Android：Thread Runnable和Handler.post问题-Run方法中（（Handler.postXX预期无法按时运行））

Question

I have a TCP Socket used as a TCP client which is used to read incoming data from a server constantly -- until the client or the server drops the connection. I don't know of any other way but use a while (true) loop in a different Runnable thread and in it (in the while loop) check for incoming data. The received data needs to be printed in an EditText .

The problem I am having is updating the text from Handler.post(...) .

I know that:

• In order to create TCP connections with Android 3.0 and above, I am required to place the TCP code either in a new Thread(...) or an AsyncTask because Strict mode has been enabled by default and I do not want to disable it.

• I know that in order to update the UI from a new Thread in Android, I need to use Handler.post() if I use a Thread or the onProgressUpdate via publichProgress if I use AsyncTask and I know how to use all these but I am experiencing weird frustrating issues with both of them.

So, all I want to do is:

• Listen to the server permanently
• As soon as the server sends me a message, example: 'w' or 'a' or n', I immidiately display it on the EditText. You can think of it as a telnet session but I need "more" precision than telnet as I want to process every single byte, even non-printable ones so I do not want to use readLine in anyway. I must read a byte at a time OR get a buffer of bytes and then process them separately by iterating through the buffer. I went with a byte at a time.

Here is the code I have and please pay attention to my comment above handle.response to see the problem I am having. I hope you can clear this out.

The code is very briefly coded and I have removed a lot of the error checking sections for this sample.

I have a new class called: ThreadClientInput:

public class ThreadClientInput  implements Runnable {

InputStream inputStream;
MainActivity mainActivity;
Handler handler = new Handler();
int NextByte = 0;

public ThreadClientInput(MainActivity ma)
{
    mainActivity = ma;
}

@Override
public void run() 
{ 
    ////////////////////////////////////////////////////////////////
    // Run the sensitive code that requires us to create this thread
    try {
        mainActivity.tcp_Client = new Socket("192.168.1.90", 23);
    }
    catch (Exception e){Log.e("EXEPTION:", e.getMessage().toString());return;}
    ////////////////////////////////////////////////////////////////


    // Only try to get the inputStream if we have a successful connection
    if (mainActivity.tcp_Client != null) 
    {
        try 
        {
            inputStream = mainActivity.tcp_Client.getInputStream();
        }
        catch (Exception e){Log.e("EXEPTION:", e.getMessage().toString()); return;}
    }


    /////////////////////////////////////////////
    /////////////////////////////////////////////
    // Update the text on the "Connect" button
    handler.post(new Runnable() 
    {
        @Override
        public void run() 
        { mainActivity.btn_Connect.setText("Connected");}
    });
    /////////////////////////////////////////////
    /////////////////////////////////////////////

    try 
    {   

        // I need to constantly read the data until we manually disconnect or
        // the server drops the connection
        while (true) 
        {
            // Get the next byte
            // I do not want to use "readline()" from a BufferedReader etc because I need to know exactly what's coming in
            // I need to process every single byte
            NextByte = inputStream.read();

            if (NextByte > -1)
            {
                Log.e("in (While loop):", Character.toString((char)NextByte));

                *** Here is the problem ****
                // Update the EditText and this is where the problem starts
                // if the server sends "1234", the Log.e() above will display everything correctly: "1234"
                // however the handler.post below will run at the end of the last byte so the
                // the EditText as well as the second Log.e below within the handle.post will display: "1444" or "4444" or "2444"
                // So the handler.post does *not* run immediately even if I try handle.postAtFrontOfQueue()
                // If the server sends "12345678", again, Log.e() above will display everything correctly: "12345678" 
                // however the handler.post below will run at the end of the last byte again
                // and I will get "88888888" (most of the time) or "18888888" 

                //   

                handler.post(new Runnable() 
                {
                    @Override
                    public void run() 
                    {
                        mainActivity.et_Response.setText(mainActivity.et_Response.getText() + Character.toString((char)NextByte));
                        Log.e("In handler.post:", Character.toString((char)NextByte));
                    }
                });
            }
        }           
    }
    catch (Exception e){Log.e("EXEPTION:", e.getMessage().toString());}
}}

I tried various variations including one with runOnUiThread and AsyncTask, with all I am getting same results. I am out, I have nothing. At this point of time I am just reading some documentation about Handle.post method to see if I can make sense.

I hope you have a solution and I know that " while (true) " isn't a good practice but I can break the loop from outside the thread with setting a flag and I don't know of any other way how to do this.

Answer 1

I am not sure how you are able to access NextByte from public void run() without defining it as final !?

• If you want the handler to post message to the Activity UI thread, yo should create it within the activity class so it can access its Looper.

I can think of two solutions for your problem as follows:

1- To use a custom Runnable class where you pass to it the NextByte value as variable eg

   handler.post(new MyRunnable(NextByte));

And MyRunnable can be something like:

  class MyRunnable implements Runnable{
   int byteData;  
   public MyRunnable(int byteData){
      this.byteData = byteData;
   }

     public void run(){ // update the EditText}
  }                          

2- To use handler.sendMessage(); and add the NextByte as the message argument eg

 Message msg = new Message();
 msg.arg1 = NextBye
 handler.sendMessage(msg);

And your handler should be defined as following:

handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            int nextByte = msg.arg1;
                            // update the EditText
        }
    };

Answer 2

Problem has been resolved.

This is what I did this.

In MainActivity.java which is the main file, in class MainActivity

    public static class MyRunnable implements Runnable {
    int currentByte = 0;

    public MyRunnable(int b){
        currentByte = b;
    }

    @Override
    public void run() 
    {
        mainActivity.et_Response.setText(mainActivity.et_Response.getText() + Character.toString((char)currentByte));
    }
}

I have a statement mainActivity = this; in onCreate and then in ThreadClientInput.run

        try {
        while (true)
        {
            NextByte = inputStream.read(); 

            // if the server drops the connection, break out the loop
            if (NextByte < 0) break;

            handler.post(new MainActivity.MyRunnable(NextByte));
        }
    }
    catch (Exception e) {
        Log.e("EXCEPTION", e.getMessage());
    }

After this, handler.post is getting called correctly and at the correct and expected time. Full credit goes to iTech.