java - button.performclick() java.lang.NullPointerException

Question

我正在尝试修改应用程序以添加其他功能。我有一个看起来像这样的功能

public class MainActivity extends Activity implements RadioGroup.OnCheckedChangeListener {
    private static final int REQUEST_SELECT_DEVICE = 1;
    private static final int REQUEST_ENABLE_BT = 2;
    public static final String TAG = "nRFUART";
    private static final String TAG1 = "smsTAG";
    private static final int UART_PROFILE_CONNECTED = 20;
    private static final int UART_PROFILE_DISCONNECTED = 21;
    public static String content = null;
    private int mState = UART_PROFILE_DISCONNECTED;
    private UartService mService = null;
    private BluetoothDevice mDevice = null;
    private BluetoothAdapter mBtAdapter = null;
    private ListView messageListView;
    private ArrayAdapter<String> listAdapter;
    public Button btnConnectDisconnect,btnSend;
    private EditText edtMessage;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mBtAdapter = BluetoothAdapter.getDefaultAdapter();
        if (mBtAdapter == null) {
            Toast.makeText(this, "Bluetooth is not available", Toast.LENGTH_LONG).show();
        }else{

            btnConnectDisconnect=(Button) findViewById(R.id.btn_select);
            btnSend=(Button) findViewById(R.id.sendButton);
            edtMessage = (EditText) findViewById(R.id.sendText);
            mBtAdapter = BluetoothAdapter.getDefaultAdapter();
            messageListView = (ListView) findViewById(R.id.listMessage);
            listAdapter = new ArrayAdapter<String>(this, R.layout.message_detail);
            messageListView.setAdapter(listAdapter);
            messageListView.setDivider(null);
            //Call receiveBroadCast like this
            receiveBroadCast(getIntent().getStringExtra("message"));
            service_init();
        }

    ...

        // Handle Send button
        btnSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText editText = (EditText) findViewById(R.id.sendText);
//              String message = editText.getText().toString();
                String message = content;
                byte[] value;
                try {
                    //send data to service
                    value = message.getBytes("UTF-8");
                    mService.writeRXCharacteristic(value);
                    //Update the log with time stamp
                    String currentDateTimeString = DateFormat.getTimeInstance().format(new Date());
                    listAdapter.add("["+currentDateTimeString+"] TX: "+ message);
                    messageListView.smoothScrollToPosition(listAdapter.getCount() - 1);
                    edtMessage.setText("");
                    Log.i(TAG1, "success, value: " + value + " message: " + message);
                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Log.i(TAG1, "fail" + e.toString());
                }
            }
        });

        ...

    }

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    public void receiveBroadCast(String text) {
        btnSend=(Button) findViewById(R.id.sendButton);
        Log.i(TAG1, "test " + text);
        try {
            Log.i(TAG1, "success " + text);
            content = text;
            btnSend.performClick();
        } catch (Exception e) {
            Log.i(TAG1, "fail " + e.toString());
        }
    }
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

但是当我运行代码时，我得到了错误

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference

这是包含我的按钮的 main.xml 文件

        <Button
            android:id="@+id/sendButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_alignParentBottom="true"
            android:layout_marginRight="0dp"
            android:layout_marginBottom="0dp"
            android:enabled="false"
            android:text="Send" />

知道是什么导致了这个错误吗？

每次我向接收广播提供字符串时，我都试图让我的接收广播自动单击发送按钮。

这是我用来调用 receiveBroadcast 的 SMSReceiver 类：

public class SmsReceiver extends BroadcastReceiver {
    private static final String TAG = "MyBroadcastReceiver";
    @Override
    public void onReceive(Context context, Intent intent) {
        if(intent.getAction().equals("android.provider.Telephony.SMS_RECEIVED")) {
            Bundle bundle = intent.getExtras();
            SmsMessage[] msgs = null;
            if (bundle != null){
                try{
                    Object[] pdus = (Object[]) bundle.get("pdus");
                    msgs = new SmsMessage[pdus.length];
                    for(int i=0; i<msgs.length; i++){
                        msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);
                        String msgBody = msgs[i].getMessageBody();
                        Log.i(TAG, " success " + msgBody);
                        MainActivity Text = new MainActivity();
                        Text.receiveBroadCast(msgBody);
                        Intent intentsms = new Intent(context, MainActivity.class);
                        intentsms.putExtra("message", msgBody);
                        context.startActivity(intentsms);
                    }
                } catch(Exception e) {
                    Log.i(TAG, e.toString());
                }
            }
        }
    }
}

