[DatePicker] Make picker not final and expose onPositiveButtonClick and onNegativeButtonClick

Resolves #1688

PiperOrigin-RevId: 651106986

Author: paulfthomas

lib/java/com/google/android/material/datepicker/MaterialDatePicker.java

@@ -74,7 +74,7 @@
  * developer guidance and design
  * guidelines.
  */
-public final class MaterialDatePicker<S> extends DialogFragment {
+public class MaterialDatePicker<S> extends DialogFragment {
 
   private static final String OVERRIDE_THEME_RES_ID = "OVERRIDE_THEME_RES_ID";
   private static final String DATE_SELECTOR_KEY = "DATE_SELECTOR_KEY";
@@ -344,17 +344,7 @@ public final View onCreateView(
       confirmButton.setContentDescription(
           getContext().getResources().getText(positiveButtonContentDescriptionResId));
     }
-    confirmButton.setOnClickListener(
-        new View.OnClickListener() {
-          @Override
-          public void onClick(View v) {
-            for (MaterialPickerOnPositiveButtonClickListenersuper S> listener :
-                onPositiveButtonClickListeners) {
-              listener.onPositiveButtonClick(getSelection());
-            }
-            dismiss();
-          }
-        });
+    confirmButton.setOnClickListener(this::onPositiveButtonClick);
 
     Button cancelButton = root.findViewById(R.id.cancel_button);
     cancelButton.setTag(CANCEL_BUTTON_TAG);
@@ -369,19 +359,35 @@ public void onClick(View v) {
       cancelButton.setContentDescription(
           getContext().getResources().getText(negativeButtonContentDescriptionResId));
     }
-    cancelButton.setOnClickListener(
-        new View.OnClickListener() {
-          @Override
-          public void onClick(View v) {
-            for (View.OnClickListener listener : onNegativeButtonClickListeners) {
-              listener.onClick(v);
-            }
-            dismiss();
-          }
-        });
+    cancelButton.setOnClickListener(this::onNegativeButtonClick);
     return root;
   }
 
+  /**
+   * Called when the positive button on the picker has been clicked.
+   *
+   * @param view The view that was clicked.
+   */
+  public void onPositiveButtonClick(@NonNull View view) {
+    for (MaterialPickerOnPositiveButtonClickListenersuper S> listener :
+        onPositiveButtonClickListeners) {
+      listener.onPositiveButtonClick(getSelection());
+    }
+    dismiss();
+  }
+
+  /**
+   * Called when the negative button on the picker has been clicked.
+   *
+   * @param view The view that was clicked.
+   */
+  public void onNegativeButtonClick(@NonNull View view) {
+    for (View.OnClickListener listener : onNegativeButtonClickListeners) {
+      listener.onClick(view);
+    }
+    dismiss();
+  }
+
   @Override
   public void onStart() {
     super.onStart();