Android系统全屏时悬浮窗或者悬浮球向上移动的问题

当系统全屏时，很多悬浮窗会向上移动一小段距离，原因窗口布局是从状态栏之后开始的，全屏时没有状态栏了，所以会向上移动，给窗口加上
WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN 可以解决这个问题，这个 flag 经常和
WindowManager.LayoutParams.FLAG_LAYOUT_INSET_DECOR 一起使用。

mParams.flags = WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;

/** Window flag: place the window within the entire screen, ignoring * decorations around the border (such as the status bar). The * window must correctly position its contents to take the screen * decoration into account. This flag is normally set for you * by Window as described in {@link Window#setFlags}. */
public static final int FLAG_LAYOUT_IN_SCREEN = 0x00000100;

/** Window flag: a special option only for use in combination with * {@link #FLAG_LAYOUT_IN_SCREEN}. When requesting layout in the * screen your window may appear on top of or behind screen decorations * such as the status bar. By also including this flag, the window * manager will report the inset rectangle needed to ensure your * content is not covered by screen decorations. This flag is normally * set for you by Window as described in {@link Window#setFlags}.*/
public static final int FLAG_LAYOUT_INSET_DECOR = 0x00010000;