Add selection required option to ChipGroup

Resolves #651

PiperOrigin-RevId: 281274404

Author: ymarian

lib/java/com/google/android/material/chip/ChipGroup.java

@@ -38,7 +38,6 @@
 import java.util.ArrayList;
 import java.util.List;
 
-
 /**
  * A ChipGroup is used to hold multiple {@link Chip}s. By default, the chips are reflowed across
  * multiple lines. Set the {@link R.attr#singleLine app:singleLine} attribute to constrain the chips
@@ -88,6 +87,7 @@ public LayoutParams(MarginLayoutParams source) {
   @Dimension private int chipSpacingHorizontal;
   @Dimension private int chipSpacingVertical;
   private boolean singleSelection;
+  private boolean selectionRequired;
 
   @Nullable private OnCheckedChangeListener onCheckedChangeListener;
 
@@ -126,6 +126,7 @@ public ChipGroup(Context context, AttributeSet attrs, int defStyleAttr) {
         a.getDimensionPixelOffset(R.styleable.ChipGroup_chipSpacingVertical, chipSpacing));
     setSingleLine(a.getBoolean(R.styleable.ChipGroup_singleLine, false));
     setSingleSelection(a.getBoolean(R.styleable.ChipGroup_singleSelection, false));
+    setSelectionRequired(a.getBoolean(R.styleable.ChipGroup_selectionRequired, false));
     int checkedChip = a.getResourceId(R.styleable.ChipGroup_checkedChip, View.NO_ID);
     if (checkedChip != View.NO_ID) {
       checkedId = checkedChip;
@@ -442,6 +443,27 @@ public void setSingleSelection(@BoolRes int id) {
     setSingleSelection(getResources().getBoolean(id));
   }
 
+  /**
+   * Sets whether we prevent all child chips from being deselected.
+   *
+   * @attr ref R.styleable#ChipGroup_selectionRequired
+   * @see #setSingleSelection(boolean)
+   */
+  public void setSelectionRequired(boolean selectionRequired) {
+    this.selectionRequired = selectionRequired;
+  }
+
+  /**
+   * Returns whether we prevent all child chips from being deselected.
+   *
+   * @attr ref R.styleable#ChipGroup_selectionRequired
+   * @see #setSingleSelection(boolean)
+   * @see #setSelectionRequired(boolean)
+   */
+  public boolean isSelectionRequired() {
+    return selectionRequired;
+  }
+
   private class CheckedStateTracker implements CompoundButton.OnCheckedChangeListener {
     @Override
     public void onCheckedChanged(@NonNull CompoundButton buttonView, boolean isChecked) {
@@ -450,17 +472,22 @@ public void onCheckedChanged(@NonNull CompoundButton buttonView, boolean isCheck
         return;
       }
 
+      List<Integer> checkedChipIds = getCheckedChipIds();
+      if (checkedChipIds.isEmpty() && selectionRequired) {
+        setCheckedStateForView(buttonView.getId(), true);
+        setCheckedId(buttonView.getId());
+        return;
+      }
+
       int id = buttonView.getId();
 
       if (isChecked) {
         if (checkedId != View.NO_ID && checkedId != id && singleSelection) {
           setCheckedStateForView(checkedId, false);
         }
         setCheckedId(id);
-      } else {
-        if (checkedId == id) {
-          setCheckedId(View.NO_ID);
-        }
+      } else if (checkedId == id) {
+        setCheckedId(View.NO_ID);
       }
     }
   }

lib/java/com/google/android/material/chip/res/values/attrs.xml

@@ -150,6 +150,9 @@
     <!-- Whether only a single chip in this group is allowed to be checked at any time. By default,
          this is false and multiple chips in this group are allowed to be checked at once. -->
     <attr name="singleSelection"/>
+    <!-- Whether we prevent all child chips from being deselected.
+         It's false by default. -->
+    <attr name="selectionRequired"/>
     <!-- The id of the child chip that should be checked by default within this chip group. -->
     <attr name="checkedChip" format="reference"/>
 

lib/java/com/google/android/material/resources/res/values/attrs.xml

@@ -19,6 +19,7 @@
   <attr name="checkedIcon" format="reference" />
   <attr name="minTouchTargetSize" format="dimension"/>
   <attr name="singleSelection" format="boolean"/>
+  <attr name="selectionRequired" format="boolean"/>
   <attr name="strokeColor" format="color"/>
   <attr name="strokeWidth" format="dimension"/>
   <attr name="ensureMinTouchTargetSize" format="boolean"/>

lib/javatests/com/google/android/material/chip/ChipGroupTest.java

@@ -27,11 +27,9 @@
 import org.junit.runner.RunWith;
 import org.robolectric.Robolectric;
 import org.robolectric.RobolectricTestRunner;
-import org.robolectric.annotation.internal.DoNotInstrument;
 
 /** Tests for {@link com.google.android.material.chip.ChipGroup}. */
 @RunWith(RobolectricTestRunner.class)
-@DoNotInstrument
 public class ChipGroupTest {
 
   private static final int CHIP_GROUP_SPACING = 4;
@@ -86,4 +84,45 @@ public void testSingleCheckedChip() {
     int checkedId2 = chipgroup.getCheckedChipId();
     assertThat(checkedId1).isEqualTo(checkedId2);
   }
+
+  @Test
+  public void singleSelection_withSelectionRequired_doesNotUnSelect() {
+    chipgroup.setSelectionRequired(true);
+    chipgroup.setSingleSelection(true);
+
+    View chip = chipgroup.getChildAt(0);
+    chip.performClick();
+    chip.performClick();
+
+    assertThat(((Chip) chip).isChecked()).isTrue();
+  }
+
+  @Test
+  public void singleSelection_withoutSelectionRequired_unSelects() {
+    chipgroup.setSingleSelection(true);
+    chipgroup.setSelectionRequired(false);
+
+    View chip = chipgroup.getChildAt(0);
+    chip.performClick();
+    chip.performClick();
+
+    assertThat(((Chip) chip).isChecked()).isFalse();
+  }
+
+  @Test
+  public void multiSelection_withSelectionRequired_unSelectsIfTwo() {
+    chipgroup.setSingleSelection(false);
+    chipgroup.setSelectionRequired(true);
+
+    View first = chipgroup.getChildAt(0);
+    View second = chipgroup.getChildAt(1);
+    first.performClick();
+
+    second.performClick();
+    second.performClick();
+
+    // first button is selected
+    assertThat(((Chip) first).isChecked()).isTrue();
+    assertThat(((Chip) second).isChecked()).isFalse();
+  }
 }