Android飞行模式示例

Question

I used this piece of code to turn on and off airplane mode of a Android 4.1.2 device:

boolean isEnabled = Settings.System.getInt(
                     getContentResolver(),
                     Settings.System.AIRPLANE_MODE_ON, 0) == 1;

             Settings.System.putInt(
                     getContentResolver(),
                     Settings.System.AIRPLANE_MODE_ON, isEnabled ? 0 : 1);

             Intent intent = new Intent(Intent.ACTION_AIRPLANE_MODE_CHANGED);
             intent.putExtra("state", !isEnabled);
             sendBroadcast(intent);

The code runs fine, but in order to fully understand why it works I have some questions.

1. Why this code doesn't work if I comment:

   Intent intent = new Intent(Intent.ACTION_AIRPLANE_MODE_CHANGED); intent.putExtra("state", !isEnabled); sendBroadcast(intent);

2. Do I have to always to broadcast an intent after I make any changes in the settings?

Could someone please explain it in more details?

Answer 1

Settings.System.putInt() actually changes the int value, but the system does not notifies it. It does not read this setting in a loop...

So, to make the system aware of that change, you send a broadcast that the system listen to, will then parse its content, notice the setting change and do stuff accordingly.

So you can't have this code to work without sending the broadcast, because that's what notifies the system about the change you just made. And yes you have to use that broadcast to notice it.