[Date Picker] Avoid re-creating text input picker fragment on configuration changes

Addresses an issue where the input text view was losing entered text and cursor position during configuration changes.

PiperOrigin-RevId: 769580976

Author: Material Design Team

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

@@ -33,7 +33,7 @@
 import android.graphics.drawable.StateListDrawable;
 import android.os.Bundle;
 import androidx.fragment.app.DialogFragment;
-import androidx.fragment.app.FragmentTransaction;
+import androidx.fragment.app.Fragment;
 import androidx.appcompat.content.res.AppCompatResources;
 import android.text.TextUtils;
 import android.view.LayoutInflater;
@@ -96,6 +96,8 @@ public class MaterialDatePicker<S> extends DialogFragment {
   private static final String NEGATIVE_BUTTON_CONTENT_DESCRIPTION_KEY =
       "NEGATIVE_BUTTON_CONTENT_DESCRIPTION_KEY";
   private static final String INPUT_MODE_KEY = "INPUT_MODE_KEY";
+  private static final String CALENDAR_FRAGMENT_TAG = "CALENDAR_FRAGMENT_TAG";
+  private static final String TEXT_INPUT_FRAGMENT_TAG = "TEXT_INPUT_FRAGMENT_TAG";
 
   static final Object CONFIRM_BUTTON_TAG = "CONFIRM_BUTTON_TAG";
   static final Object CANCEL_BUTTON_TAG = "CANCEL_BUTTON_TAG";
@@ -502,22 +504,27 @@ private String getHeaderContentDescription() {
 
   private void startPickerFragment() {
     int themeResId = getThemeResId(requireContext());
-    calendar =
-        MaterialCalendar.newInstance(
-            getDateSelector(), themeResId, calendarConstraints, dayViewDecorator);
-
-    pickerFragment =
-        inputMode == INPUT_MODE_TEXT
-            ? MaterialTextInputPicker.newInstance(
-                getDateSelector(), themeResId, calendarConstraints)
-            : calendar;
-    updateTitle();
-    updateHeader(getHeaderText());
-
-    FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
-    fragmentTransaction.replace(R.id.mtrl_calendar_frame, pickerFragment);
-    fragmentTransaction.commitNow();
+    String currentTag =
+        inputMode == INPUT_MODE_TEXT ? TEXT_INPUT_FRAGMENT_TAG : CALENDAR_FRAGMENT_TAG;
+
+    Fragment foundFragment = getChildFragmentManager().findFragmentByTag(currentTag);
+    @SuppressWarnings("unchecked")
+    PickerFragment<S> fragment =
+        foundFragment instanceof PickerFragment ? (PickerFragment<S>) foundFragment : null;
+
+    if (fragment == null) {
+      if (inputMode == INPUT_MODE_TEXT) {
+        fragment =
+            MaterialTextInputPicker.newInstance(getDateSelector(), themeResId, calendarConstraints);
+      } else {
+        calendar =
+            MaterialCalendar.newInstance(
+                getDateSelector(), themeResId, calendarConstraints, dayViewDecorator);
+        fragment = calendar;
+      }
+    }
 
+    pickerFragment = fragment;
     pickerFragment.addOnSelectionChangedListener(
         new OnSelectionChangedListener<S>() {
           @Override
@@ -531,6 +538,14 @@ public void onIncompleteSelectionChanged() {
             confirmButton.setEnabled(false);
           }
         });
+
+    updateTitle();
+    updateHeader(getHeaderText());
+
+    getChildFragmentManager()
+        .beginTransaction()
+        .replace(R.id.mtrl_calendar_frame, pickerFragment, currentTag)
+        .commitNow();
   }
 
   private void initHeaderToggle(Context context) {

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

@@ -238,7 +238,7 @@ public View onCreateTextInputView(
       // Move the cursor to the end of the text field
       CharSequence text = startEditText.getText();
       if (text != null) {
-        startEditText.post(() -> startEditText.setSelection(text.length()));
+        startEditText.setSelection(text.length());
       }
     }
     if (selectedEndItem != null) {

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

@@ -138,7 +138,7 @@ public View onCreateTextInputView(
       // Move the cursor to the end of the text field
       CharSequence text = dateEditText.getText();
       if (text != null) {
-        dateEditText.post(() -> dateEditText.setSelection(text.length()));
+        dateEditText.setSelection(text.length());
       }
     }
 

lib/java/com/google/android/material/datepicker/res/layout/mtrl_picker_text_input_date.xml

@@ -32,6 +32,7 @@
       android:layout_gravity="center_horizontal">
 
     <com.google.android.material.textfield.TextInputEditText
+        android:id="@+id/mtrl_picker_edit_text_date"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:hint="@string/mtrl_picker_text_input_date_hint"

lib/java/com/google/android/material/datepicker/res/layout/mtrl_picker_text_input_date_range.xml

@@ -35,6 +35,7 @@
         android:layout_gravity="center_horizontal">
 
       <com.google.android.material.textfield.TextInputEditText
+          android:id="@+id/mtrl_picker_edit_text_range_start"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:hint="@string/mtrl_picker_text_input_date_range_start_hint"
@@ -55,6 +56,7 @@
         android:layout_gravity="center_horizontal">
 
       <com.google.android.material.textfield.TextInputEditText
+          android:id="@+id/mtrl_picker_edit_text_range_end"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:hint="@string/mtrl_picker_text_input_date_range_end_hint"