Take CompoundButtons drawables min size into account during measurements (#528)

CompoundButtons such as Checkboxes, when are allowed to shrink (flexShrink = 1f), during the recalculation can end up being shrunk more than what I would consider their "minimum size" since the negative space is calculated for all FlexItems in the shrinkFlexItems() method.

In this PR I try to prevent these components to get completely shrunk by considering the minimum size of their button drawable. In this way, the drawable size will determine the minimum size of the widget unless a minWidth or minHeight are specified by the user.

flexbox/src/androidTest/java/com/google/android/flexbox/FlexboxHelperTest.kt

@@ -17,6 +17,7 @@
 package com.google.android.flexbox
 
 import android.view.View
+import android.widget.CheckBox
 import android.widget.TextView
 import androidx.test.rule.ActivityTestRule
 import androidx.test.runner.AndroidJUnit4
@@ -399,6 +400,74 @@ class FlexboxHelperTest {
         assertThat(view3.measuredWidth, `is`(100))
     }
 
+    @Test
+    @Throws(Throwable::class)
+    fun testDetermineMainSize_directionRow_considerCompoundButtonImplicitMinSizeWhenNotSpecified() {
+        val containerWidth = 500
+        val activity = activityRule.activity
+        val lp1 = FlexboxLayout.LayoutParams(
+                FlexboxLayout.LayoutParams.WRAP_CONTENT,
+                FlexboxLayout.LayoutParams.WRAP_CONTENT)
+        val view1 = CheckBox(activity)
+        view1.layoutParams = lp1
+        val lp2 = FlexboxLayout.LayoutParams(
+                FlexboxLayout.LayoutParams.WRAP_CONTENT,
+                FlexboxLayout.LayoutParams.WRAP_CONTENT)
+        val view2 = TextView(activity)
+        view2.layoutParams = lp2
+        view2.text = LONG_TEXT
+        flexContainer.addView(view1)
+        flexContainer.addView(view2)
+        flexContainer.flexWrap = FlexWrap.NOWRAP
+        val widthMeasureSpec = View.MeasureSpec.makeMeasureSpec(containerWidth, View.MeasureSpec.AT_MOST)
+        val heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(1000, View.MeasureSpec.UNSPECIFIED)
+        val result = FlexboxHelper.FlexLinesResult()
+        flexboxHelper.calculateHorizontalFlexLines(result, widthMeasureSpec, heightMeasureSpec)
+        flexContainer.flexLines = result.mFlexLines
+        flexboxHelper.determineMainSize(widthMeasureSpec, heightMeasureSpec)
+
+        // CompoundButton will use its ButtonDrawable minWidth to determine its size when
+        // no minimum width is set on it.
+        val drawableMinWidth = view1.buttonDrawable!!.minimumWidth
+        val expectedTextWidth = containerWidth - drawableMinWidth
+        assertThat(view1.measuredWidth, `is`(drawableMinWidth))
+        assertThat(view2.measuredWidth, `is`(expectedTextWidth))
+    }
+
+    @Test
+    @Throws(Throwable::class)
+    fun testDetermineMainSize_directionRow_considerCompoundButtonExplicitMinSizeWhenSpecified() {
+        val containerWidth = 500
+        val compoundButtonMinWidth = 150
+        val activity = activityRule.activity
+        val lp1 = FlexboxLayout.LayoutParams(
+                FlexboxLayout.LayoutParams.WRAP_CONTENT,
+                FlexboxLayout.LayoutParams.WRAP_CONTENT)
+        lp1.minWidth = compoundButtonMinWidth
+        val view1 = CheckBox(activity)
+        view1.layoutParams = lp1
+        val lp2 = FlexboxLayout.LayoutParams(
+                FlexboxLayout.LayoutParams.WRAP_CONTENT,
+                FlexboxLayout.LayoutParams.WRAP_CONTENT)
+        val view2 = TextView(activity)
+        view2.layoutParams = lp2
+        view2.text = LONG_TEXT
+        flexContainer.addView(view1)
+        flexContainer.addView(view2)
+        flexContainer.flexWrap = FlexWrap.NOWRAP
+        val widthMeasureSpec = View.MeasureSpec.makeMeasureSpec(containerWidth, View.MeasureSpec.AT_MOST)
+        val heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(1000, View.MeasureSpec.UNSPECIFIED)
+        val result = FlexboxHelper.FlexLinesResult()
+        flexboxHelper.calculateHorizontalFlexLines(result, widthMeasureSpec, heightMeasureSpec)
+        flexContainer.flexLines = result.mFlexLines
+        flexboxHelper.determineMainSize(widthMeasureSpec, heightMeasureSpec)
+
+        // CompoundButton will be measured based on its explicitly specified minWidth.
+        val expectedTextWidth = containerWidth - compoundButtonMinWidth
+        assertThat(view1.measuredWidth, `is`(compoundButtonMinWidth))
+        assertThat(view2.measuredWidth, `is`(expectedTextWidth))
+    }
+
     @Test
     @Throws(Throwable::class)
     fun testDetermineCrossSize_direction_row_alignContent_stretch() {

