Android有關Home按鍵的TYPE_KEYGUARD作用的仿照及其流程說明

先看到PhoneWindowManager中public boolean interceptKeyTi(WindowState win, int code, int metaKeys, boolean down,
int repeatCount, int flags) 這個方法的實現，interceptKeyTi你可以暫時理解為WindowManagerService中處理驅動和上層按鍵實現的過濾器

1. if (code == KeyEvent.KEYCODE_HOME) {
3. // If a system window has focus, then it doesn't make sense
4. // right now to interact with applications.
5. WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;
6. if (attrs != null) {
7. final int type = attrs.type;
8. if (type == WindowManager.LayoutParams.TYPE_KEYGUARD
9. || type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {
10. // the "app" is keyguard, so give it the key
11. return false;
12. }
13. final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;
14. for (int i=0; i<typeCount; i++) {
15. if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i]) {
16. // don't do anything, but also don't pass it to the app
17. return true;
18. }
19. }
20. }

從上面的注釋可以看到注釋：// the "app" is keyguard, so give it the key ，就是說當在應用界面下的時候，按了HOME鍵而且當前應用的WindowManager.LayoutParams.type的值是WindowManager.LayoutParams.TYPE_KEYGUARD就讓直接返回；返回做什麼呢，我先告訴大家，這個interceptKeyTi方法被調用的地方的流程後續步驟就是根據這個interceptKeyTi的返回值來判斷，如果返回的是false就讓當前應用自己去做HOME鍵的業務處理通過類似下面的代碼

1. /* 按鍵按下 */
2. public boolean onKeyDown(int keyCode, KeyEvent event)
3. {
4. switch (keyCode)
5. {
6. case KeyEvent.KEYCODE_HOME:
7. DisplayToast("HOME鍵按下");
8. break;
10. }
11. return super.onKeyDown(keyCode, event);
13. }
15. /*按鍵彈起*/
16. public boolean onKeyUp(int keyCode, KeyEvent event)
17. {
18. switch (keyCode)
19. {
20. case KeyEvent.KEYCODE_HOME:
21. DisplayToast("HOME鍵彈起");
22. break;
24. }
26. return super.onKeyUp(keyCode, event);
27. }

這裡就產生了疑問：一、WindowManager.LayoutParams.type的值是在應用的哪裡初始化的，二、interceptKeyTi方法被調用的地方的流程後續步驟是怎麼調應用的HOME鍵的處理方式的，三、interceptKeyTi方法被調用的地方的流程後續步驟是怎麼獲取到WindowManager.LayoutParams.type初始化的值的；這三個疑問基本上就是按鍵的一個流程即怎麼通過底層驅動到Activity相應按鍵事件相應的。

下面我們來看第一個問題的解答：Activity中有兩個可覆蓋的方法,都可以做如下的初始化：

1. /**
2. * Called when the current {@link Window} of the activity gains or loses
3. * focus. This is the best indicator of whether this activity is visible
4. * to the user. The default implementation clears the key tracking
5. * state, so should always be called.
6. *
7. * <p>Note that this provides information about global focus state, which
8. * is managed independently of activity lifecycles. As such, while focus
9. * changes will generally have some relation to lifecycle changes (an
10. * activity that is stopped will not generally get window focus), you
11. * should not rely on any particular order between the callbacks here and
12. * those in the other lifecycle methods such as {@link #onResume}.
13. *
14. * <p>As a general rule, however, a resumed activity will have window
15. * focus... unless it has displayed other dialogs or popups that take
16. * input focus, in which case the activity itself will not have focus
17. * when the other windows have it. Likewise, the system may display
18. * system-level windows (such as the status bar notification panel or
19. * a system alert) which will temporarily take window input focus without
20. * pausing the foreground activity.
21. *
22. * @param hasFocus Whether the window of this activity has focus.
23. *
24. * @see #hasWindowFocus()
25. * @see #onResume
26. * @see View#onWindowFocusChanged(boolean)
27. */
28. public void onWindowFocusChanged(boolean hasFocus) {
29. WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
30. lp.type = WindowManager.LayoutParams.TYPE_KEYGUARD ;
31. this.getWindow().setAttributes(lp);
32. }
35. /** * Called when the main window associated with the activity has been
36. * attached to the window manager.
37. * See {@link View#onAttachedToWindow() View.onAttachedToWindow()}
38. * for more information.
39. * @see View#onAttachedToWindow
40. */
41. public void onAttachedToWindow() {
42. this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);
43. super.onAttachedToWindow();
44. }
47. onWindowFocusChanged(boolean) 當窗口包含的view獲取或失去焦點時觸發
48. onAttachedToWindow() 當view被附著到一個窗口時觸發