Question

我想通过BroadcastReceiver获得rssi值。当我在Android 4上实现以下代码时，效果很好（代码也只有BroadcastReceiver并注册了broadcastReceiver，并且没有该权限请求），但是在Android 6及更高版本中没有响应。我读到BroadcastReceiver已针对Android 6+进行了更改，它需要ACCESS_FINE_LOCATION和ACCESS_COARSE_LOCATION权限。我在android清单中添加了此权限，并在MainActivity中请求了权限，但是当我在装有Android 7的手机上运行代码并在蓝牙设备为在那附近，是抛出异常，当我单击按钮时附近没有东西时，它什么也没显示。这是我的代码：

public class MainActivity extends AppCompatActivity {
    private BluetoothAdapter BTAdapter = BluetoothAdapter.getDefaultAdapter();
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layout);
    Button button = (Button) findViewById(R.id.button);
    button.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v) {
        checkLocationPermission();
        proceedDiscovery();
        }
        });
        }



private final BroadcastReceiver receiver = new BroadcastReceiver(){
        @Override
        public void onReceive(Context context, Intent intent) {

            String action = intent.getAction();
            Toast.makeText(MainActivity.this,action, Toast.LENGTH_LONG).show();
            if(BluetoothDevice.ACTION_FOUND.equals(action)) {
                int rssi = intent.getShortExtra(BluetoothDevice.EXTRA_RSSI,Short.MIN_VALUE);
                String name = intent.getStringExtra(BluetoothDevice.EXTRA_NAME);
                TextView rssi_msg = (TextView) findViewById(R.id.textView);
                rssi_msg.setText(rssi_msg.getText() + name + " => " + rssi + "dBm"+"\n");
            }
        }
    };

protected void checkLocationPermission() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {
            {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, 0);
                int MY_PERMISSIONS_REQUEST = 200;
                int permissions=ContextCompat.checkSelfPermission (this,Manifest.permission.ACCESS_FINE_LOCATION);
                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST);
        }}
    }
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case 0: {
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    proceedDiscovery();
                } 
else{}
                break;
            }
        }}
    protected void proceedDiscovery() {
        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        filter.addAction(BluetoothDevice.ACTION_NAME_CHANGED);
        registerReceiver(receiver, filter);
        BTAdapter.startDiscovery();
    }}

并且我的android清单具有以下权限：

<uses-feature android:name="android.hardware.bluetooth" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

我从此链接获得权限帮助： correct procedure for BT device discovery on Marshmallow

logcat中的异常：

08-16 14:33:16.341 6630-6630/com.example.hanane.rssi E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.hanane.rssi, PID: 6630
    java.lang.RuntimeException: Error receiving broadcast Intent { act=android.bluetooth.device.action.FOUND flg=0x10 launchParam=MultiScreenLaunchParams { mDisplayId=0 mBaseDisplayId=0 mFlags=0 } bqHint=1 (has extras) } in com.example.hanane.rssi.MainActivity$2@a1e9394
        at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:1195)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6816)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1565)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1453)
     Caused by: android.content.res.Resources$NotFoundException: String resource ID #0xffffffd4
        at android.content.res.Resources.getText(Resources.java:1184)
        at android.widget.Toast.makeText(Toast.java:460)
        at com.example.hanane.rssi.MainActivity$2.onReceive(MainActivity.java:75)
        at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:1185)
        at android.os.Handler.handleCallback(Handler.java:751) 
        at android.os.Handler.dispatchMessage(Handler.java:95) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6816) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1565) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1453)

Answer 1

正如您所说的异常，问题在于调用

Toast.makeText(MainActivity.this,action, Toast.LENGTH_LONG).show();

如文档所述，Toast.makeText在传递R.string.<something>时要求字符串资源标识符（String）作为一个重载的第二个参数，或另一个action作为另一个重载，这导致Toast在找不到action值的标识符的情况下寻找资源。

如果要Toast的{{1}}值，则必须先将其转换为字符串。最简单的方法是将其用作action：

action + ""

通过BroadcastReceiver获得rssi的价值

1 个答案: