屬性添加
//Android 2.0 - 2.3.7 PhoneWindowManager
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
case TYPE_TOAST:
// These types of windows can‘t receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
break;
}
}
//Android 4.0.1 - 4.3.1 PhoneWindowManager
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
case TYPE_TOAST:
// These types of windows can‘t receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
attrs.flags &= ~WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;
break;
}
}
//Android 4.4 PhoneWindowManager
@Override
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
// These types of windows can‘t receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
attrs.flags &= ~WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;
由上可知：
- Type為TYPE_TOAST：版本低於android4.4的，不能接受觸摸事件，無法操作；版本高於Android 7.1.1的無法添加懸浮窗
- Type為TYPE_PHONE：所有android版本都需要權限，版本低於android6.0的manifest中添加權限android.Manifest.permission.SYSTEM_ALERT_WINDOW即可，高於andorid6.0的需要判斷權限且手動添加。
- Type為TYPE_SYSTEM_ALERT：同TYPE_PHONE
所以系統級別的懸浮窗，android不同版本需要特別處理。
2.應用懸浮窗
對於應用懸浮窗來說，android版本對其影響不大。
- Type為TYPE_APPLICATION：只要Activity建立了，就可以添加。
- Type為TYPE_APPLICATION_ATTACHED_DIALOG：需要在Activity獲取焦點，並且用戶可操作時才可添加。
三、懸浮窗的實現
懸浮窗添加比較簡單,主要是由WindowManager接口的實現類WindowManagerImpl進行操作，WindowManager接口又繼承至ViewManager,其中主要方法為：
public void addView(View view, ViewGroup.LayoutParams params);//添加View到Window
public void updateViewLayout(View view, ViewGroup.LayoutParams params);//更新View在Window中的位置
public void removeView(View view);//刪除View- 1
- 2
- 3
主要實現代碼：
public class ContactWindowUtil {
private ContactView contactView;
private View dialogView;
private WindowManager windowManager;
private WindowManager.LayoutParams layoutParams;
private WindowManager.LayoutParams dialogParams;
private Context mContext;
private ContactWindowListener mListener;
private ValueAnimator valueAnimator;
private int direction;
private final int LEFT = 0;
private final int RIGHT = 1;
public interface ContactWindowListener {
void onDataCallBack(String str);
}
public void setDialogListener(ContactWindowListener listener) {
mListener = listener;
}
//私有化構造函數
public ContactWindowUtil(Context context) {
mContext = context;
windowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
// windowManager = (WindowManager) FloatWindowApp.getAppContext().getSystemService(Context.WINDOW_SERVICE);
}
public void showContactView() {
hideContactView();
contactView = new ContactView(mContext);
if (layoutParams == null) {
layoutParams = new WindowManager.LayoutParams();
layoutParams.width = contactView.width;
layoutParams.height = contactView.height;
layoutParams.x += ScreenSizeUtil.getScreenWidth();
layoutParams.y += ScreenSizeUtil.getScreenHeight() - ScreenSizeUtil.dp2px(150);
layoutParams.gravity = Gravity.TOP | Gravity.LEFT;
if (Build.VERSION.SDK_INT > 18 && Build.VERSION.SDK_INT < 23) {
layoutParams.type = WindowManager.LayoutParams.TYPE_TOAST;
} else {
layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION;
}
layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;
layoutParams.format = PixelFormat.RGBA_8888;
}
contactView.setOnTouchListener(touchListener);
contactView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
showContactDialog();
}
});
windowManager.addView(contactView, layoutParams);
}
/**
* 顯示聯系彈框
*/
private void showContactDialog() {
hideDialogView();
if (dialogParams == null) {
dialogParams = new WindowManager.LayoutParams();
dialogParams.width = WindowManager.LayoutParams.MATCH_PARENT;
dialogParams.height = WindowManager.LayoutParams.MATCH_PARENT;
dialogParams.gravity = Gravity.CENTER;
if (Build.VERSION.SDK_INT > 18 && Build.VERSION.SDK_INT < 25){
dialogParams.type = WindowManager.LayoutParams.TYPE_TOAST;
} else {
dialogParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_ATTACHED_DIALOG;
}
