Ensure handlers use main looper and clean up callbacks

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/alerts/alertdialog/AlertDialogActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -13,7 +14,7 @@
 import com.google.android.material.dialog.MaterialAlertDialogBuilder;
 
 public class AlertDialogActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityAlertDialogBinding binding;
 
     @Override
@@ -45,4 +46,11 @@ private MaterialAlertDialogBuilder createAlertDialog() {
                 .setPositiveButton(android.R.string.ok, null)
                 .setNegativeButton(android.R.string.cancel, null);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/alerts/snackbar/SnackBarActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -13,7 +14,7 @@
 import com.google.android.material.snackbar.Snackbar;
 
 public class SnackBarActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivitySnackBarBinding binding;
 
     @Override
@@ -39,4 +40,11 @@ protected void onCreate(Bundle savedInstanceState) {
 
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/alerts/toast/ToastActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 import android.widget.Toast;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
@@ -13,7 +14,7 @@
 import com.d4rk.androidtutorials.java.utils.EdgeToEdgeDelegate;
 
 public class ToastActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityToastBinding binding;
 
     @Override
@@ -37,4 +38,11 @@ protected void onCreate(Bundle savedInstanceState) {
 
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/buttons/buttons/ButtonsActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -14,7 +15,7 @@
 import me.zhanghai.android.fastscroll.FastScrollerBuilder;
 
 public class ButtonsActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityButtonsBinding binding;
 
     @Override
@@ -48,4 +49,11 @@ protected void onCreate(Bundle savedInstanceState) {
         binding.floatingButtonShowSyntax.setOnClickListener(v -> startActivity(new Intent(ButtonsActivity.this, ButtonsCodeActivity.class)));
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/buttons/image/ImageButtonsActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -13,7 +14,7 @@
 import com.google.android.material.snackbar.Snackbar;
 
 public class ImageButtonsActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityImageButtonsBinding binding;
 
     @Override
@@ -37,4 +38,11 @@ protected void onCreate(Bundle savedInstanceState) {
 
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/buttons/radio/RadioButtonsActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 import android.widget.RadioButton;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
@@ -13,7 +14,7 @@
 import com.google.android.material.snackbar.Snackbar;
 
 public class RadioButtonsActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityRadioButtonsBinding binding;
 
     @Override
@@ -38,4 +39,11 @@ protected void onCreate(Bundle savedInstanceState) {
 
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/buttons/switches/SwitchActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -15,7 +16,7 @@
 import me.zhanghai.android.fastscroll.FastScrollerBuilder;
 
 public class SwitchActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivitySwitchBinding binding;
 
     @Override
@@ -43,4 +44,11 @@ private void setOnClickListeners() {
         });
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/clocks/chronometer/ChronometerActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 import android.os.SystemClock;
 
 import androidx.annotation.Nullable;
@@ -13,7 +14,7 @@
 import com.d4rk.androidtutorials.java.utils.EdgeToEdgeDelegate;
 
 public class ChronometerActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityChronometerBinding binding;
 
     @Override
@@ -36,4 +37,11 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
         binding.buttonStop.setOnClickListener(v -> binding.chronometer.stop());
         binding.buttonReset.setOnClickListener(v -> binding.chronometer.setBase(SystemClock.elapsedRealtime()));
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/clocks/clock/ClockActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -12,7 +13,7 @@
 import me.zhanghai.android.fastscroll.FastScrollerBuilder;
 
 public class ClockActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityClockBinding binding;
 
     @Override
@@ -29,4 +30,11 @@ protected void onCreate(Bundle savedInstanceState) {
         binding.floatingButtonShowSyntax.setOnClickListener(view -> startActivity(new Intent(this, ClockCodeActivity.class)));
         handler.postDelayed(() -> binding.floatingButtonShowSyntax.shrink(), 5000);
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/clocks/datepicker/DatePickerActivity.java

@@ -4,6 +4,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -16,7 +17,7 @@
 import java.util.Locale;
 
 public class DatePickerActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private final Calendar calendar = Calendar.getInstance();
     private final SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy", Locale.getDefault());
     private ActivityDatePickerBinding binding;
@@ -54,4 +55,11 @@ protected void onCreate(Bundle savedInstanceState) {
     private void updateDateInView() {
         binding.dateTextView.setText(dateFormat.format(calendar.getTime()));
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/clocks/timepicker/TimePickerActivity.java

@@ -4,6 +4,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 
 import com.d4rk.androidtutorials.java.ui.components.navigation.UpNavigationActivity;
 
@@ -16,7 +17,7 @@
 import java.util.Locale;
 
 public class TimePickerActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private final Calendar calendar = Calendar.getInstance();
     private ActivityTimePickerBinding binding;
 
@@ -56,4 +57,11 @@ private void updateTimeInView() {
         SimpleDateFormat sdf = new SimpleDateFormat(timeFormat, Locale.getDefault());
         binding.timeTextView.setText(sdf.format(calendar.getTime()));
     }
-}
+
+
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        handler.removeCallbacksAndMessages(null);
+    }
+}

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/data/room/RoomActivity.java

@@ -3,6 +3,7 @@
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.Looper;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -26,7 +27,7 @@
  * Demonstrates basic Room usage by inserting and reading notes.
  */
 public class RoomActivity extends UpNavigationActivity {
-    private final Handler handler = new Handler();
+    private final Handler handler = new Handler(Looper.getMainLooper());
     private ActivityRoomBinding binding;
     private NotesAdapter adapter;
     private AppDatabase db;
@@ -82,6 +83,7 @@ private void loadNotes() {
     protected void onDestroy() {
         super.onDestroy();
         executor.shutdown();
+        handler.removeCallbacksAndMessages(null);
     }
 
     private static class NotesAdapter extends RecyclerView.Adapter<NotesAdapter.NoteViewHolder> {
@@ -119,4 +121,5 @@ static class NoteViewHolder extends RecyclerView.ViewHolder {
             }
         }
     }
+
 }