MainActivity的内容:
import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
    private int[] pics = new int[] {
            R.drawable.p1, R.drawable.p1, R.drawable.p1, R.drawable.p1,
            R.drawable.p1, R.drawable.p1, R.drawable.p1, R.drawable.p1
};
    private GridView grid_view;
    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        grid_view = (GridView) findViewById(R.id.grid_view);
        MyAdapter adapter = new MyAdapter(this);
        grid_view.setAdapter(adapter);
    }
    static class ViewHolder {
        public ImageView img;
    }
    public class MyAdapter extends BaseAdapter {
        private LayoutInflater inflater = null;
        public MyAdapter(Context context) {
            this.inflater = LayoutInflater.from(context);
        }
        @Override
public int getCount() {
            return pics.length;
        }

        @Override
public Object getItem(int position) {
            return pics[position];
        }

        @Override
public long getItemId(int position) {
            return position;
        }

        @Override
public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder = null;
            if(convertView == null) {
                holder = new ViewHolder();
                convertView = inflater.inflate(R.layout.item,null);
                holder.img = (ImageView) convertView.findViewById(R.id.img);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }
            holder.img.setImageResource( pics[position]);
            holder.img.setScaleType(ImageView.ScaleType.FIT_XY);
            holder.img.setLayoutParams(new GridView.LayoutParams(300,200));
            return convertView;
        }
    }
}
item:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
    <ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="12sp"
android:id="@+id/img"/>
</LinearLayout>
activity_main:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
    <GridView
android:id="@+id/grid_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:numColumns="3"
android:padding="12sp" />
</LinearLayout>
为什么我用相似的方法写ListView的适配器可以，而写GridView的有错误（在模拟器上不能运行），望大神帮我看一看！！谢谢！