main.xml

<?xml version="1.0" encoding="utf-8"?>
<GridView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/gridview"
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent"
    android:columnWidth="90dp"
    android:numColumns="auto_fit"
    android:verticalSpacing="10dp"
    android:horizontalSpacing="10dp"
    android:stretchMode="columnWidth"
    android:gravity="center"
/>

介绍一下里面的某些属性：

android:numColumns=”auto_fit” ，GridView的列数设置为自动

android:columnWidth=”90dp”，每列的宽度，也就是Item的宽度
android:stretchMode=”columnWidth”，缩放与列宽大小同步
android:verticalSpacing=”10dp”，两行之间的边距，
android:horizontalSpacing=”10dp”，两列之间的边距。

  activity:

public class GridviewActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        GridView gridview = (GridView) findViewById(R.id.gridview);
        //主要是重写了BaseAdapter中的getView方法
        gridview.setAdapter(new ImageAdapter(this));
        gridview.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
                Toast.makeText(GridviewActivity.this, "" + position, Toast.LENGTH_SHORT).show();
            }
        });
    }
    class ImageAdapter extends BaseAdapter {
        private Context mContext;

        public ImageAdapter(Context c) {
            mContext = c;
        }
        public int getCount() {//数组的长度
            return mThumbIds.length;
        }
        public Object getItem(int position) {
            return null;
        }
        public long getItemId(int position) {
            return 0;
        }
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView imageView;
            if (convertView == null) {  // 如果不存在就创建一个convertView
                imageView = new ImageView(mContext);
                imageView.setLayoutParams(new GridView.LayoutParams(85, 85));//width,heigth
                imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
                imageView.setPadding(8, 8, 8, 8);//padding
            } else {
                imageView = (ImageView) convertView;
            }

            imageView.setImageResource(mThumbIds[position]);
            return imageView;
        }
        // references to our images
        private Integer[] mThumbIds = {
                R.drawable.sample_2, R.drawable.sample_3,
                R.drawable.sample_4, R.drawable.sample_5,
                R.drawable.sample_6, R.drawable.sample_7,
                R.drawable.sample_0, R.drawable.sample_1,
                R.drawable.sample_2, R.drawable.sample_3,
                R.drawable.sample_4, R.drawable.sample_5,
                R.drawable.sample_6, R.drawable.sample_7,
                R.drawable.sample_0, R.drawable.sample_1,
                R.drawable.sample_2, R.drawable.sample_3,
                R.drawable.sample_4, R.drawable.sample_5,
                R.drawable.sample_6, R.drawable.sample_7
        };
    }
}

 这些代码是文档上的源代码

这里我们重点理解ImageView的属性android:scaleType

android:scaleType是控制图片如何resized/moved来匹对ImageView的size。ImageView.ScaleType / android:scaleType值的意义区别：  
CENTER /center  按图片的原来size居中显示，当图片长/宽超过View的长/宽，则截取图片的居中部分显示  
CENTER_CROP / centerCrop  按比例扩大图片的size居中显示，使得图片长(宽)等于或大于View的长(宽)  
CENTER_INSIDE / centerInside  将图片的内容完整居中显示，通过按比例缩小或原来的size使得图片长/宽等于或小于View的长/宽  
FIT_CENTER / fitCenter  把图片按比例扩大/缩小到View的宽度，居中显示  
FIT_END / fitEnd  
 把图片按比例扩大/缩小到View的宽度，显示在View的下部分位置  
FIT_START / fitStart
  把图片按比例扩大/缩小到View的宽度，显示在View的上部分位置  
FIT_XY / fitXY  把图片
不按比例

这里转载：
http://android.blog.51cto.com/268543/316255