Material Button Toggle Group single selection

Question

How can I force a MaterialButtonToggleGroup 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 Button in the group.

Here is my code:

<com.google.android.material.button.MaterialButtonToggleGroup
            android:id="@id/BottomSheetDialog_fromFragmentBottomSheetSort_Sort_ToggleButtonGroup"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:singleSelection="true"
            app:checkedButton="@+id/BottomSheetDialog_fromFragmentBottomSheetSort_Sort_ToggleButtonGroup_Ascending">

        <com.google.android.material.button.MaterialButton
                android:id="@id/BottomSheetDialog_fromFragmentBottomSheetSort_Sort_ToggleButtonGroup_Ascending"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/Fragment_BottomSheetDialog_Sort_ToggleButton_Ascending"
                app:backgroundTint="@color/custom_button_background_states"
                style="@style/Widget.MaterialComponents.Button.OutlinedButton"/>

        <com.google.android.material.button.MaterialButton
                android:id="@id/BottomSheetDialog_fromFragmentBottomSheetSort_Sort_ToggleButtonGroup_Descending"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/Fragment_BottomSheetDialog_Sort_ToggleButton_Descending"
                app:backgroundTint="@color/custom_button_background_states"
                style="@style/Widget.MaterialComponents.Button.OutlinedButton"/>
    </com.google.android.material.button.MaterialButtonToggleGroup>

As you can see, even while using app:singleSelection="true" if i click on an already checked button, it unchecks it leaving no button checked in the group.

Answer 1

从1.2.0-alpha03 开始​​，您可以简单地使用该selectionRequired选项：

<com.google.android.material.button.MaterialButtonToggleGroup
    android:id="@+id/toggle_button_group"
    app:singleSelection="true"
    app:selectionRequired="true">

</com.google.android.material.button.MaterialButtonToggleGroup>

Answer 2

现在您可以使用该app:selectionRequired属性来实现它。
就像是：

    <com.google.android.material.button.MaterialButtonToggleGroup
        app:singleSelection="true"
        app:selectionRequired="true"
        app:checkedButton="@id/..."
        ..>

您也可以以编程方式使用该方法setSelectionRequired：

buttonGroup.setSelectionRequired(true);

请注意，此属性至少需要1.2.0-alpha03版本

Answer 3

重写类的toggle()方法MaterialButton并使用它代替MaterialButton

import android.content.Context
import android.util.AttributeSet
import com.google.android.material.button.MaterialButton

class CustomMaterialToggleButton : MaterialButton {

    constructor(context: Context) : super(context)

    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)

    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)

    override fun toggle() {
        if (!isChecked) {
            super.toggle()
        }
    }
}

这将确保未选中单个选择中已选中的按钮。