dialogParams.flags = WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
| WindowManager.LayoutParams.FLAG_FULLSCREEN;
dialogParams.format = PixelFormat.RGBA_8888;
}
LayoutInflater layoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
dialogView = layoutInflater.inflate(R.layout.window_contact, null);
TextView okTv = dialogView.findViewById(R.id.mOkTv);
TextView cancleTv = dialogView.findViewById(R.id.mCancleTv);
final TextView contentTv = dialogView.findViewById(R.id.mContentTv);
contentTv.setText(String.format("您確認撥打%s客服電話嗎", "4008-111-222"));
cancleTv.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
hideDialogView();
}
});
okTv.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
hideDialogView();
mListener.onDataCallBack("");
}
});
dialogView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
hideDialogView();
}
});
windowManager.addView(dialogView, dialogParams);
}
public void hideAllView() {
hideContactView();
hideDialogView();
}
public void hideContactView() {
if (contactView != null) {
windowManager.removeView(contactView);
contactView = null;
stopAnim();
}
}
public void hideDialogView() {
if (dialogView != null) {
windowManager.removeView(dialogView);
dialogView = null;
}
}
View.OnTouchListener touchListener = new View.OnTouchListener() {
float startX;
float startY;
float moveX;
float moveY;
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startX = event.getRawX();
startY = event.getRawY();
moveX = event.getRawX();
moveY = event.getRawY();
break;
case MotionEvent.ACTION_MOVE:
float x = event.getRawX() - moveX;
float y = event.getRawY() - moveY;
//計算偏移量，刷新視圖
layoutParams.x += x;
layoutParams.y += y;
windowManager.updateViewLayout(contactView, layoutParams);
moveX = event.getRawX();
moveY = event.getRawY();
break;
case MotionEvent.ACTION_UP:
//判斷松手時View的橫坐標是靠近屏幕哪一側，將View移動到依靠屏幕
float endX = event.getRawX();
float endY = event.getRawY();
if (endX < ScreenSizeUtil.getScreenWidth() / 2) {
direction = LEFT;
endX = 0;
} else {
direction = RIGHT;
endX = ScreenSizeUtil.getScreenWidth() - contactView.width;
}
if(moveX != startX){
starAnim((int) moveX, (int) endX,direction);
}
//如果初始落點與松手落點的坐標差值超過5個像素，則攔截該點擊事件
//否則繼續傳遞，將事件交給OnClickListener函數處理
if (Math.abs(startX - moveX) > 5) {
return true;
}
break;
}
return false;
}
};
private void starAnim(int startX, int endX,final int direction) {
if (valueAnimator != null) {
valueAnimator.cancel();
valueAnimator = null;
}
valueAnimator = ValueAnimator.ofInt(startX, endX);
valueAnimator.setDuration(500);
valueAnimator.setRepeatCount(0);
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
if(direction == LEFT){
layoutParams.x = (int) animation.getAnimatedValue()-contactView.width/2;
}else{
layoutParams.x = (int) animation.getAnimatedValue();
}
if (contactView != null) {
windowManager.updateViewLayout(contactView, layoutParams);
}
}
});
valueAnimator.setInterpolator(new LinearInterpolator());
valueAnimator.start();
}
private void stopAnim() {
if (valueAnimator != null) {
valueAnimator.cancel();
valueAnimator = null;
懸浮窗源碼:https://github.com/awenzeng/FloatWindowDemo
四、註意
1.應用懸浮窗WindowManager的獲取環境必須是Activity環境，系統懸浮窗可以Activity環境，也可以是全局的環境。如：
windowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
// windowManager = (WindowManager) FloatWindowApp.getAppContext().getSystemService(Context.WINDOW_SERVICE);- 1
- 2
2.應用級別懸浮窗也可以通過系統級別的方式實現，主要控制一下顯示與隱藏就好。但如果只在應用中展示懸浮窗，建議使用應用級別，那樣會省去許多不必要的麻煩。
3.系統級別Type為TYPE_PHONE、TYPE_SYSTEM_ALERT是權限判斷及設置代碼：
/**
* 請求用戶給予懸浮窗的權限
*/
public void askForPermission() {
if (!Settings.canDrawOverlays(this)) {
Toast.makeText(TestFloatWinActivity.this, "當前無權限，請授權！", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
Uri.parse("package:" + getPackageName()));
startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
} else {
startService(floatWinIntent);
}
} Android懸浮窗原理解析(Window)[源碼]