[移动开发]Android添加自定义系统广播

最近有一个需求，要求实现20秒无操作就跳转到一个界面，因为开发初期没有添加BaseActivity，所以再想在APP中实现事件监听就比较难修改，查阅资料发现可以在framework的ViewRootImpl类的内部类WindowInputEventReceiver的onInputEvent方法中添加广播实现，但是添加后发现会有Sending non-protected broadcast的报错，于是又查阅资料，将添加的广播在AndroidManifest.xml中注册为protected-broadcast:

<protected-broadcast android:name="android.intent.action.xxx" />

添加了之后，又发现非系统应用再点击任何按键时都会闪退，查看报错以及查阅资料发现，protected-broadcast是为了防止三方垃圾应用也发送这些广播，会进行权限检查，不通过时，会抛出一个异常，具体代码在ActivityManagerService中的checkBroadcastFromSystem方法中:

private void checkBroadcastFromSystem(Intent intent, ProcessRecord callerApp,
            String callerPackage, int callingUid, boolean isProtectedBroadcast, List receivers) {
        if ((intent.getFlags() & Intent.FLAG_RECEIVER_FROM_SHELL) != 0) {
            // Don't yell about broadcasts sent via shell
            return;
        }

        final String action = intent.getAction();
        if (isProtectedBroadcast
                || Intent.ACTION_CLOSE_SYSTEM_DIALOGS.equals(action)
                || Intent.ACTION_DISMISS_KEYBOARD_SHORTCUTS.equals(action)
                || Intent.ACTION_MEDIA_BUTTON.equals(action)
                || Intent.ACTION_MEDIA_SCANNER_SCAN_FILE.equals(action)
                || Intent.ACTION_SHOW_KEYBOARD_SHORTCUTS.equals(action)
                || Intent.ACTION_MASTER_CLEAR.equals(action)
                || Intent.ACTION_FACTORY_RESET.equals(action)
                || AppWidgetManager.ACTION_APPWIDGET_CONFIGURE.equals(action)
                || AppWidgetManager.ACTION_APPWIDGET_UPDATE.equals(action)
                || LocationManager.HIGH_POWER_REQUEST_CHANGE_ACTION.equals(action)
                || TelephonyIntents.ACTION_REQUEST_OMADM_CONFIGURATION_UPDATE.equals(action)
                || SuggestionSpan.ACTION_SUGGESTION_PICKED.equals(action)
                || AudioEffect.ACTION_OPEN_AUDIO_EFFECT_CONTROL_SESSION.equals(action)
                || AudioEffect.ACTION_CLOSE_AUDIO_EFFECT_CONTROL_SESSION.equals(action)) {
            // Broadcast is either protected, or it's a public action that
            // we've relaxed, so it's fine for system internals to send.
            return;
        }

        ******
        
        if (callerApp != null) {
            Log.wtf(TAG, "Sending non-protected broadcast " + action
                            + " from system " + callerApp.toShortString() + " pkg " + callerPackage,
                    new Throwable());
        } else {
            Log.wtf(TAG, "Sending non-protected broadcast " + action
                            + " from system uid " + UserHandle.formatUid(callingUid)
                            + " pkg " + callerPackage,
                    new Throwable());
        }
    }

所以问题就简单了，在上面的判断中加入自定义的系统广播即可，根据具体需求，看是否要添加到Intent类中作为常量，比如需求提供给第三方SDK时，可以添加一下。

综上，要添加一个自定义的系统广播，首先要在frameworks\base\core\res\AndroidManifest.xml中注册成protected-broadcast，然后需要在ActivityManagerService中添加判断；这样才能在framework中使用这个广播。