Question

大家早上好，

我遇到过AlertDialog的一些问题。我有一个EditText组件，我想在MainActivity的变量中输入文本。

这是我的代码：

private void showDialog() {
    final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
    final EditText input = new EditText(MainActivity.this);

    builder.setTitle(R.string.title);
    builder.setMessage(R.string.enter_comment);
    builder.setView(input);

    builder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
// name is the variable I want to change. It has been declared as String name; at the beginning of my MainActivity class.
            name = input.getText().toString();
            showToast(name);
        }
    });

    builder.setNegativeButton(R.string.annuler, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
        }
    });

    this.runOnUiThread(new Runnable() {
        public void run() {
            builder.show();
        }
    });
// This line makes the app crash. It doesn't print "Null String" as it should.
    //showToast(name);
}

private void showToast(String str) {
    if (str != null) {
        Toast.makeText(MainActivity.this, str, Toast.LENGTH_SHORT).show();
    }else{
        Toast.makeText(MainActivity.this, "Null String", Toast.LENGTH_SHORT).show();
    }

}

我希望你能帮助我。提前谢谢！

编辑 - 添加完整代码（导入除了＆gt;太多）

package com.example.ghost.boxmonitor;



public class MainActivity extends Activity {
    public final String ACTION_USB_PERMISSION = "com.ghost.boxmonitor.USB_PERMISSION";
    Button startButton, clearButton, stopButton;
    TextView textView;
    UsbManager usbManager;
    UsbDevice device;
    UsbSerialDevice serialPort;
    UsbDeviceConnection connection;
    LinkedList<Box> list;
    String text,name;

UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() { //Defining a Callback which triggers whenever data is read.
    @Override
    public void onReceivedData(byte[] arg0) {
        String data = null;
        try {
            data = new String(arg0, "UTF-8");
            data.concat("/n");
            tvAppend(textView, data);
            buildString(data);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }


    }
};
private final BroadcastReceiver broadcastReceiver = new BroadcastReceiver() { //Broadcast Receiver to automatically start and stop the Serial connection.
    @Override
    public void onReceive(Context context, Intent intent) {
        if (intent.getAction().equals(ACTION_USB_PERMISSION)) {
            boolean granted = intent.getExtras().getBoolean(UsbManager.EXTRA_PERMISSION_GRANTED);
            if (granted) {
                connection = usbManager.openDevice(device);
                serialPort = UsbSerialDevice.createUsbSerialDevice(device, connection);
                if (serialPort != null) {
                    if (serialPort.open()) { //Set Serial Connection Parameters.
                        setUiEnabled(true);
                        serialPort.setBaudRate(9600);
                        serialPort.setDataBits(UsbSerialInterface.DATA_BITS_8);
                        serialPort.setStopBits(UsbSerialInterface.STOP_BITS_1);
                        serialPort.setParity(UsbSerialInterface.PARITY_NONE);
                        serialPort.setFlowControl(UsbSerialInterface.FLOW_CONTROL_OFF);
                        serialPort.read(mCallback);
                        tvAppend(textView,"Serial Connection Opened!\n");

                    } else {
                        tvAppend(textView,"Port not opened\n");
                        Log.d("SERIAL", "PORT NOT OPEN");
                    }
                } else {
                    tvAppend(textView,"Port null\n");
                    Log.d("SERIAL", "PORT IS NULL");
                }
            } else {
                tvAppend(textView,"Perm not granted\n");
                Log.d("SERIAL", "PERM NOT GRANTED");
            }
        } else if (intent.getAction().equals(UsbManager.ACTION_USB_DEVICE_ATTACHED)) {
            onClickStart(startButton);
        } else if (intent.getAction().equals(UsbManager.ACTION_USB_DEVICE_DETACHED)) {
            onClickStop(stopButton);
        }
    }

};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    usbManager = (UsbManager) getSystemService(this.USB_SERVICE);
    startButton = (Button) findViewById(R.id.buttonStart);
    clearButton = (Button) findViewById(R.id.buttonClear);
    stopButton = (Button) findViewById(R.id.buttonStop);
    textView = (TextView) findViewById(R.id.textView);
    setUiEnabled(false);
    IntentFilter filter = new IntentFilter();
    filter.addAction(ACTION_USB_PERMISSION);
    filter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
    filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
    registerReceiver(broadcastReceiver, filter);
    list = new LinkedList<Box>();

}

public void setUiEnabled(boolean bool) {
    startButton.setEnabled(!bool);
    stopButton.setEnabled(bool);
    textView.setEnabled(bool);

}

public void onClickStart(View view) {

    HashMap<String, UsbDevice> usbDevices = usbManager.getDeviceList();
    if (!usbDevices.isEmpty()) {
        boolean keep = true;
        for (Map.Entry<String, UsbDevice> entry : usbDevices.entrySet()) {
            device = entry.getValue();
            int deviceVID = device.getVendorId();
            tvAppend(textView, "Device VID : "+Integer.toString(deviceVID)+"\n");
            if (deviceVID == 10755 || deviceVID == 9025)//Arduino Vendor ID
            {
                PendingIntent pi = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
                tvAppend(textView,"Arduino detected. Waiting for user authorization...\n");
                usbManager.requestPermission(device, pi);
                keep = false;
            } else {
                connection = null;
                device = null;
                tvAppend(textView,"This device is not an Arduino.\n");
            }

            if (!keep)
                break;
        }
    }
    else{
        tvAppend(textView,"No USB device detected.\n");
    }


