Question

我有一个Smarthome毕业项目，它使用MQTT协议与云和一个控制它的Android应用程序进行通信。

我试图仅创建一个MqttAndroidClient并在所有活动中使用它并且不起作用，当我尝试将同一个客户端传递给另一个发布或订阅方法时，我收到错误类

    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.badr.said.muhammad.smarthome/com.badr.said.muhammad.smarthome.Welcome}: java.lang.NullPointerException: Attempt to invoke virtual method 'org.eclipse.paho.client.mqttv3.IMqttDeliveryToken org.eclipse.paho.android.service.MqttService.publish(java.lang.String, java.lang.String, byte[], int, boolean, java.lang.String, java.lang.String)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)

这是发生错误的代码

public class Welcome extends AppCompatActivity {

MqttAndroidClient client;

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

    client = new MqttAndroidClient(this.getApplicationContext(),mqtthost,clientId);
    MqttConnectOptions options = new MqttConnectOptions();
    options.setUserName(username);
    options.setPassword(password.toCharArray());

    try {
        IMqttToken token = client.connect(options);
        token.setActionCallback(new IMqttActionListener() {
            @Override
            public void onSuccess(IMqttToken asyncActionToken) {
                Toast.makeText(Welcome.this, "Connected !", Toast.LENGTH_LONG).show();
            }

            @Override
            public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                Toast.makeText(Welcome.this, "Connection Field , Check Your Internet Network !", Toast.LENGTH_LONG).show();

            }
        });

    } catch (MqttException e) {
        e.printStackTrace();
    }

    pub("Smarthome","check",client);
    sub5(client);

但是在某些切换按钮上使用相同的pub和sub5方法传递MqttAndroidClient作为参数，它的工作方式与此代码类似

toggle.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if (isChecked) {
                pub("Smarthome", "devicegon1", client);
            } else {
                pub("Smarthome", "devicegoff1", client);
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            sub();
        }
    });

那有什么不对，有什么想法或帮助吗？

Answer 1

您在调用pub()之前呼叫onSuccess()，因此当您尝试发布时，您尚未实际连接。

将pub()和sub5()移到该回调中，事情应该改进

为什么我不能为整个Android应用程序安装一个MqttAndroidClient？

1 个答案: