Change SlashDrawable semantics to fix QS crash

SlashDrawable wraps a reference to Drawable in order to store the
intended Drawable and optionally draw a slash over it. As such, it
should probably have similar semantics to Drawable, in that it either
exists or doesn't; if you set SlashImageView's drawable to `null`, you'd
expect that the drawable goes away, not that the SlashDrawable's
contained Drawable goes away but the slash stays.

Test: runtest systemui
Change-Id: I34b92716cc60ba5043ab68ae09954f5a5e97e562
Fixes: 62525439

packages/SystemUI/src/com/android/systemui/qs/tileimpl/SlashImageView.java

@@ -18,12 +18,14 @@ import android.content.Context;
 import android.graphics.drawable.Drawable;
 import android.widget.ImageView;
 
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.systemui.plugins.qs.QSTile.SlashState;
 import com.android.systemui.qs.SlashDrawable;
 
 public class SlashImageView extends ImageView {
 
-    private SlashDrawable mSlash;
+    @VisibleForTesting
+    protected SlashDrawable mSlash;
 
     public SlashImageView(Context context) {
         super(context);
@@ -38,10 +40,13 @@ public class SlashImageView extends ImageView {
 
     @Override
     public void setImageDrawable(Drawable drawable) {
-        if (mSlash != null) {
-            mSlash.setDrawable(drawable);
-        } else {
+        if (drawable == null) {
+            mSlash = null;
+            super.setImageDrawable(null);
+        } else if (mSlash == null) {
             super.setImageDrawable(drawable);
+        } else {
+            mSlash.setDrawable(drawable);
         }
     }
 

packages/SystemUI/tests/src/com/android/systemui/qs/SlashImageViewTest.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.systemui.qs;
+
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.support.test.filters.SmallTest;
+import android.testing.AndroidTestingRunner;
+import android.testing.TestableLooper.RunWithLooper;
+import com.android.systemui.SysuiTestCase;
+import com.android.systemui.plugins.qs.QSTile.SlashState;
+import com.android.systemui.qs.tileimpl.SlashImageView;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+
+@SmallTest
+@RunWith(AndroidTestingRunner.class)
+@RunWithLooper
+public class SlashImageViewTest extends SysuiTestCase {
+    private TestableSlashImageView mSlashView;
+
+    @Test
+    public void testSetSlashStateCreatesSlashDrawable() {
+        SlashState mockState = mock(SlashState.class);
+        Drawable mockDrawable = mock(Drawable.class);
+        mSlashView = new TestableSlashImageView(mContext);
+        assertTrue(mSlashView.getSlashDrawable() == null);
+
+        mSlashView.setImageDrawable(mockDrawable);
+        mSlashView.setState(mockState);
+
+        assertTrue(mSlashView.getSlashDrawable() != null);
+    }
+
+    @Test
+    public void testSetNullDrawableRemovesSlashDrawable() {
+        SlashState mockState = mock(SlashState.class);
+        Drawable mockDrawable = mock(Drawable.class);
+
+        mSlashView = new TestableSlashImageView(mContext);
+        mSlashView.setImageDrawable(mockDrawable);
+        mSlashView.setState(mockState);
+        mSlashView.setImageDrawable(null);
+
+        assertTrue(mSlashView.getSlashDrawable() == null);
+    }
+
+    // Expose getSlashDrawable
+    private static class TestableSlashImageView extends SlashImageView {
+        TestableSlashImageView(Context c) {
+            super(c);
+        }
+
+        private SlashDrawable getSlashDrawable() {
+            return mSlash;
+        }
+    }
+}