ChipGroup single selection

Question

How can I force a ChipGroup to act like a RadioGroup as in having at least one selected item always? Setting setSingleSelection(true) also adds the possibility to have nothing selected if you click twice on a Chip.

Answer 1

To prevent all chips from being deselected you can use the method setSelectionRequired:

chipGroup.setSelectionRequired(true)

You can also define it in the layout using the app:selectionRequired attribute:

<com.google.android.material.chip.ChipGroup
    app:singleSelection="true"
    app:selectionRequired="true"
    app:checkedChip="@id/..."
    ..>

Note: This requires a minimum of version 1.2.0

Answer 2

EDIT

With version 1.2.0-alpha02 the old hacky solution is no longer required!

Either use the attribute app:selectionRequired="true"

<com.google.android.material.chip.ChipGroup
            android:id="@+id/group"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:selectionRequired="true"
            app:singleSelection="true">

  (...)
</com.google.android.material.chip.ChipGroup>

Or in code

// Kotlin
group.isSelectionRequired = true

// Java
group.setSelectionRequired(true);

---

For older versions 👇

There are two steps to achieve this

Step 1

We have this support built-in, just make sure to add app:singleSelection="true" to your ChipGroup, for example:

XML

<com.google.android.material.chip.ChipGroup
            android:id="@+id/group"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:singleSelection="true">

        <com.google.android.material.chip.Chip
                android:id="@+id/option_1"
                style="@style/Widget.MaterialComponents.Chip.Choice"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Option 1" />

        <com.google.android.material.chip.Chip
                android:id="@+id/option_2"
                style="@style/Widget.MaterialComponents.Chip.Choice"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Option 2" />
</com.google.android.material.chip.ChipGroup>

Code

// Kotlin
group.isSingleSelection = true

// Java
group.setSingleSelection(true);

Step 2

Now to support a radio group like functionality:

var lastCheckedId = View.NO_ID
chipGroup.setOnCheckedChangeListener { group, checkedId ->
    if(checkedId == View.NO_ID) {
        // User tried to uncheck, make sure to keep the chip checked          
        group.check(lastCheckedId)
        return@setOnCheckedChangeListener
    }
    lastCheckedId = checkedId

    // New selection happened, do your logic here.
    (...)

}

From the docs:

ChipGroup also supports a multiple-exclusion scope for a set of chips. When you set the app:singleSelection attribute, checking one chip that belongs to a chip group unchecks any previously checked chip within the same group. The behavior mirrors that of RadioGroup.

Answer 3

A solution would be to preset a clicked chip and then toggling the clickable property of the chips:

chipGroup.setOnCheckedChangeListener((chipGroup, id) -> {
    Chip chip = ((Chip) chipGroup.getChildAt(chipGroup.getCheckedChipId()));
    if (chip != null) {
        for (int i = 0; i < chipGroup.getChildCount(); ++i) {
            chipGroup.getChildAt(i).setClickable(true);
        }
        chip.setClickable(false);
    }
});