[Tab] Fixed indicator not updating when a tab to the start/left of the selected tab is removed.

PiperOrigin-RevId: 456322731

Author: pekingme

catalog/java/io/material/catalog/tabs/TabsScrollableDemoFragment.java

@@ -18,6 +18,8 @@
 
 import io.material.catalog.R;
 
+import static java.lang.Math.max;
+
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -87,14 +89,23 @@ public View onCreateDemoView(
           numTabs++;
         });
 
-    Button removeButton = view.findViewById(R.id.remove_tab_button);
-    removeButton.setOnClickListener(
+    Button removeFirstButton = view.findViewById(R.id.remove_first_tab_button);
+    removeFirstButton.setOnClickListener(
+        v -> {
+          if (scrollableTabLayout.getTabCount() > 0) {
+            scrollableTabLayout.removeTabAt(0);
+          }
+          numTabs = max(0, numTabs - 1);
+        });
+
+    Button removeLastButton = view.findViewById(R.id.remove_last_tab_button);
+    removeLastButton.setOnClickListener(
         v -> {
           Tab tab = scrollableTabLayout.getTabAt(scrollableTabLayout.getTabCount() - 1);
           if (tab != null) {
             scrollableTabLayout.removeTab(tab);
           }
-          numTabs = Math.max(0, numTabs - 1);
+          numTabs = max(0, numTabs - 1);
         });
     return view;
   }

catalog/java/io/material/catalog/tabs/res/layout/cat_tabs_scrollable_fragment.xml

@@ -32,6 +32,14 @@
       android:layout_marginBottom="@dimen/cat_tabs_standard_spacing"
       android:orientation="vertical">
 
+    <Button
+      android:id="@+id/add_tab_button"
+      android:layout_width="wrap_content"
+      android:layout_height="wrap_content"
+      android:layout_marginEnd="@dimen/cat_tabs_small_spacing"
+      android:layout_marginRight="@dimen/cat_tabs_small_spacing"
+      android:text="@string/cat_tabs_add_tab_button_label" />
+
     <LinearLayout
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
@@ -40,17 +48,17 @@
         android:orientation="horizontal"
         tools:ignore="ButtonStyle">
       <Button
-          android:id="@+id/add_tab_button"
+          android:id="@+id/remove_first_tab_button"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_marginEnd="@dimen/cat_tabs_small_spacing"
           android:layout_marginRight="@dimen/cat_tabs_small_spacing"
-          android:text="@string/cat_tabs_add_tab_button_label" />
+          android:text="@string/cat_tabs_remove_first_tab_button_label" />
       <Button
-          android:id="@+id/remove_tab_button"
+          android:id="@+id/remove_last_tab_button"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
-          android:text="@string/cat_tabs_remove_tab_button_label" />
+          android:text="@string/cat_tabs_remove_last_tab_button_label" />
     </LinearLayout>
 
 

catalog/java/io/material/catalog/tabs/res/values/strings.xml

@@ -45,6 +45,8 @@
   <string name="cat_tabs_secondary_tabs_label">Material Tabs (Secondary)</string>
   <string name="cat_tabs_add_tab_button_label">Add Tab</string>
   <string name="cat_tabs_remove_tab_button_label">Remove Tab</string>
+  <string name="cat_tabs_remove_first_tab_button_label">Remove First Tab</string>
+  <string name="cat_tabs_remove_last_tab_button_label">Remove Last Tab</string>
   <string name="cat_tabs_controllable_demo_title">Controllable Tabs Demo</string>
   <string name="cat_tabs_scrollable_demo_title">Scrollable Tabs Demo</string>
   <string name="cat_tabs_auto_demo_title">Auto Tabs Demo</string>

lib/java/com/google/android/material/tabs/TabLayout.java

@@ -25,8 +25,6 @@
 import static com.google.android.material.animation.AnimationUtils.FAST_OUT_SLOW_IN_INTERPOLATOR;
 import static com.google.android.material.theme.overlay.MaterialThemeOverlay.wrap;
 
