[DatePicker] expand the touch area of a month's days

PiperOrigin-RevId: 437775591

Author: veganafro

lib/java/com/google/android/material/datepicker/MonthAdapter.java

@@ -17,8 +17,12 @@
 
 import com.google.android.material.R;
 
+import static java.lang.Math.max;
+
 import android.content.Context;
+import android.graphics.Rect;
 import android.view.LayoutInflater;
+import android.view.TouchDelegate;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.BaseAdapter;
@@ -48,6 +52,8 @@ class MonthAdapter extends BaseAdapter {
           + UtcDates.getUtcCalendar().getMaximum(Calendar.DAY_OF_WEEK)
           - 1;
 
+  private static final int MIN_TOUCH_TARGET_SIZE_DP = 48;
+
   final Month month;
   /**
    * The {@link DateSelector} dictating the draw behavior of {@link #getView(int, View, ViewGroup)}.
@@ -107,13 +113,13 @@ public int getCount() {
 
   @NonNull
   @Override
-  public TextView getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
+  public TextView getView(
+      int position, @Nullable View convertView, @NonNull final ViewGroup parent) {
     initializeStyles(parent.getContext());
-    TextView day = (TextView) convertView;
-    if (convertView == null) {
-      LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
-      day = (TextView) layoutInflater.inflate(R.layout.mtrl_calendar_day, parent, false);
-    }
+    final TextView day = convertView == null
+        ? (TextView) LayoutInflater.from(parent.getContext()).inflate(
+            R.layout.mtrl_calendar_day, parent, false)
+        : (TextView) convertView;
     int offsetPosition = position - firstPositionInMonth();
     if (offsetPosition < 0 || offsetPosition >= month.daysInMonth) {
       day.setVisibility(View.GONE);
@@ -139,6 +145,22 @@ public TextView getView(int position, @Nullable View convertView, @NonNull ViewG
       return day;
     }
     updateSelectedState(day, date);
+    parent.post(new Runnable() {
+      @Override
+      public void run() {
+        final Rect delegateArea = new Rect();
+        day.getHitRect(delegateArea);
+
+        int dayTouchTargetDeltaVertical = max(0, MIN_TOUCH_TARGET_SIZE_DP - day.getHeight());
+        int dayTouchTargetDeltaHorizontal = max(0, MIN_TOUCH_TARGET_SIZE_DP - day.getWidth());
+
+        delegateArea.top -= dayTouchTargetDeltaVertical;
+        delegateArea.right += dayTouchTargetDeltaHorizontal;
+        delegateArea.bottom += dayTouchTargetDeltaVertical;
+        delegateArea.left -= dayTouchTargetDeltaHorizontal;
+        parent.setTouchDelegate(new TouchDelegate(delegateArea, day));
+      }
+    });
     return day;
   }