Handler not updating UI

Question

First of all, Im new to android. So i was displaying the current time on a TextView in the MainActivity.java using a Handler, which worked just fine. Then i used a TimePicker(which is actually in another activity, TimeActivity.java) to pick a time, at which the time stops.

For example, if the time picked using the TimePicker is 8:30, the time in TextView will cease to advance further beyond 8:30

Also theres a STOP button with which calls handler.removeMessages(0); to stop the handler and hence the time.

• The problem is, when i come back from TimeActivity.java, the TextView is blank which looks like the handler is not running but it successfully Toasts "Time Stopped" when the time's hit. Whats this anomaly?
• I happen to face another problem, The Toast, "Time stopped" in stopTime() prevails on the screen for an abnormally longer period of time but it's normal with the Toast in stop(View v) even though i used the same logic to stop the handler in both methods. What's causing this?

Here's my MainActivity.java

import static com.gamecodeschool.broadcast.TimeActivity.minute1;

public class MainActivity extends AppCompatActivity {

Button start,stop,set;
TextView textView;
final Handler handler = new Handler();
Runnable r;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Views
    textView = (TextView)findViewById(R.id.textView);
    start = (Button)findViewById(R.id.button);
    stop = (Button)findViewById(R.id.button2);
    set = (Button)findViewById(R.id.button3);

    set.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v){
            Intent intent = new Intent(getApplicationContext(),TimeActivity.class);
            startActivity(intent);
        }
    });
}

public void stop(View v) {
    handler.removeMessages(0);
    Toast.makeText(this,"Stopped",Toast.LENGTH_SHORT).show();
}

public void runInBackground(View v) {
    handler.post(r);
    r = new Runnable() {
        @Override
        public void run() {
            //String time = java.text.DateFormat.getDateTimeInstance().format(new Date());
            Calendar calendar = Calendar.getInstance();
            int hour = calendar.get(Calendar.HOUR_OF_DAY);
            int minute = calendar.get(Calendar.MINUTE);
            StringBuilder stringBuilder = new StringBuilder().append(hour).append(":").append(minute);
            textView.setText(stringBuilder);
            if (minute==minute1){
                stopTime();
            }
            handler.postDelayed(this,100);
        }
    };
}

private void stopTime() {
    handler.removeMessages(0);
    Toast.makeText(this,"Time Stopped",Toast.LENGTH_SHORT).show();
} }

And Here's my TimeActivity

public class TimeActivity extends AppCompatActivity {

TimePicker timePicker;
Button button;
TextView textView;
StringBuilder stringBuilder;
static int hour1,minute1;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_time);

    timePicker = (TimePicker)findViewById(R.id.timePicker);
    button = (Button)findViewById(R.id.saveButton);
    textView = (TextView)findViewById(R.id.timeView);
    Calendar calendar = Calendar.getInstance();
    int hour = calendar.get(Calendar.HOUR_OF_DAY);
    int minute = calendar.get(Calendar.MINUTE);
    showTime(hour,minute);
}

private void showTime(int hour, int minute) {
    stringBuilder = new StringBuilder().append(hour).append(":").append(minute);
    textView.setText(stringBuilder);
}

public void saveTime(View v){
    hour1 = timePicker.getHour();
    minute1 = timePicker.getMinute();
    showTime(hour1,minute1);
    Toast.makeText(TimeActivity.this,hour1+":"+minute1,Toast.LENGTH_SHORT).show();
    Intent intent = new Intent(this,MainActivity.class);
    startActivity(intent);
} }

Answer 1

Updating UI must be done on the UIThread, for instance to update your TextViewyou should for example :

public void runInBackground(View v) {
    handler.post(r);
    r = new Runnable() {
        @Override
        public void run() {
            //String time = java.text.DateFormat.getDateTimeInstance().format(new Date());
            Calendar calendar = Calendar.getInstance();
            int hour = calendar.get(Calendar.HOUR_OF_DAY);
            int minute = calendar.get(Calendar.MINUTE);
            StringBuilder stringBuilder = new StringBuilder().append(hour).append(":").append(minute);
            runOnUiThread(new Runnable() {
                @Override public void run() {
                    textView.setText(stringBuilder);
                }
            });
            textView.setText(stringBuilder);
            if (minute==minute1){
                stopTime();
            }
            handler.postDelayed(this,100);
        }
    };
}