6.1.6 Gallery组合案例详解

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》

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