Question

I start a thread in activity. There is a constructor textview in thread. It has no error of setText when update the textview in run.

But if I new a thread without parameter, then setTextView (TextView) and setText() in run.. There is the error.

Why it can appear this?

Edit: My code

package extthread;

import android.widget.TextView;

public class MyUpdateUIThread extends Thread {

private TextView textView1;

public MyUpdateUIThread(TextView textView1) {
super();
this.textView1 = textView1;
}

@Override
public void run() {
super.run();
textView1.setText("zzzzzzzzzzzzzz");
}

}

------------------------------
package testtest.test.run;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import extthread.MyUpdateUIThread;

public class Main extends Activity {
TextView textView;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

textView = (TextView) this.findViewById(R.id.textView1);
Thread thread = new Thread(new MyUpdateUIThread(textView));
thread.start();

}
};

Answer 1

Use runOnUiThread inside run method of Thread for updating TextView as:

Your_Current_Activity.this.runOnUiThread(new Runnable() {
    public void run() {

             //update textview here
    }
});

EDIT :

as in your current code Thread is from separate class . then you will need to pass Main Activity instance to Thread class to access runOnUiThread in MyUpdateUIThread thread . change your MyUpdateUIThread class constructor as:

private TextView textView1;
Activity activity;
public MyUpdateUIThread(TextView textView1,Activity activity) {
super();
this.textView1 = textView1;
this.activity=activity;
}

@Override
public void run() {
super.run();
activity.runOnUiThread(new Runnable() {
    public void run() {

       //update textview here
       textView1.setText("zzzzzzzzzzzzzz");
    }
});

}

and create MyUpdateUIThread object in Main Activity as:

Thread thread = new Thread(new MyUpdateUIThread(textView,Main.this));