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      1 /*
      2  * Copyright (C) 2006 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.view.animation;
     18 
     19 import android.content.Context;
     20 import android.content.res.TypedArray;
     21 import android.util.AttributeSet;
     22 
     23 /**
     24  * An animation that controls the alpha level of an object.
     25  * Useful for fading things in and out. This animation ends up
     26  * changing the alpha property of a {@link Transformation}
     27  *
     28  */
     29 public class AlphaAnimation extends Animation {
     30     private float mFromAlpha;
     31     private float mToAlpha;
     32 
     33     /**
     34      * Constructor used when an AlphaAnimation is loaded from a resource.
     35      *
     36      * @param context Application context to use
     37      * @param attrs Attribute set from which to read values
     38      */
     39     public AlphaAnimation(Context context, AttributeSet attrs) {
     40         super(context, attrs);
     41 
     42         TypedArray a =
     43             context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.AlphaAnimation);
     44 
     45         mFromAlpha = a.getFloat(com.android.internal.R.styleable.AlphaAnimation_fromAlpha, 1.0f);
     46         mToAlpha = a.getFloat(com.android.internal.R.styleable.AlphaAnimation_toAlpha, 1.0f);
     47 
     48         a.recycle();
     49     }
     50 
     51     /**
     52      * Constructor to use when building an AlphaAnimation from code
     53      *
     54      * @param fromAlpha Starting alpha value for the animation, where 1.0 means
     55      *        fully opaque and 0.0 means fully transparent.
     56      * @param toAlpha Ending alpha value for the animation.
     57      */
     58     public AlphaAnimation(float fromAlpha, float toAlpha) {
     59         mFromAlpha = fromAlpha;
     60         mToAlpha = toAlpha;
     61     }
     62 
     63     /**
     64      * Changes the alpha property of the supplied {@link Transformation}
     65      */
     66     @Override
     67     protected void applyTransformation(float interpolatedTime, Transformation t) {
     68         final float alpha = mFromAlpha;
     69         t.setAlpha(alpha + ((mToAlpha - alpha) * interpolatedTime));
     70     }
     71 
     72     @Override
     73     public boolean willChangeTransformationMatrix() {
     74         return false;
     75     }
     76 
     77     @Override
     78     public boolean willChangeBounds() {
     79         return false;
     80     }
     81 
     82     /**
     83      * @hide
     84      */
     85     @Override
     86     public boolean hasAlpha() {
     87         return true;
     88     }
     89 }
     90