Use DimmableIconPreference for Add user action

Moved DimmableIconPreference from location to the root package since it is
now used in several places.

Add user action now uses DimmableIconPreference. Added a new summary string,
which is displayed when no more users can be added.

Bug: 20892920
Change-Id: I00b00f80ba8933a00a2de85777b9f7e55d03c31b

src/com/android/settings/DimmableIconPreference.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2014 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.settings;
+
+import android.annotation.Nullable;
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.preference.Preference;
+import android.text.TextUtils;
+import android.util.AttributeSet;
+import android.view.View;
+import android.widget.TextView;
+
+/**
+ * A preference item that can dim the icon when it's disabled, either directly or because its parent
+ * is disabled.
+ */
+public class DimmableIconPreference extends Preference {
+    private static final int ICON_ALPHA_ENABLED = 255;
+    private static final int ICON_ALPHA_DISABLED = 102;
+
+    private final CharSequence mContentDescription;
+
+    public DimmableIconPreference(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        mContentDescription = null;
+    }
+
+    public DimmableIconPreference(Context context, @Nullable CharSequence contentDescription) {
+        super(context);
+        mContentDescription = contentDescription;
+    }
+
+    private void dimIcon(boolean dimmed) {
+        Drawable icon = getIcon();
+        if (icon != null) {
+            icon.mutate().setAlpha(dimmed ? ICON_ALPHA_DISABLED : ICON_ALPHA_ENABLED);
+            setIcon(icon);
+        }
+    }
+
+    @Override
+    public void onParentChanged(Preference parent, boolean disableChild) {
+        dimIcon(disableChild);
+        super.onParentChanged(parent, disableChild);
+    }
+
+    @Override
+    public void setEnabled(boolean enabled) {
+        dimIcon(!enabled);
+        super.setEnabled(enabled);
+    }
+
+    @Override
+    protected void onBindView(View view) {
+        super.onBindView(view);
+        if (!TextUtils.isEmpty(mContentDescription)) {
+            final TextView titleView = (TextView) view.findViewById(android.R.id.title);
+            titleView.setContentDescription(mContentDescription);
+        }
+    }
+}