-import android.animation.Animator;
-import android.animation.AnimatorListenerAdapter;
 import android.animation.ValueAnimator;
 import android.annotation.SuppressLint;
 import android.content.Context;
@@ -3007,10 +3005,6 @@ private float approximateLineWidth(@NonNull Layout layout, int line, float textS
 
   class SlidingTabIndicator extends LinearLayout {
     ValueAnimator indicatorAnimator;
-    int selectedPosition = -1;
-    // selectionOffset is only used when a tab is being slid due to a viewpager swipe.
-    // selectionOffset is always the offset to the right of selectedPosition.
-    float selectionOffset;
 
     private int layoutDirection = -1;
 
@@ -3038,26 +3032,21 @@ boolean childrenNeedLayout() {
     /**
      * Set the indicator position based on an offset between two adjacent tabs.
      *
-     * @param position The position from which the offset should be calculated.
-     * @param positionOffset The offset to the right of position where the indicator should be
-     *     drawn. This must be a value between 0.0 and 1.0.
+     * @param position Position index of the first tab (with less index) currently being displayed.
+     *     Tab position+1 will be visible if positionOffset is nonzero.
+     * @param positionOffset Value from [0, 1) indicating the offset from the tab at position.
      */
     void setIndicatorPositionFromTabPosition(int position, float positionOffset) {
       if (indicatorAnimator != null && indicatorAnimator.isRunning()) {
         indicatorAnimator.cancel();
       }
 
-      selectedPosition = position;
-      selectionOffset = positionOffset;
+      // The title view refers to the one indicated when offset is 0.
+      final View firstTitle = getChildAt(position);
+      // The title view refers to the one indicated when offset is 1.
+      final View nextTitle = getChildAt(position + 1);
 
-      final View selectedTitle = getChildAt(selectedPosition);
-      final View nextTitle = getChildAt(selectedPosition + 1);
-
-      tweenIndicatorPosition(selectedTitle, nextTitle, selectionOffset);
-    }
-
-    float getIndicatorPosition() {
-      return selectedPosition + selectionOffset;
+      tweenIndicatorPosition(firstTitle, nextTitle, positionOffset);
     }
 
     @Override
@@ -3144,7 +3133,7 @@ protected void onLayout(boolean changed, int l, int t, int r, int b) {
         // position of the indicator, since the tab widths are different. We need to modify the
         // animation's updateListener to pick up the new target positions.
         updateOrRecreateIndicatorAnimation(
-            /* recreateAnimation= */ false, selectedPosition, /* duration= */ -1);
+            /* recreateAnimation= */ false, getSelectedTabPosition(), /* duration= */ -1);
       } else {
         // If we've been laid out, update the indicator position
         jumpIndicatorToSelectedPosition();
@@ -3153,7 +3142,7 @@ protected void onLayout(boolean changed, int l, int t, int r, int b) {
 
     /** Immediately update the indicator position to the currently selected position. */
     private void jumpIndicatorToSelectedPosition() {
-      final View currentView = getChildAt(selectedPosition);
+      final View currentView = getChildAt(getSelectedTabPosition());
       tabIndicatorInterpolator.setIndicatorBoundsForTab(
           TabLayout.this, currentView, tabSelectedIndicator);
     }
@@ -3214,7 +3203,7 @@ void animateIndicatorToPosition(final int position, int duration) {
      */
     private void updateOrRecreateIndicatorAnimation(
         boolean recreateAnimation, final int position, int duration) {
-      final View currentView = getChildAt(selectedPosition);
+      final View currentView = getChildAt(getSelectedTabPosition());
       final View targetView = getChildAt(position);
       if (targetView == null) {
         // If we don't have a view, just update the position now and return
@@ -3239,18 +3228,6 @@ public void onAnimationUpdate(@NonNull ValueAnimator valueAnimator) {
         animator.setDuration(duration);
         animator.setFloatValues(0F, 1F);
         animator.addUpdateListener(updateListener);
-        animator.addListener(
-            new AnimatorListenerAdapter() {
-              @Override
-              public void onAnimationStart(Animator animator) {
-                selectedPosition = position;
-              }
-
-              @Override
-              public void onAnimationEnd(Animator animator) {
-                selectedPosition = position;
-              }
-            });
         animator.start();
       } else {
         // Reuse the existing animator. Updating the listener only modifies the target positions.