當我嘗試打開列表時應用崩潰

Question

我一直在編寫Bluettoth應用程序的程序，並完成了與配對設備的連接列表，沒有編譯器錯誤，但是當我嘗試在手機上打開它時，應用程序崩潰了，如果有人可以幫助我，我將不勝感激，下面是列表代碼，MainActivity代碼和logcat錯誤：

public class MainActivity extends AppCompatActivity {
    BluetoothAdapter BtAdapter = null;
    private final int REQUEST_ENABLE_BT = 1;
    private final int REQUEST_BT_CONECTION = 2;
    boolean conexao = false;
    public static String MAC = null;
    BluetoothDevice myDevice = null;
    BluetoothSocket mySocket = null;
    Button Frente, Tras, Esquerda, DIreita, Conectar;
    UUID myUUID = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb");

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

    BtAdapter = BluetoothAdapter.getDefaultAdapter();

    Frente = (Button)findViewById(R.id.Frente);
    Tras = (Button)findViewById(R.id.Tras);
    Esquerda = (Button)findViewById(R.id.Esquerda);
    DIreita = (Button)findViewById(R.id.Direita);
    Conectar = (Button)findViewById(R.id.Conectar);

    if(BtAdapter == null){
        Toast.makeText(getApplicationContext(), "Seu dispositivo nao possui bluetooth", Toast.LENGTH_LONG).show();
    } else if(!BtAdapter.isEnabled()){
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
    }

    Conectar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(conexao){

            } else {
                Intent openList = new Intent(MainActivity.this, DevicesList.class);
                startActivityForResult(openList, REQUEST_BT_CONECTION);

                //code not finhished
            }
        }
    });





}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    //super.onActivityResult(requestCode, resultCode, data);
    switch(requestCode){
        case REQUEST_ENABLE_BT:
            if(resultCode == Activity.RESULT_OK){

                Toast.makeText(getApplicationContext(), "O bluetooth foi ativado com sucesso", Toast.LENGTH_LONG).show();


            } else {

                Toast.makeText(getApplicationContext(), "O bluetooth nao foi ativado com sucesso, o app sera encerado", Toast.LENGTH_LONG).show();
                finish();

            }
        case REQUEST_BT_CONECTION:
            if (resultCode == Activity.RESULT_OK){

                MAC = data.getDataString();
                myDevice = BtAdapter.getRemoteDevice(MAC);
                try {
                mySocket = myDevice.createRfcommSocketToServiceRecord(myUUID);
                } catch (IOException erro) {

                }

            } else {

                Toast.makeText(getApplicationContext(), "Falha ao obter o endereco MAc do dispositivo", Toast.LENGTH_LONG);

            }
    }

}
}

這是deviceListActivity：

public class DevicesList extends ListActivity {
public BluetoothAdapter BtAdapter2 = null;
    public static String ENDERECO_MAC = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ArrayAdapter<String> ArrayBluetooth = new ArrayAdapter<String>(DevicesList.this, android.R.layout.simple_list_item_1);

        Set<BluetoothDevice> dispositivosPareados = BtAdapter2.getBondedDevices();

        if(dispositivosPareados.size() > 0){
            for(BluetoothDevice device : dispositivosPareados){
                String nomeBt = device.getName();
                String macBt = device.getAddress();
                ArrayBluetooth.add(nomeBt + "/n" + macBt);
            }
        }
        setListAdapter(ArrayBluetooth);
    }


    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        String infomacaoGeral = ((TextView) v).getText().toString();
         String enderecoMac = infomacaoGeral.substring(infomacaoGeral.length() - 17);

        Toast.makeText(getApplicationContext(), "Info:" + infomacaoGeral, Toast.LENGTH_LONG);

        Intent retornaMac = new Intent();
        retornaMac.putExtra(enderecoMac, ENDERECO_MAC);
        setResult(RESULT_OK);
        finish();

    }
}

這是錯誤堆棧跟蹤：

Process: com.example.lordz.bluetoothproject, PID: 25942 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lordz.bluetoothproject/com.example.lordz.bluetoothproject.DevicesList}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set android.bluetooth.BluetoothAdapter.getBondedDevices()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2955)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3030)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6938)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
      **Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set android.bluetooth.BluetoothAdapter.getBondedDevices()' on a null object reference**
        at com.example.lordz.bluetoothproject.DevicesList.onCreate(DevicesList.java:29)
        at android.app.Activity.performCreate(Activity.java:7183)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2908)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3030) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6938) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374) 

Answer 1

您的錯誤在於onCreate方法中，恰好在此行中：

Set<BluetoothDevice> dispositivosPareados = BtAdapter2.getBondedDevices();

BtAdapter2為null，因為您已在Activy類中將其聲明為null。

public BluetoothAdapter BtAdapter2 = null;

我認為您可能想先在onCreate中聲明BluetoothAdapter，然后使用它：

// inside onCreate
BtAdapter2 = BluetoothAdapter.getDefaultAdapter();
Set<BluetoothDevice> dispositivosPareados = BtAdapter2.getBondedDevices();

您的應用還必須檢查藍牙權限，並且可能會要求用戶提供藍牙權限。 有關更多參考，請訪問有關bt權限的stackoverflow問題 ，並訪問官方文檔中的藍牙概述 。