Android getBackground().setAlpha遇到問題解決辦法

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent" >
  <TextView
    android:id="@+id/text1"
    android:layout_width="match_parent"
    android:layout_height="60dp" 
    android:background="@color/text_orange"
    />
  <TextView
    android:id="@+id/text2"
    android:layout_width="match_parent"
    android:layout_height="60dp"
    android:background="@color/text_orange"
    />
</LinearLayout>

/**
 * Make this drawable mutable. This operation cannot be reversed. A mutable
 * drawable is guaranteed to not share its state with any other drawable.
 * This is especially useful when you need to modify properties of drawables
 * loaded from resources. By default, all drawables instances loaded from
 * the same resource share a common state; if you modify the state of one
 * instance, all the other instances will receive the same modification.
 *
 * Calling this method on a mutable Drawable will have no effect.
 *
 * @return This drawable.
 * @see ConstantState
 * @see #getConstantState()
 */
public Drawable mutate() {
  return this;
}

text1.getBackground().mutate().setAlpha(255);