6.1.6 Gallery结合案例详解
Gallery（相册）控件是个很不错的图片查看控件，屏幕中有一个图片列表，Gallery类的继承关系如下：
java.lang.Object
? android.view.View
? android.view.ViewGroup
? android.widget.AdapterView<T extends android.widget.Adapter>
? android.widget.AbsSpinner
? android.widget.Gallery
这个Gallery案例，可以用手滑动Gallery，当用户点击某个图片弹出一个Toast，如6-11图：
6-11 Gallery控件使用效果图
程序代码请参考代码清单6-9：
【代码清单6-9】chapter6_5/src/com/work/GalleryActivity.java
public class GalleryActivity extends Activity {@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Gallery g = (Gallery) findViewById(R.id.gallery); g.setAdapter(new ImageAdapter(this)); g.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView parent, View v, int position, long id) { Toast.makeText(GalleryActivity.this, "" + position, Toast.LENGTH_SHORT).show(); } }); registerForContextMenu(g); } @Override public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) { menu.add(R.string.gallerytext); } @Override public boolean onContextItemSelected(MenuItem item) { AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo(); Toast.makeText(this, "Longpress: " + info.position, Toast.LENGTH_SHORT).show(); return true; } public class ImageAdapter extends BaseAdapter { int mGalleryItemBackground; public ImageAdapter(Context c) { mContext = c; TypedArray a = obtainStyledAttributes(R.styleable.Gallery1); mGalleryItemBackground = a.getResourceId( R.styleable.Gallery1_android_galleryItemBackground, 0); a.recycle(); } public int getCount() { return mImageIds.length; } public Object getItem(int position) { return position; } public long getItemId(int position) { return position; } public View getView(int position, View convertView, ViewGroup parent) { ImageView imageView;imageView = new ImageView(mContext);imageView.setImageResource(mImageIds[position]);imageView.setScaleType(ImageView.ScaleType.FIT_XY);imageView.setLayoutParams(new Gallery.LayoutParams(136, 88));imageView.setBackgroundResource(mGalleryItemBackground);return imageView; } private Context mContext; private Integer[] mImageIds = { R.drawable.beijing, R.drawable.changsha, R.drawable.chengdu, R.drawable.chongqing, R.drawable.haerbing, R.drawable.jinan, R.drawable.jiujiang, R.drawable.kunming, R.drawable.nanjing }; }}代码的关键的地方是实现BaseAdapter适配器类——ImageAdapter，其中关键是getView()实现。在convertView为null时候实例化控件，imageView.setLayoutParams(new GridView.LayoutParams(136, 88)是设置一个单元格中图片的大小是136×88像素。imageView.setScaleType(ImageView.ScaleType.FIT_XY) 缩放图片使用FILL方式。imageView.setImageResource(mImageIds[position])为图片控件设置图片。
在布局文件/chapter6_5/res/layout/main.xml中添加Gallery控件：
<?xml version="1.0" encoding="utf-8"?><Gallery xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/gallery"android:layout_width="match_parent"android:layout_height="wrap_content"/>
本例中设置图片的背景样式是边框样式，如图6-12。
图6-12 图片背景样式
imageView.setBackgroundResource(mGalleryItemBackground)语句就是设定样式的，成员变量mGalleryItemBackground是在ImageAdapter的构造方法中初始化的。
public ImageAdapter(Context c) {mContext = c;TypedArray a = obtainStyledAttributes(R.styleable.Gallery1);mGalleryItemBackground = a.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 0);a.recycle();}mGalleryItemBackground是与galleryItemBackground背景资源绑定的id值，这个id对应的galleryItemBackground属性就是设定带有边框的背景样式。
此外还要在chapter6_5/res/values/目录下面创建一个attrs.xml文件：
<?xml version="1.0" encoding="utf-8"?><resources> <declare-styleable name="Gallery1"> <attr name="android:galleryItemBackground" /> </declare-styleable></resources>
这是一个自定义控件属性的xml文件。但是在Android1.0时候没有这么麻烦，而是如下方式实现：
public ImageAdapter(Context c) { mContext = c; TypedArray a = obtainStyledAttributes(android.R.styleable.Theme); mGalleryItemBackground = a.getResourceId( android.R.styleable.Theme_galleryItemBackground, 0); a.recycle();}android.R.styleable.Theme_galleryItemBackground 属性在Android1.0是可以访问的，而在Android1.0之后就不能访问了，而要通过本例的方式获得galleryItemBackground的id值。
出自《Android开发案例驱动教程》