我必须创建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活动的演示应用程序，一切都运行良好，但是一旦我改为Tab活动，我就无法沟通使用MQTT服务器。知道发生了什么吗？
谢谢，
这是仅用于连接到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;
}
}
}
答案 0 :(得分：0)
您的源代码有几个问题：
请勿在{{1}}中调用client.connect()方法（而只是将MqttAndroidClient创建在那里）。该调用的更好地方是onCreate方法。
您遇到的另一个问题是：您在onResume 之后设置了token.setActionCallback() - 所以如果时机不通，您的回调将不会是调用。
以下是您应该尝试的内容 - 首先使用以下内容定义几个回调：
client.connect()然后定义方法：
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);
}
};
您可以使用custom interfaces在Activity和多个片段之间进行通信。或者使用LocalBroadcastManager