怎么监听蓝牙的开启状态？

if (action.equals(BluetoothAdapter.ACTION_STATE_CHANGED)) {
    int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE,
            BluetoothAdapter.ERROR);
    switch (state) {
        case BluetoothAdapter.STATE_OFF:
            Log.d("aaa", "STATE_OFF 手机蓝牙关闭");
            break;
        case BluetoothAdapter.STATE_TURNING_OFF:
            Log.d("aaa", "STATE_TURNING_OFF 手机蓝牙正在关闭");
            break;
        case BluetoothAdapter.STATE_ON:
            Log.d("aaa", "STATE_ON 手机蓝牙开启");
            break;
        case BluetoothAdapter.STATE_TURNING_ON:
            Log.d("aaa", "STATE_TURNING_ON 手机蓝牙正在开启");
            break;
    }
}
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