在Android上，我可以注册一个回调来告诉我蓝牙是打开还是关闭？

树木无处不在

我需要在我的应用程序内知道蓝牙是打开还是关闭。或者，例如从OS设置下拉菜单中打开或关闭了蓝牙。我以为可以在“活动”中执行此操作onResume()。但是事实证明，打开Android OS的设置“下拉菜单”（通过从屏幕顶部边缘用手指下拉来访问该菜单）时，活动不会暂停。

蓝牙可用或不可用时，我需要更新UI。

我可以注册一个回调（例如BroadcastReceiver）或任何其他回调以让系统在蓝牙可用性发生变化时告诉我吗？

马蒂亚·梅斯特里尼（Mattia Maestrini）

您可以使用意图过滤器注册接收器：

<receiver
        android:name="com.example.BluetoothReceiver"
        android:enabled="true">
    <intent-filter>
        <action android:name="android.bluetooth.adapter.action.STATE_CHANGED"/>
    </intent-filter>
</receiver>

这是BroadcastReceiver：

public class BluetoothReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();

        if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
            int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, -1);

            switch (state){
                case BluetoothAdapter.STATE_OFF:
                    //Indicates the local Bluetooth adapter is off.
                break;

                case BluetoothAdapter.STATE_TURNING_ON:
                    //Indicates the local Bluetooth adapter is turning on. However local clients should wait for STATE_ON before attempting to use the adapter.
                break;

                case BluetoothAdapter.STATE_ON:
                    //Indicates the local Bluetooth adapter is on, and ready for use.
                break;

                case BluetoothAdapter.STATE_TURNING_OFF:
                    //Indicates the local Bluetooth adapter is turning off. Local clients should immediately attempt graceful disconnection of any remote links.
                break;
            }
        }
    }
};

或者，如果您想直接在活动中添加：

public class ExampleActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_example);
    }

    @Override
    protected void onResume() {
        super.onResume();
        registerReceiver(mReceiver, new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED));
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterReceiver(mReceiver);
    }

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();

            if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
                int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, -1);

                switch (state) {
                    case BluetoothAdapter.STATE_OFF:
                        //Indicates the local Bluetooth adapter is off.
                        break;

                    case BluetoothAdapter.STATE_TURNING_ON:
                        //Indicates the local Bluetooth adapter is turning on. However local clients should wait for STATE_ON before attempting to use the adapter.
                        break;

                    case BluetoothAdapter.STATE_ON:
                        //Indicates the local Bluetooth adapter is on, and ready for use.
                        break;

                    case BluetoothAdapter.STATE_TURNING_OFF:
                        //Indicates the local Bluetooth adapter is turning off. Local clients should immediately attempt graceful disconnection of any remote links.
                        break;
                }
            }
        }
    };
}

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