Issue in rendering items in the main thread from a worker thread

Question

I have created a counter app that counts from 0 to infinity until the loop is stopped using a stop button. The app contains 2 buttons(start and stop) and 1 textview. I aim to display the values from 0 to infinity(until the loop is stopped) in the textview. I am using a while loop.

For example, the count value starts from 0 so the while loop starts from 0 and continues until the loop is terminated using the stop button. I want to display values in real time in the textview.

public class MainActivity extends AppCompatActivity {

    boolean start;
    int count=0;


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

        Button bt1=findViewById(R.id.button);
        Button bt2=findViewById(R.id.button2);
        TextView tv=findViewById(R.id.textView);
        Handler h=new Handler(getApplicationContext().getMainLooper());
        

        bt1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                start=true;
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        while(start){
                                count=count+1;
                        }
                        h.post(new Runnable() {
                            @Override
                            public void run() {
                                tv.setText(" "+count);
                            }
                        });
                    }
                }).start();

            }
        });
        bt2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                start=false;
            }
        });
    }
}

The code above is not displaying values in real-time in the textview. What's the issue? Also, should I use a handler or runonUIThread for such tasks?

Help will be appreciated!

Answer 1

You should use runOnUiThread, since the while loop is blocking the UI thread.

runOnUiThread(new Runnable() {
    @Override
    public void run() {
        tv.setText(" "+count);
    }
});

here's the refactored code to get this working.

public class MainActivity extends AppCompatActivity {

    boolean start;
    int count=0;

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

        Button bt1=findViewById(R.id.button);
        Button bt2=findViewById(R.id.button2);
        TextView tv=findViewById(R.id.textView);

        bt1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                start=true;
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        while(start){
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    tv.setText(" "+count);
                                }
                            });
                            count++;
                        }
                    }
                }).start();
            }
        });

        bt2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                start=false;
            }
        });
    }
}