title: Android: why does Checkbox not show empty checkbox for unchecked state?
body: <p>I have checkbox code in a CardView layout file.  The CardView has a white background.  Normally, I think the unchecked Checkbox is a black square.  My layout shows no blank checkbox.  All I see is just the white CardView background (top CardView in the screenshot).  When I click on the right-most area of the CardView where the checkbox code is formatted, a green Checkbox appears (bottom CardView in the screenshot).  What am I missing here?  <a href="https://i.stack.imgur.com/czzuG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/czzuG.png" alt="enter image description here"></a>.</p>
  
  <p>layout file:</p>
  
  <pre><code>&lt;LinearLayout
  
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  android:background="@color/background4main"  &gt;
  
  &lt;android.support.v7.widget.CardView
      xmlns:card_view="http://schemas.android.com/apk/res-auto"
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:id="@+id/singlecard_view1"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      card_view:cardBackgroundColor="@android:color/white"
      card_view:cardCornerRadius="6dp"
      android:orientation="horizontal"
      android:layout_margin="4dp"&gt;
  
      &lt;RelativeLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="?android:selectableItemBackground"  &gt;
  
      &lt;TextView
          android:id="@+id/cardBlankText2"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_alignParentTop="true"
          android:text="todo"
          android:textStyle="bold"
          android:textColor="@android:color/black"
          android:textAppearance="?android:attr/textAppearanceLarge"
          android:textSize="20sp"  /&gt;
  
      &lt;TextView
          android:id="@+id/cardBlankText3"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_below="@+id/cardBlankText2"
          android:text="note1"
          android:textStyle="bold"
          android:textColor="@android:color/black"
          android:textAppearance="?android:attr/textAppearanceLarge"
          android:textSize="20sp"  /&gt;
  
      &lt;CheckBox
          android:id="@+id/chkSelected"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_alignParentRight="true"
          android:layout_alignParentEnd="true"
          android:layout_centerVertical="true"  /&gt;
  
      &lt;/RelativeLayout&gt;
  
  &lt;/android.support.v7.widget.CardView&gt;
  
  &lt;/LinearLayout&gt;
  
  Adapter file:
  ...
  public class ListViewHolder extends RecyclerView.ViewHolder {
  
      TextView cardBlankText2;
      TextView cardBlankText3;
      CheckBox chkSelected;
  
      public ListViewHolder(View itemView) {
          super(itemView);
  
          cardBlankText2 = (TextView)itemView.findViewById(R.id.cardBlankText2);
          cardBlankText3 = (TextView)itemView.findViewById(R.id.cardBlankText3);
          chkSelected = (CheckBox) itemView.findViewById(R.id.chkSelected);
      }
  ...
  @Override
  public void onBindViewHolder(final ListViewHolder holder, final int position) {
  
          holder.cardBlankText2.setText(dbList.get(position).getTodo());
          holder.cardBlankText3.setText(dbList.get(position).getNote1());
          holder.chkSelected.setChecked(dbList.get(position).isSelected());
          holder.chkSelected.setTag(dbList.get(position));
  }
  </code></pre>