Allow ListView item highlighting programatically (#2094)

* Refactor & implement highlighting of selected item (both via blocks and listeners)
* Fix NPE with regards to last seen view in ListView selection

appinventor/components/src/com/google/appinventor/components/runtime/ListView.java

@@ -7,7 +7,10 @@
 package com.google.appinventor.components.runtime;
 
 import android.graphics.Color;
+import android.graphics.drawable.ColorDrawable;
+import android.graphics.drawable.Drawable;
 import android.graphics.drawable.GradientDrawable;
+import android.graphics.drawable.StateListDrawable;
 import android.text.Editable;
 import android.text.Spannable;
 import android.text.SpannableString;
@@ -16,6 +19,7 @@ import android.text.style.AbsoluteSizeSpan;
 import android.text.style.ForegroundColorSpan;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.AbsListView;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
 import android.widget.EditText;
@@ -57,7 +61,8 @@ import com.google.appinventor.components.runtime.util.YailList;
     nonVisible = false,
     iconName = "images/listView.png")
 @SimpleObject
-public final class ListView extends AndroidViewComponent implements AdapterView.OnItemClickListener {
+public final class ListView extends AndroidViewComponent implements AdapterView.OnItemClickListener,
+    AdapterView.OnItemSelectedListener {
 
   private static final String LOG_TAG = "ListView";
 
@@ -85,6 +90,10 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
 
   private int selectionColor;
   private static final int DEFAULT_SELECTION_COLOR = Component.COLOR_LTGRAY;
+  private static final Drawable UNSELECTED_DRAWABLE = new ColorDrawable(Color.TRANSPARENT);
+
+  private Drawable selectionDrawable;
+  private View lastSelected;
 
   private int textSize;
   private static final int DEFAULT_TEXT_SIZE = 22;
@@ -101,8 +110,10 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
     SelectionIndex(0);
     view = new android.widget.ListView(container.$context());
     view.setOnItemClickListener(this);
+    view.setOnItemSelectedListener(this);
     view.setChoiceMode(android.widget.ListView.CHOICE_MODE_SINGLE);
     view.setScrollingCacheEnabled(false);
+    view.setSelector(new StateListDrawable()); // Set to empty selector to prevent issues with dynamic highlighting
     listViewLayout = new LinearLayout(container.$context());
     listViewLayout.setOrientation(LinearLayout.VERTICAL);
 
@@ -337,6 +348,8 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
     selectionIndex = ElementsUtil.selectionIndex(index, items);
     // Now, we need to change Selection to correspond to SelectionIndex.
     selection = ElementsUtil.setSelectionFromIndex(index, items);
+
+    updateSelectionIndex();
   }
 
   /**
@@ -361,6 +374,36 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
     selection = value;
     // Now, we need to change SelectionIndex to correspond to Selection.
     selectionIndex = ElementsUtil.setSelectedIndexFromValue(value, items);
+
+    updateSelectionIndex();
+  }
+
+  /**
+   * Action to take after updating selection index.
+   * Handles highlighting the newly updated item.
+   */
+  private void updateSelectionIndex() {
+    if (selectionIndex > 0) {
+      // Store last active view to refocus it later
+      View previousView = Form.getActiveForm().getCurrentFocus();
+
+      // We need to request focus from the ListView in order for the
+      // drawable changes to apply to the active item view.
+      view.requestFocusFromTouch();
+
+      // Set selection to 0-based index (which will in turn call
+      // the necessary listener)
+      view.setSelection(selectionIndex - 1);
+
+      // Re-focus last view
+      if (previousView != null) {
+        previousView.requestFocus();
+      }
+    } else if (lastSelected != null) {
+        // Un-set selected drawable from the last selected item
+        lastSelected.setBackgroundDrawable(UNSELECTED_DRAWABLE);
+        lastSelected = null;
+      }
   }
 
   /**
@@ -373,9 +416,35 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
     this.selection = item.toString();
     this.selectionIndex = adapterCopy.getPosition(item) + 1; // AI lists are 1-based
 
+    // Un-set drawable from previous last selected item
+    if (lastSelected != null) {
+      lastSelected.setBackgroundDrawable(UNSELECTED_DRAWABLE);
+    }
+
+    // Set selected drawable to current view
+    view.setBackgroundDrawable(selectionDrawable);
+
+    // Update last selected
+    lastSelected = view;
+
     AfterPicking();
   }
 
+  /**
+   * Simple event to raise when the component is selected. Implementation of
+   * AdapterView.OnItemSelectedListener.
+   */
+  @Override
+  public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
+    // Defer to item click
+    onItemClick(adapterView, view, i, l);
+  }
+
+  @Override
+  public void onNothingSelected(AdapterView<?> adapterView) {
+
+  }
+
   /**
    * Simple event to be raised after the an element has been chosen in the list.
    * The selected element is available in the {@link #Selection(String)} property.
@@ -466,9 +535,8 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
   @SimpleProperty
   public void SelectionColor(int argb) {
     selectionColor = argb;
-    view.setSelector(new GradientDrawable(
-      GradientDrawable.Orientation.TOP_BOTTOM, new int[]{argb, argb}
-    ));
+    this.selectionDrawable = new GradientDrawable(
+      GradientDrawable.Orientation.TOP_BOTTOM, new int[]{argb, argb});
   }
 
   /**
@@ -533,5 +601,4 @@ public final class ListView extends AndroidViewComponent implements AdapterView.
         textSize = fontSize;
       setAdapterData();
   }
-
 }