flexbox/src/main/java/com/google/android/flexbox/FlexboxHelper.java

@@ -19,14 +19,15 @@ package com.google.android.flexbox;
 import static com.google.android.flexbox.FlexContainer.NOT_SET;
 import static com.google.android.flexbox.FlexItem.FLEX_BASIS_PERCENT_DEFAULT;
 import static com.google.android.flexbox.FlexItem.FLEX_GROW_DEFAULT;
-import static com.google.android.flexbox.FlexItem.FLEX_SHRINK_DEFAULT;
 import static com.google.android.flexbox.FlexItem.FLEX_SHRINK_NOT_SET;
 
 import static androidx.recyclerview.widget.RecyclerView.NO_POSITION;
 
+import android.graphics.drawable.Drawable;
 import android.util.SparseIntArray;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.CompoundButton;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -37,6 +38,7 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 import androidx.core.view.MarginLayoutParamsCompat;
+import androidx.core.widget.CompoundButtonCompat;
 
 /**
  * Offers various calculations for Flexbox to use the common logic between the classes such as
@@ -438,6 +440,8 @@ class FlexboxHelper {
                     addFlexLine(flexLines, flexLine, i, sumCrossSize);
                 }
                 continue;
+            } else if (child instanceof CompoundButton) {
+                evaluateMinimumSizeForCompoundButton((CompoundButton) child);
             }
 
             FlexItem flexItem = (FlexItem) child.getLayoutParams();
@@ -628,6 +632,28 @@ class FlexboxHelper {
         result.mChildState = childState;
     }
 
+    /**
+     * Compound buttons (ex. {{@link android.widget.CheckBox}}, {@link android.widget.ToggleButton})
+     * have a button drawable with minimum height and width specified for them.
+     * To align the behavior with CSS Flexbox we want to respect these minimum measurement to avoid
+     * these drawables from being cut off during calculation. When the compound button has a minimum
+     * width or height already specified we will not make any change since we assume those were
+     * voluntarily set by the user.
+     *
+     * @param compoundButton the compound button that need to be evaluated
+     */
+    private void evaluateMinimumSizeForCompoundButton(CompoundButton compoundButton) {
+        FlexItem flexItem = (FlexItem) compoundButton.getLayoutParams();
+        int minWidth = flexItem.getMinWidth();
+        int minHeight = flexItem.getMinHeight();
+
+        Drawable drawable = CompoundButtonCompat.getButtonDrawable(compoundButton);
+        int drawableMinWidth = drawable == null ? 0 : drawable.getMinimumWidth();
+        int drawableMinHeight = drawable == null ? 0 : drawable.getMinimumHeight();
+        flexItem.setMinWidth(minWidth == NOT_SET ? drawableMinWidth : minWidth);
+        flexItem.setMinHeight(minHeight == NOT_SET ? drawableMinHeight : minHeight);
+    }
+
     /**
      * Returns the container's start padding in the main axis. Either start or top.
      *

flexbox/src/main/java/com/google/android/flexbox/FlexboxLayout.java

@@ -1598,12 +1598,12 @@ public class FlexboxLayout extends ViewGroup implements FlexContainer {
         /**
          * @see FlexItem#getMinWidth()
          */
-        private int mMinWidth;
+        private int mMinWidth = NOT_SET;
 
         /**
          * @see FlexItem#getMinHeight()
          */
-        private int mMinHeight;
+        private int mMinHeight = NOT_SET;
 
         /**
          * @see FlexItem#getMaxWidth()
@@ -1636,9 +1636,9 @@ public class FlexboxLayout extends ViewGroup implements FlexContainer {
                     .getFraction(R.styleable.FlexboxLayout_Layout_layout_flexBasisPercent, 1, 1,
                             FLEX_BASIS_PERCENT_DEFAULT);
             mMinWidth = a
-                    .getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_minWidth, 0);
+                    .getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_minWidth, NOT_SET);
             mMinHeight = a
-                    .getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_minHeight, 0);
+                    .getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_minHeight, NOT_SET);
             mMaxWidth = a.getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_maxWidth,
                     MAX_SIZE);
             mMaxHeight = a.getDimensionPixelSize(R.styleable.FlexboxLayout_Layout_layout_maxHeight,