android - 选项卡 Activity 上的 Paho android 服务

Question

我必须制作一个应用程序来阅读 50 个不同的 MQTT 主题，我开始在 android studio 上制作一个带有预定义空 Activity 的演示应用程序并且一切正常，但是一旦我更改为 Tab Activity 我就无法通信与 MQTT 服务器。知道发生了什么吗？

谢谢，

这是连接到 MQTT 服务器的简化代码:

    package com.reonix.tabs_test;

import android.support.design.widget.TabLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import android.widget.Switch;
import android.widget.TextView;
import android.widget.Toast;

import org.eclipse.paho.android.service.MqttAndroidClient;
import org.eclipse.paho.client.mqttv3.IMqttActionListener;
import org.eclipse.paho.client.mqttv3.IMqttToken;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;

public class MainActivity extends AppCompatActivity {

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    private SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will host the section contents.
     */
    private ViewPager mViewPager;

    MqttAndroidClient client;

    String MQTT_HOST = "ssl://mqtt.ddns.net:8883";
    String USERNAME = "admin";
    String PASSWORD = "password";
    String topicStr = "SD/OUTPUT1" ;

    final int timeout = MqttConnectOptions.CONNECTION_TIMEOUT_DEFAULT;
    final int keepalive = MqttConnectOptions.KEEP_ALIVE_INTERVAL_DEFAULT;

    private Switch btnConnect;
    int nSwitch = 15;
    Switch[] switchs = new Switch[nSwitch];

    private TextView subText;

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.container);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);

        mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager));

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        connect();

    }

    public void connect(){
        String clientId = MqttClient.generateClientId();
        client = new MqttAndroidClient(this.getApplicationContext(), MQTT_HOST, clientId);

        try {

            MqttConnectOptions options = new MqttConnectOptions();

            options.setCleanSession(true);
            options.setConnectionTimeout(timeout);
            options.setKeepAliveInterval(keepalive);
            options.setUserName(USERNAME);
            options.setPassword(PASSWORD.toCharArray());

            IMqttToken token = client.connect(options);
            token.setActionCallback(new IMqttActionListener() {
                @Override
                public void onSuccess(IMqttToken asyncActionToken) {
                    // We are connected
                    //Log.d(TAG, "onSuccess");
                    //sub( );
                   // btnConnect.setChecked(true);
                    Toast.makeText(MainActivity.this, "Connected", Toast.LENGTH_LONG).show();

                }

                @Override
                public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                    // Something went wrong e.g. connection timeout or firewall problems
                    //Log.d(TAG, "onFailure");
                    Toast.makeText(MainActivity.this, "Connection Failed", Toast.LENGTH_LONG).show();
                    //btnConnect.setChecked(false);
                }
            });
        } catch (MqttException e) {
            e.printStackTrace();
        }

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        public PlaceholderFragment() {
        }

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            TextView textView = (TextView) rootView.findViewById(R.id.section_label);
            textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
            return rootView;
        }
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a PlaceholderFragment (defined as a static inner class below).
            return PlaceholderFragment.newInstance(position + 1);
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return 3;
        }
    }
}

Answer 1

您的源代码有几个问题:

1. 不要在onCreate 中调用client.connect() 方法(而是只保留MqttAndroidClient 的创建)。该调用的更好位置是 onResume 方法。

2. 您遇到的另一个问题:您正在设置token.setActionCallback()在您调用client.connect() - 所以如果时机不巧，您的回调将不会被调用。

这是你应该尝试的 - 首先定义几个回调:

private MqttConnectOptions mOptions;
private MqttAndroidClient mClient;

private IMqttActionListener mConnectCallback = new IMqttActionListener() {
    @Override
    public void onSuccess(IMqttToken token) {
        Log.d("mConnectCallback onSuccess");
        subscribe();
    }

    @Override
    public void onFailure(IMqttToken token, Throwable ex) {
        Log.d("mConnectCallback onFailure " + ex);
    }
};

private IMqttActionListener mSubscribeCallback = new IMqttActionListener() {
    @Override
    public void onSuccess(IMqttToken token) {
        Log.d("mSubscribeCallback onSuccess");
    }

    @Override
    public void onFailure(IMqttToken token, Throwable ex) {
        Log.d("mSubscribeCallback onFailure " + ex);
    }
};

private IMqttActionListener mPublishCallback = new IMqttActionListener() {
    @Override
    public void onSuccess(IMqttToken token) {
        Log.d("mPublishCallback onSuccess");
    }

    @Override
    public void onFailure(IMqttToken token, Throwable ex) {
        Log.d("mPublishCallback onFailure " + ex);
        disconnect();
        connect();
    }
};

private IMqttMessageListener mMessageListener = new IMqttMessageListener() {
    @Override
    public void messageArrived(String topic, MqttMessage message) throws Exception {
        Log.d("mMessageListener onSuccess topic=" + topic + ", message=" + message);
    }
};

然后定义方法:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mOptions = new MqttConnectOptions();
    mOptions.setCleanSession(true);
    mOptions.setUserName(username);
    mOptions.setPassword(password.toCharArray());
    mClient = new MqttAndroidClient(this, MQTT_HOST, clientId);
}

@Override
public void onResume() {
    super.onResume();
    connect();
}

@Override
public void onPause() {
    super.onPause();
    disconnect();
}

private void connect() {
    try {
        mClient.connect(mOptions, null, mConnectCallback);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

private void disconnect() {
    try {
        mClient.disconnect();
    } catch (Exception ex) {
        ex.printStackTrace();
    }

    mClient.unregisterResources();
}

private void subscribe() {
    try {
        IMqttToken subToken = mClient.subscribe(TOPIC, 1, null, mSubscribeCallback, mMessageListener);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

private void publish() {
    try {
        mClient.publish(topic, new MqttMessage(STR.getBytes()), null, mPublishCallback);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

您可以使用 custom interfaces 在 Activity 和多个 Fragment 之间进行通信.或者使用 LocalBroadcastManager