相关疑难解决方法(0)

我是Android和服务的新手.我的目标是能够设置订阅并在主题字符串上做出版物.解析文本字段的输入后,将设置主题字符串和客户端ID.我正在使用Paho MQTT服务(下载源并构建JAR).

以下导致Null指针异常c.publish().在logcat示出了异常的IMqttDeliveryToken publish(String topic, MqttMessage message, Object userContext, IMqttActionListener callback)在方法MqttAndroidClient被截取的输送令牌其中.

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Set locale;
        l = getResources().getConfiguration().locale;
    }

    @Override
    protected void onResume() {
        super.onResume();
        addButtonListener();        
    }

    private void addButtonListener() {
        Button submitButton = (Button) findViewById(R.id.buttonSubmit);

        submitButton.setOnClickListener(new OnClickListener() {
// ...
// validation code for fields in layout
// ...
// Finally, this.

                    MemoryPersistence mPer = new …