andriod 防止截屏

 WindowManager.LayoutParams 是 WindowManager 接口的嵌套类；它继承于 ViewGroup.LayoutParams； 它用于向WindowManager描述Window的管理策略。

主要成员常量

Window flag系列

该系列主要用于对Window的flag进行设置。设置Window的flag,可以直接对Window的getAttributes()得到其 WindowManager.LayoutParams对象,然后直接对它flag变量操作。也可以Window的addFlags(int flags)方法，setFlags(int flags, int mask)方法，clearFlags(int flags)方法进行操作。

比如设置全屏 ：

 Window window = getWindow(); 

 WindowManager.LayoutParams winParams = win.getAttributes();

  winParams.flags=winParams.flags|WindowManager.LayoutParams.FLAG_FULLSCREEN ；

 或

 window.addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

 或

 window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); 

 取消全屏

 Window window = getWindow(); 

 winParams.flags=winParams.flags&~WindowManager.LayoutParams.FLAG_FULLSCREEN;

 或

  window.clearFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

 或

window.setFlags(0, WindowManager.LayoutParams.FLAG_FULLSCREEN);

所有Window flag如下：

int	FLAGS_CHANGED	用于表示flags发生了变化，关于此的详细内容请看后文。
int	FLAG_ALLOW_LOCK_WHILE_SCREEN_ON	Window flag: as long as this window is visible to the user, allow the lock screen to activate while the screen is on. 当该window对用户可见的时候，允许锁屏。
int	FLAG_ALT_FOCUSABLE_IM	Window flag: invert the state of FLAG_NOT_FOCUSABLE with respect to how this window interacts with the current method.
int	FLAG_BLUR_BEHIND	Window flag: blur everything behind this window. 让该window后所有东西都模糊（blur）
int	FLAG_DIM_BEHIND	Window flag: everything behind this window will be dimmed. 让该window后所有的东西都成暗淡（dim）
int	FLAG_DISMISS_KEYGUARD	Window flag: when set the window will cause the keyguard to be dismissed, only if it is not a secure lock keyguard.
int	FLAG_DITHER	Window flag: turn on dithering when compositing this window to the screen. 开启抖动（dithering）
int	FLAG_FORCE_NOT_FULLSCREEN	Window flag: Override {@link #FLAG_FULLSCREEN and force the screen decorations (such as status bar) to be shown. 恢复window非全屏显示
int	FLAG_FULLSCREEN	Window flag: Hide all screen decorations (e.g. 让window进行全屏显示
int	FLAG_HARDWARE_ACCELERATED	Indicates whether this window should be hardware accelerated. 对该window进行硬件加速. 该flag必须在设置你的Activity或Dialog的Content View之前进行设置， 而且如果你在mainfest文件中用android:hardwareAccelerated开启了该属性的话，那么你在程序中就不能再改变它。mainfest文件中android:hardwareAccelerated属性默认是开启的("true")。
int	FLAG_IGNORE_CHEEK_PRESSES	Window flag: intended for windows that will often be used when the user is holding the screen against their face, it will aggressively filter the event stream to prevent unintended presses in this situation that may not be desired for a particular window, when such an event stream is detected, the application will receive a CANCEL motion event to indicate this so applications can handle this accordingly by taking no action on the event until the finger is released.
int	FLAG_KEEP_SCREEN_ON	Window flag: as long as this window is visible to the user, keep the device's screen turned on and bright. 当该window对用户可见时，让设备屏幕处于高亮（bright）状态。
int	FLAG_LAYOUT_INSET_DECOR	Window flag: a special option only for use in combination with FLAG_LAYOUT_IN_SCREEN.
int	FLAG_LAYOUT_IN_SCREEN	Window flag: place the window within the entire screen, ignoring decorations around the border (a.k.a. 让window占满整个手机屏幕，不留任何边界（border）
int	FLAG_LAYOUT_NO_LIMITS	Window flag: allow window to extend outside of the screen. window大小不再不受手机屏幕大小限制，即window可能超出屏幕之外，这时部分内容在屏幕之外。
int	FLAG_NOT_FOCUSABLE	Window flag: this window won't ever get key input focus, so the user can not send key or other button events to it. 让window不能获得焦点，这样用户快就不能向该window发送按键事件及按钮事件
int	FLAG_NOT_TOUCHABLE	Window flag: this window can never receive touch events. 让该window不接受触摸屏事件
int	FLAG_NOT_TOUCH_MODAL	Window flag: Even when this window is focusable (its {@link #FLAG_NOT_FOCUSABLE is not set), allow any pointer events outside of the window to be sent to the windows behind it. 即使在该window在可获得焦点情况下，仍然把该window之外的任何event发送到该window之后的其他window.
int	FLAG_SCALED	Window flag: a special mode where the layout parameters are used to perform scaling of the surface when it is composited to the screen.
int	FLAG_SECURE	Window flag: don't allow screen shots while this window is displayed. 当该window在进行显示的时候，不允许截屏。
int	FLAG_SHOW_WALLPAPER	Window flag: ask that the system wallpaper be shown behind your window. 在该window后显示系统的墙纸（wallpaper）
int	FLAG_SHOW_WHEN_LOCKED	Window flag: special flag to let windows be shown when the screen is locked. 当锁屏的时候，显示该window.
int	FLAG_SPLIT_TOUCH	Window flag: when set the window will accept for touch events outside of its bounds to be sent to other windows that also support split touch. When this flag is not set, the first pointer that goes down determines the window to which all subsequent touches go until all pointers go up. When this flag is set, each pointer (not necessarily the first) that goes down determines the window to which all subsequent touches of that pointer will go until that pointer goes up thereby enabling touches with multiple pointers to be split across multiple windows 当该window在可以接受触摸屏情况下，让因在该window之外，而发送到后面的window的触摸屏可以支持split touch.
int	FLAG_TOUCHABLE_WHEN_WAKING	Window flag: When set, if the device is asleep when the touch screen is pressed, you will receive this first touch event. 当手机处于睡眠状态时，如果屏幕被按下，那么该window将第一个收到到事件
int	FLAG_TURN_SCREEN_ON	Window flag: when set as a window is being added or made visible, once the window has been shown then the system will poke the power manager's user activity (as if the user had woken up the device) to turn the screen on. 当然window被显示的时候，系统将把它当做一个用户活动事件，以点亮手机屏幕。
int	FLAG_WATCH_OUTSIDE_TOUCH	Window flag: if you have set FLAG_NOT_TOUCH_MODAL, you can set this flag to receive a single special MotionEvent with the action MotionEvent.ACTION_OUTSIDE  for touches that occur outside of your window. 如果你设置了该flag,那么在你FLAG_NOT_TOUNCH_MODAL的情况下，即使触摸屏事件发送在该window之外，其事件被发送到了后面的window,那么该window仍然将以MotionEvent.ACTION_OUTSIDE形式收到该触摸屏事件