标签： javaandroidmobile

Answer 1

让那件事为你工作。您必须将 LocalBroadCastManager 发送到 MainActivity，然后您必须在那里获取该数据才能执行您的操作。

检查以下实现：

public class MainActivity extends Activity implements RadioGroup.OnCheckedChangeListener {
    private static final int REQUEST_SELECT_DEVICE = 1;
    private static final int REQUEST_ENABLE_BT = 2;
    public static final String TAG = "nRFUART";
    private static final String TAG1 = "smsTAG";
    private static final int UART_PROFILE_CONNECTED = 20;
    private static final int UART_PROFILE_DISCONNECTED = 21;
    public static String content = null;
    private int mState = UART_PROFILE_DISCONNECTED;
    private UartService mService = null;
    private BluetoothDevice mDevice = null;
    private BluetoothAdapter mBtAdapter = null;
    private ListView messageListView;
    private ArrayAdapter<String> listAdapter;
    public Button btnConnectDisconnect,btnSend;
    private EditText edtMessage;


    private BroadcastReceiver myMessageRec = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            // Get extra data included in the Intent
            String message = intent.getStringExtra("message");
            Log.d("receiver", "Got message: " + message);
            receiveBroadCast(message);
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        LocalBroadcastManager.getInstance(MainActivity.this).registerReceiver(myMessageRec,
                new IntentFilter("myMessage"));
        btnConnectDisconnect = (Button) findViewById(R.id.btn_select);
        btnSend = (Button) findViewById(R.id.sendButton);
        edtMessage = (EditText) findViewById(R.id.sendText);
        mBtAdapter = BluetoothAdapter.getDefaultAdapter();
        messageListView = (ListView) findViewById(R.id.listMessage);
        listAdapter = new ArrayAdapter<String>(this, R.layout.message_detail);
        messageListView.setAdapter(listAdapter);
        messageListView.setDivider(null);
        service_init();

        // Handle Send button
        btnSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText editText = (EditText) findViewById(R.id.sendText);
//              String message = editText.getText().toString();
                String message = content;
                byte[] value;
                try {
                    //send data to service
                    value = message.getBytes("UTF-8");
                    mService.writeRXCharacteristic(value);
                    //Update the log with time stamp
                    String currentDateTimeString = DateFormat.getTimeInstance().format(new Date());
                    listAdapter.add("[" + currentDateTimeString + "] TX: " + message);
                    messageListView.smoothScrollToPosition(listAdapter.getCount() - 1);
                    edtMessage.setText("");
                    Log.i(TAG1, "success, value: " + value + " message: " + message);
                } catch (UnsupportedEncodingException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Log.i(TAG1, "fail" + e.toString());
                }
            }
        });

    }

    public void receiveBroadCast(String text) {
        Log.i(TAG1, "test " + text);
        try {
            Log.i(TAG1, "success " + text);
            content = text;
            btnSend.performClick();
        } catch (Exception e) {
            Log.i(TAG1, "fail " + e.toString());
        }
    }

    @Override
    protected void onDestroy() {
        // Unregister since the activity is about to be closed.
        LocalBroadcastManager.getInstance(MainActivity.this).unregisterReceiver(myMessageRec);
        super.onDestroy();
    }


}

SmsReceiver 将如下所示：

public class SmsReceiver extends BroadcastReceiver {
        private static final String TAG = "MyBroadcastReceiver";
        @Override
        public void onReceive(Context context, Intent intent) {
            if(intent.getAction().equals("android.provider.Telephony.SMS_RECEIVED")) {
                Bundle bundle = intent.getExtras();
                SmsMessage[] msgs = null;
                String str = "";
                if (bundle != null) {
                    Object[] pdus = (Object[]) bundle.get("pdus");
                    msgs = new SmsMessage[pdus.length];
                    for (int i=0; i<msgs.length; i++){
                        msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);
                        str += "SMS from " + msgs[i].getOriginatingAddress();
                        str += " :";
                        str += msgs[i].getMessageBody().toString();
                        str += "\n";
                    }
                }
                Intent intentsms = new Intent("myMessage");
                intentsms.putExtra("message", str);
                LocalBroadcastManager.getInstance(context).sendBroadcast(intentsms);
            }
        }
    }