Android 程式开发：（十四）显示图像 —— 14.2 ImageSwitcher

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前面的一节，介绍了如何组合使用Gallery和ImageView。但是，有的时候当你在gallery中点击一个图片，你可能不希望一个图片“突然地”在imageview中显示出来。例如，你可能希望给某个图片设置一些切换动画。此时，就需要使用ImageSwitcher和Gallery一起使用。下面展示如何使用ImageSwitcher。

1. 创建一个工程，ImageSwitcher。

2. main.xml中的代码。

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

    < TextView
        android:layout_width = "fill_parent"
        android:layout_height = "wrap_content"
        android:text = "Images of San Francisco" />

    < Gallery
        android:id = "@+id/gallery1"
        android:layout_width = "fill_parent"
        android:layout_height = "wrap_content" />

    < ImageSwitcher
        android:id = "@+id/switcher1"
        android:layout_width = "fill_parent"
        android:layout_height = "fill_parent"
        android:layout_alignParentLeft = "true"
        android:layout_alignParentRight = "true"
        android:layout_alignParentBottom = "true" />

</ LinearLayout >

3. 在res/values文件夹下面新建一个文件，attrs.xml。

4. attrs.xml中的代码。

<? xml version = "1.0" encoding = "utf-8" ?>
< resources >
    < declare-styleable name = "Gallery1" >
        < attr name = "android:galleryItemBackground" />
    </ declare-styleable >
</ resources >

5. 在res/drawable-mdpi中放置一些图片。

6. ImageSwitcherActivity.java中的代码。

public class ImageSwitcherActivity extends Activity implements ViewFactory {
    //---the images to display---
    Integer[] imageIDs = {
            R.drawable.pic1,
            R.drawable.pic2,
            R.drawable.pic3,
            R.drawable.pic4,
            R.drawable.pic5,
            R.drawable.pic6,
            R.drawable.pic7
    };

    private ImageSwitcher imageSwitcher;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout.main);

        imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1);
        imageSwitcher.setFactory( this );

        /*
        imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
                android.R.anim.fade_in));
        imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
                android.R.anim.fade_out));
        */

        imageSwitcher.setInAnimation(AnimationUtils.loadAnimation( this ,
                android.R.anim.slide_in_left));
        imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation( this ,
                android.R.anim.slide_out_right));


        Gallery gallery = (Gallery) findViewById(R.id.gallery1);
        gallery.setAdapter( new ImageAdapter( this ));
        gallery.setOnItemClickListener( new OnItemClickListener()
        {
            public void onItemClick(AdapterView<?> parent,
            View v, int position, long id)
            {
                imageSwitcher.setImageResource(imageIDs[position]);
            }
        });
    }

    public View makeView()
    {
        ImageView imageView = new ImageView( this );
        imageView.setBackgroundColor( 0xFF000000 );
        imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
        imageView.setLayoutParams( new
                ImageSwitcher.LayoutParams(
                        LayoutParams.FILL_PARENT,
                        LayoutParams.FILL_PARENT));
        return imageView;
    }

    public class ImageAdapter extends BaseAdapter
    {
        private Context context;
        private int itemBackground;

        public ImageAdapter(Context c)
        {
            context = c;

            //---setting the style---
            TypedArray a = obtainStyledAttributes(R.styleable.Gallery1);
            itemBackground = a.getResourceId(
                    R.styleable.Gallery1_android_galleryItemBackground, 0 );
            a.recycle();
        }

        //---returns the number of images---
        public int getCount()
        {
            return imageIDs.length;
        }

        //---returns the item---
        public Object getItem( int position)
        {
            return position;
        }

        //---returns the ID of an item---
        public long getItemId( int position)
        {
            return position;
        }

        //---returns an ImageView view---
        public View getView( int position, View convertView, ViewGroup parent)
        {
            ImageView imageView = new ImageView(context);

            imageView.setImageResource(imageIDs[position]);
            imageView.setScaleType(ImageView.ScaleType.FIT_XY);
            imageView.setLayoutParams( new Gallery.LayoutParams( 150 , 120 ));
            imageView.setBackgroundResource(itemBackground);

            return imageView;
        }
    }

}

7. 按F11在模拟器上面调试。会看见Gallery和ImageSwitcher。 

首先，要注意，ImageSwitcherActivity不紧继承了Activity，而且实现了ViewFactory接口。要使用ImageSwitcher，就需要实现ViewFactory接口，这个接口为ImageSwitcher创建视图。只需实现makeView()方法就可以了。

public View makeView()
    {
        ImageView imageView = new ImageView( this );
        imageView.setBackgroundColor( 0xFF000000 );
        imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
        imageView.setLayoutParams( new
                ImageSwitcher.LayoutParams(
                        LayoutParams.FILL_PARENT,
                        LayoutParams.FILL_PARENT));
        return imageView;
    }

这个方法返回一个新的view，这个view将会被添加到ImageSwitcher中，在本例中，此方法返回一个ImageView。

像上一节的例子一样，我们要实现一个ImageAdapter子类，目的是把Gallery和ImageView绑定在一起。

在onCreate()方法中，我们获得ImageSwitcher实例的引用，同时设定了动画animation，这个动画在图片切换的时候被使用。

最后，当一个图片在Gallery中被选择的时候，这个图片就在ImageSwitcher中显示出来的。

private ImageSwitcher imageSwitcher;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super .onCreate(savedInstanceState);
    setContentView(R.layout.main);

    imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1);
    imageSwitcher.setFactory( this );

    /*
    imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
            android.R.anim.fade_in));
    imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
            android.R.anim.fade_out));
    */

    imageSwitcher.setInAnimation(AnimationUtils.loadAnimation( this ,
            android.R.anim.slide_in_left));
    imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation( this ,
            android.R.anim.slide_out_right));


    Gallery gallery = (Gallery) findViewById(R.id.gallery1);
    gallery.setAdapter( new ImageAdapter( this ));
    gallery.setOnItemClickListener( new OnItemClickListener()
    {
        public void onItemClick(AdapterView<?> parent,
        View v, int position, long id)
        {
            imageSwitcher.setImageResource(imageIDs[position]);
        }
    });
}

在这个例子中，通过以下的方法设置动画。

/*
imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
        android.R.anim.fade_in));
imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
        android.R.anim.fade_out));
*/

imageSwitcher.setInAnimation(AnimationUtils.loadAnimation( this ,
        android.R.anim.slide_in_left));
imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation( this ,
        android.R.anim.slide_out_right));