简谈GridView

GridView是网格形势布局的一种View，要实现它就要设置它的Adapter，GridView的Adapter都是ListAdapter的子类或者间接子类.Adapter其实是起桥接作用的，它把你想要显示的资源放入你指定的组件里面，然后自动地添加进GridView里面。

ListAdapter的父子关系:

现在的例子是：将数张图片资源放进项目的res/drawable里面，将这些图片显示在GridView中，当点击图片的时候会以Toast提醒用户所选图片的ID号.

程序运行结果：

main.xml:

<?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" >

    <GridView
        android:id="@+id/myphoto"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:columnWidth="90dp"
        android:horizontalSpacing="10dp"
        android:numColumns="3"
        android:verticalSpacing="10dp" >
    </GridView>

</LinearLayout>

GridViewDemo.java:

public class GridViewDemo extends Activity
{
	private GridView gridView;

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

		gridView = (GridView) findViewById(R.id.myphoto);
		gridView.setAdapter(new ImageAdapter(this));

		gridView.setOnItemClickListener(new OnItemClickListener()
		{
			public void onItemClick(AdapterView<?> parent, View view, int position, long id)
			{
				Toast.makeText(GridViewDemo.this, "当前被点击的图片ID是:" + position, Toast.LENGTH_SHORT).show();
			}
		});
	}

	/**
	 * 自定义的适配器,用来桥接GridView和需要显示的数据
	 */
	class ImageAdapter extends BaseAdapter
	{
		private Context context;
		// 图片对应的资源ID
		private List<Integer> imgID;

		ImageAdapter(Context context)
		{
			this.context = context;
			this.imgID = new ArrayList<Integer>();
			// 利用反射机制得到R.drawable类里面的属性，即为图片资源ID
			Field[] field = R.drawable.class.getDeclaredFields();
			for (Field myfield : field)
			{
				// 除去程序启动图标
				if (!"icon_lunch".equals(myfield.getName()))
					try
					{
						// 得到属性值
						Integer index = myfield.getInt(R.drawable.class);
						imgID.add(index);
					}
					catch (Exception e)
					{
						e.printStackTrace();
					}
			}

			// imgID.add(R.drawable.sample_0);
			// imgID.add(R.drawable.sample_1);
			// imgID.add(R.drawable.sample_10);
			// imgID.add(R.drawable.sample_11);
			// imgID.add(R.drawable.sample_12);
			// imgID.add(R.drawable.sample_2);
			// imgID.add(R.drawable.sample_3);
		}

		public int getCount()
		{
			return imgID.size();
		}

		public Object getItem(int position)
		{
			// TODO Auto-generated method stub
			return null;
		}

		public long getItemId(int position)
		{
			// TODO Auto-generated method stub
			return position;
		}

		/**
		 * 将对应的资源封装到你定义的组件里,这里是ImageView
		 */
		public View getView(int position, View convertView, ViewGroup parent)
		{
			ImageView imgView;
			// 首先判断是否已经存在ImageView，防止重复加载
			if (null == convertView)
			{
				imgView = new ImageView(context);
				imgView.setScaleType(ImageView.ScaleType.CENTER_CROP);
				imgView.setLayoutParams(new GridView.LayoutParams(100, 100));
				imgView.setPadding(8, 8, 8, 8);
			}
			else
				imgView = (ImageView) convertView;
			imgView.setImageResource(imgID.get(position));
			return imgView;
		}
	}
}

关键就在于实现自己的Adapter