Android有关Home按键的TYPE_KEYGUARD作用

先看到PhoneWindowManager中public boolean interceptKeyTi(WindowState win, int code, int metaKeys, boolean down, 
            int repeatCount, int flags) 这个方法的实现，interceptKeyTi你可以暂时理解为WindowManagerService中处理驱动和上层按键实现的过滤器

if (code == KeyEvent.KEYCODE_HOME) {

    // If a system window has focus, then it doesn't make sense
    // right now to interact with applications.
    WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;
    if (attrs != null) {
        final int type = attrs.type;
        if (type == WindowManager.LayoutParams.TYPE_KEYGUARD
                || type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {
            // the "app" is keyguard, so give it the key
            return false;
        }
        final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;
        for (int i=0; i<typeCount; i++) {
            if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i]) {
                // don't do anything, but also don't pass it to the app
                return true;
            }
        }
    }

从上面的注释可以看到注释：// the "app" is keyguard, so give it the key ，就是说当在应用界面下的时候，按了HOME键而且当前应用的WindowManager.LayoutParams.type的值是WindowManager.LayoutParams.TYPE_KEYGUARD就让直接返回；返回做什么呢，我先告诉大家，这个interceptKeyTi方法被调用的地方的流程后续步骤就是根据这个interceptKeyTi的返回值来判断，如果返回的是false就让当前应用自己去做HOME键的业务处理通过类似下面的代码

/* 按键按下 */
  public boolean onKeyDown(int keyCode, KeyEvent event)
  {
      switch (keyCode)
      {
          case KeyEvent.KEYCODE_HOME:
              DisplayToast("HOME键按下");
              break;

      }
      return super.onKeyDown(keyCode, event);

  }

  /*按键弹起*/
  public boolean onKeyUp(int keyCode, KeyEvent event)
  {
      switch (keyCode)
      {
          case KeyEvent.KEYCODE_HOME:
              DisplayToast("HOME键弹起");
              break;

      }

      return super.onKeyUp(keyCode, event);
  }

这里就产生了疑问：一、WindowManager.LayoutParams.type的值是在应用的哪里初始化的，二、interceptKeyTi方法被调用的地方的流程后续步骤是怎么调应用的HOME键的处理方式的，三、interceptKeyTi方法被调用的地方的流程后续步骤是怎么获取到WindowManager.LayoutParams.type初始化的值的；这三个疑问基本上就是按键的一个流程即怎么通过底层驱动到Activity相应按键事件相应的。

下面我们来看第一个问题的解答：Activity中有两个可覆盖的方法,都可以做如下的初始化：

    /**
     * Called when the current {@link Window} of the activity gains or loses
     * focus.  This is the best indicator of whether this activity is visible
     * to the user.  The default implementation clears the key tracking
     * state, so should always be called.
     *
     * <p>Note that this provides information about global focus state, which
     * is managed independently of activity lifecycles.  As such, while focus
     * changes will generally have some relation to lifecycle changes (an
     * activity that is stopped will not generally get window focus), you
     * should not rely on any particular order between the callbacks here and
     * those in the other lifecycle methods such as {@link #onResume}.
     *
     * <p>As a general rule, however, a resumed activity will have window
     * focus...  unless it has displayed other dialogs or popups that take
     * input focus, in which case the activity itself will not have focus
     * when the other windows have it.  Likewise, the system may display
     * system-level windows (such as the status bar notification panel or
     * a system alert) which will temporarily take window input focus without
     * pausing the foreground activity.
     *
     * @param hasFocus Whether the window of this activity has focus.
     *
     * @see #hasWindowFocus()
     * @see #onResume
     * @see View#onWindowFocusChanged(boolean)
     */
    public void onWindowFocusChanged(boolean hasFocus) {
        WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
        lp.type = WindowManager.LayoutParams.TYPE_KEYGUARD ;
        this.getWindow().setAttributes(lp);
    }


    /** * Called when the main window associated with the activity has been
        * attached     to the window manager.
       * See {@link View#onAttachedToWindow() View.onAttachedToWindow()}
       * for more information.
      * @see View#onAttachedToWindow
     */
    public void onAttachedToWindow() {
         this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);
       super.onAttachedToWindow();
   }


onWindowFocusChanged(boolean) 当窗口包含的view获取或失去焦点时触发
onAttachedToWindow() 当view被附着到一个窗口时触发
LayoutParams的构造方式有很多种可以顺带学习下,同时最好学习下它的参数，项目中用到就知道它的重要性了： 
public LayoutParams() {
    super(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    type = TYPE_APPLICATION;
    format = PixelFormat.OPAQUE;
}

public LayoutParams(int _type) {
    super(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    type = _type;
    format = PixelFormat.OPAQUE;
}

public LayoutParams(int _type, int _flags) {
    super(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    type = _type;
    flags = _flags;
    format = PixelFormat.OPAQUE;
}

public LayoutParams(int _type, int _flags, int _format) {
    super(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    type = _type;
    flags = _flags;
    format = _format;
}

public LayoutParams(int w, int h, int _type, int _flags, int _format) {
    super(w, h);
    type = _type;
    flags = _flags;
    format = _format;
}

public LayoutParams(int w, int h, int xpos, int ypos, int _type,
        int _flags, int _format) {
    super(w, h);
    x = xpos;
    y = ypos;
    type = _type;
    flags = _flags;
    format = _format;
}
到这一步为至即为网上很多转的都一样的帖子即屏蔽Home键写一些自己的业务逻辑