自定义控件，实现加载图片时透明变换

/**
 *知我者为我心忧，不知我者谓我何求！
 *linwoain@outlook.com
 *作者 linwoain
 *日期 2014/11/7 9:17
 */
package com.linwoain.TestAndroid.fragment;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;
import android.widget.ImageView;
import com.linwoain.TestAndroid.R;
import java.util.Timer;
import java.util.TimerTask;
/**
 * 自定义控件，实现
 * @author linwoain
 * @version 2014/11/7 9:17
 */
public class AlphaImageView extends ImageView {
    private static final int SPEED = 300;//每隔多少毫秒透明度改变一次
    private int alphaDelta = 0;//图像透明度每次改变的大小
    //记录图片当前的透明度
    private int curAlpha = 0;
    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (msg.what == 0x123) {
                curAlpha += alphaDelta;
                if (curAlpha > 255) {
                    curAlpha = 255;
                    AlphaImageView.this.setAlpha(curAlpha);
                }
            }
        }
    };
    public AlphaImageView(Context context) {
        this(context, null);
    }
    public AlphaImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.AlphaImageView);
        int duration = typedArray.getInt(R.styleable.AlphaImageView_duration, 0);//默认不透明
        alphaDelta = 255 * SPEED / duration;
        typedArray.recycle();
    }
    @Override
    protected void onDraw(Canvas canvas) {
        this.setAlpha(curAlpha);
        super.onDraw(canvas);
        final Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                Message message = new Message();
                message.what = 0x123;
                if (curAlpha >= 255) {
                    timer.cancel();
                } else {
                    handler.sendMessage(message);
                }
            }
        }, 0, SPEED);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="duration"></attr>
    <declare-styleable name="AlphaImageView">
        <attr name="duration"></attr>
    </declare-styleable>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="AlphaImageView">
        <attr name="duration" format="integer"></attr>
    </declare-styleable>
</resources>

    <com.linwoain.TestAndroid.fragment.AlphaImageView
            app:duration="6000"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/gif"/>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" ①
              xmlns:app="http://schemas.android.com/apk/res/com.linwoain.TestAndroid" ② 
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
            >