}

public void onClickStop(View view) {
    setUiEnabled(false);
    serialPort.close();
    tvAppend(textView, "\nUSB device unplugged.\nSerial Connection Closed !\n");

}

public void onClickClear(View view) {
    textView.setText(" ");
    showDialog();
}

private void tvAppend(TextView tv, CharSequence text) {
    final TextView ftv = tv;
    final CharSequence ftext = text;

    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            ftv.append(ftext);
        }
    });
}

public void interpreter(String text){
    String table[] = text.split("&");
    String def = Integer.toString(list.size() + 1);
    if (table.length == 2) {
        if (list.isEmpty()) {
            //showDialog();
            Box b = new Box(table[0], table[1], def);
            list.add(b);
            //tvAppend(textView2, b.execute());
        } else {
            boolean isInList = false;
            for (Box b : list) {
                if (b.getAddr().compareTo(table[0]) == 0) {
                    isInList = true;
                    b.setState(table[1]);
                    //tvAppend(textView2, b.execute());
                }
            }
            if (!isInList) {
                //showDialog();
                Box b = new Box(table[0], table[1], def);
                list.add(b);
                //tvAppend(textView2, b.execute());
            }
        }
    }
}

public void buildString(String data){
    int len = data.length();
    char c;
    for (int i = 0; i<len; i++){
        c = data.charAt(i);
        switch (c){
            case '#':
                text = "";
                break;
            case '!':
                interpreter(text);
                break;
            default:
                text+=c;
                break;
        }
    }
}

private void showDialog() {
        final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        final EditText input = new EditText(MainActivity.this);

        builder.setTitle("Title");
        builder.setMessage("Message");
        builder.setView(input);

        builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                name = input.getText().toString();
                Log.d("MyTag", "name in onClick()" + name);
                showToast(name);
            }
        });

        builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        builder.show();
        showToast(name);
    }


private void showToast(String str) {
    if (str != null) {
        Toast.makeText(MainActivity.this, str, Toast.LENGTH_SHORT).show();
    }else{
        Toast.makeText(MainActivity.this, "Null String", Toast.LENGTH_SHORT).show();
    }

}

}

因此，每次我在串行线上接收数据时，我都会构建一个字符串，如果字符串完整，我会调用解释器。如果字符串描述了一个新Box，我调用showDialog方法让用户给它一个名字。

编辑编辑 - 解决方案

请参阅下面的答案以及相关评论。据我所知，你不能在UiThread之外的其他线程中更改UI（现在看来很明显，但是......）。

Answer 1

老实说，我也没有得到你的问题。

代码name = input.getText().toString();中的这一行会对name变量进行分配用日志检查 - 放

name = input.getText().toString();
Log.d("MyTag", "name in onClick()" + name);

然后在控制台中我看到：

所以它正在工作。解除dialog后，您可以使用name变量。
或者请详细说明。

<强> PS。一个提示。如果您在showDialog()中使用Activity方法，则无需使用runOnUiThread技巧。只需致电builder.show();即可。

好的，这里是Activity 的完整代码，一切正常，包括showDialog()方法结尾的Toast。

public class MainActivity extends AppCompatActivity {
    final String ACTION = "myActionForBroadcast";
    String name;

    private final BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.d("MyTag", "onReceive: context" + context.getPackageCodePath());
            showDialog();
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        IntentFilter filter = new IntentFilter();
        filter.addAction(ACTION);
        registerReceiver(broadcastReceiver, filter);

        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                Log.d("MyTag", "Handler run: before send broadcast");
                sendBroadcast(new Intent(ACTION));
            }
        }, 5_000);
    }

    private void showDialog() {
        final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
        final EditText input = new EditText(MainActivity.this);

        builder.setTitle("Title");
        builder.setMessage("Message");
        builder.setView(input);

        builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Log.d("MyTag", "showDialog onClick: name before assign " + name);
                name = input.getText().toString();
                Log.d("MyTag", "showDialog onClick: name after assign " + name);
                showToast(name);
            }
        });

        builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        Log.d("MyTag", "showDialog: before showing dialog");
        builder.show();
        Log.d("MyTag", "showDialog: before showing toast");
        showToast(name);
    }

    private void showToast(String str) {
        if (str != null) {
            Toast.makeText(MainActivity.this, str, Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(MainActivity.this, "Null String", Toast.LENGTH_SHORT).show();
        }

    }
}

我改变了Activity的代码。这是做了什么：
1）我宣布receiver有一些自定义动作;
2）我在开始后5秒钟模仿onReceive();
3）在onReceive()我刚刚显示了对话框：
4）将日志放在事件上。

一切正常，请在控制台中查看输出。

我可以为您提出建议 - 在您的onReceive()中，只需致电showDialog()并查看是否有效。
如果是 - 那么你的代码就会出错。

!! 另外，如果您在onCreate（）中注册接收者，请不要忘记在onDestroy（）中取消注册！

如何使用AlertDialog Android

1 个答案: