How to create an UI or a widget that sits on top of all applications in Android?

问题

Can I create an UI or a widget in Android that will sit on top of all applications? There are applications that have widgets like this. One example has a camera icon on top of all the applications that, when clicked, will capture the screen.

回答1:

If you want to just display something, you can display it on top of everything even the lockscreen.

If you want something to be clickable, you can display it on top of anything except the lockscreen.

Here's a sample, modify to your needs:

Create a service and do the following:

//These three are our main components.
WindowManager wm;
LinearLayout ll;
WindowManager.LayoutParams ll_lp;

//Just a sample layout parameters.
ll_lp = new WindowManager.LayoutParams();
ll_lp.format = PixelFormat.TRANSLUCENT;
ll_lp.height = WindowManager.LayoutParams.FILL_PARENT;
ll_lp.width = WindowManager.LayoutParams.FILL_PARENT;
ll_lp.gravity = Gravity.CLIP_HORIZONTAL | Gravity.TOP;

//This one is necessary.
ll_lp.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT;

//Play around with these two.
ll_lp.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
ll_lp.flags = ll_lp.flags | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;

//This is our main layout.
ll = new LinearLayout(this);
ll.setBackgroundColor(android.graphics.Color.argb(0, 0, 0, 0));
ll.setHapticFeedbackEnabled(true);

//And finally we add what we created to the screen.
wm.addView(ll, ll_lp);

回答2:

The following are more options for how the view is displayed.

This will make it an overlay on top of everything (including lock screen), but not clickable. WindowManager.LayoutParams. TYPE_SYSTEM_OVERLAY

This will make it clickable, but it won't be over the lock screen WindowManager.LayoutParams.TYPE_SYSTEM_ALERT

This will make it above everything (including lock screen) AND clickable. WindowManager.LayoutParams.TYPE_SYSTEM_ERROR

One thing to note about using "TYPE_SYSTEM_ERROR". If you wire-in a click event, anything it invokes will happen behind the lock screen.

来源：https://stackoverflow.com/questions/11498366/how-to-create-an-ui-or-a-widget-that-sits-on-top-of-all-applications-in-android