从子线程到主线程的Android通信

Question

我有一个带有主线程和子线程的android应用程序。我需要子线程定期向主线程发送消息。主线程依次更新UI。我曾尝试使用处理程序、获取消息((和发送消息((等来完成此过程，但当主线程更新textView时，我的应用程序失败了，即使我将收到的消息打印到日志中，这也很好。

所以我尝试了另一种方法，在子线程中发布一个可运行的程序来更新UI

在主线程中：

public class Example extends Activity {
    public TextView mMatchesText;
    public Handler mHandler;  
    private ServerConnection conn;
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mMatchesText = (TextView) Example.this.findViewById(R.id.matches);
        mMatchesText.setText("Matches:n");     /*this text appears when I run the app*/
        mHandler = new Handler();
        SessionEvents.addAuthListener(new SampleAuthListener());
 public class SampleAuthListener implements AuthListener {
        public void onAuthSucceed() {
            Example.this.runOnUiThread(new Runnable() {
                    public void run() {
                        conn = new ServerConnection(mProfile.toString());
                    }
                });
        }
   }

在子线程(ServerConnection.java(中：

/* constructor */
public ServerConnection()
{
    runner = new Thread(this);
    runner.start();
}

public void run()
{
    String fromServer;
    /** Establish connection to the server */
    /** Wait for messages from the server */
    while((fromServer = inFromServer.readLine()) != null)
    {
        mHandler.post(new Runnable(){
            @Override
            public void run(){
                Log.e("MY APP", fromServer);
                mMatchesText.setText(fromServer); 
            }
        });
    }
}

应用程序在第56行再次失败，该行为mMatcheText.setText(fromServer(formServer不为空，因为我将其打印到LogCat，并且它确实包含服务器发送的数据。

    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): FATAL EXCEPTION: main
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): java.lang.NullPointerException
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): at com.facebook.android.ServerConnection$1.run(ServerConnection.java:56) <--this is mMatches..
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): at android.os.Handler.handleCallback(Handler.java:587)
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): at android.os.Handler.dispatchMessage(Handler.java:92)
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): at android.os.Looper.loop(Looper.java:130)
    11-24 08:02:49.622: ERROR/AndroidRuntime(14571): at 

android.app.ActivityThread.main(ActivityThreads.java：3683(

为了以防万一，mMatchsText在main.xml中声明如下：

<TextView android:id="@+id/matches"
android:textColor="@drawable/black"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/Login"
android:text=""
/>

有人能帮忙吗？

Answer 1

mMatchesText在此处使用时为空：mMatchesText.setText(fromServer);

除非你向我们展示你对它的初始化，否则我们只能帮你。

Answer 2

这就是我在所有应用程序中的做法。制作一个像这样的自定义Runnable类

public abstract class MyRunnable implements Runnable {
    public Object data;
    public MyRunnable setData(Object data){
        this.data=data;
        return this;
    }
    public MyRunnable setData(Object... dataArr){
        data=dataArr;
        return this;
    }
}

然后您可以使用它将数据发送到Runnable

//this is you code from question, i modified the use of runnable and String fromServer
public void run()
{
    String fromServer;
    /** Establish connection to the server */
    /** Wait for messages from the server */
    while((fromServer = inFromServer.readLine()) != null)
    {
        mHandler.post(new MyRunnable(){
            @Override
            public void run(){
                //here variable fromServer is not available inside the Runnable object
                String fromServerCpy=(String)data;//getting the fromServer sent to MyRunnable
                Log.e("MY APP", fromServerCpy);
                mMatchesText.setText(fromServerCpy); 
            }
        }.setData(fromServer));// !!! sending fromServer to MyRunnable data variable
    }
}