Android -线程问题(随机字符切换到按钮，直到按钮被点击)

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

import java.util.Random;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private Button button;
    private Handler handler;
    private boolean isThreadRunning;

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

        textView = findViewById(R.id.textView);
        button = findViewById(R.id.button);

        handler = new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message msg) {
                if (msg.what == 1) {
                    String randomChar = (String) msg.obj;
                    textView.setText(randomChar);
                }
                return true;
            }
        });

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                isThreadRunning = false;
            }
        });

        startBackgroundThread();
    }

    private void startBackgroundThread() {
        isThreadRunning = true;
        new Thread(new Runnable() {
            @Override
            public void run() {
                Random random = new Random();
                while (isThreadRunning) {
                    char randomChar = (char) (random.nextInt(26) + 'A');
                    String randomString = String.valueOf(randomChar);

                    Message message = handler.obtainMessage(1, randomString);
                    handler.sendMessage(message);

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
}