如何在GridView中对齐ImageView

Question

我已经为我的GridView槽Java代码创建了一个BaseAdapter 我希望Gridview中的图像显示如下：

但我目前的代码使图像显示如下：

调整图像大小的代码是：

public class objectAdapter extends BaseAdapter {
private Context context;
private int[] image_id = {R.drawable.banana, R.drawable.kiwi, R.drawable.oatmeal, R.drawable.coconut};
String[] names = {"banana", "kiwi", "oatmeal", "coconut"};

public objectAdapter (Context context){
    this.context = context;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ImageView img;
    if (convertView == null){
        img = new ImageView(context);
        img.setLayoutParams(new GridView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
    }
    else{
        img = (ImageView) convertView;
    }
    img.setImageResource(image_id[position]);
    return img;
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public Object getItem(int position) {
    return null;
}

@Override
public int getCount() {
    return image_id.length;
}

}

如果需要，以下是我的MainActivity和activity_main.xml文件：

MainActivity：

public class MainActivity extends Activity {

GridView gridview_id;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    gridview_id = (GridView) findViewById(R.id.gridview_id);
    gridview_id.setAdapter(new objectAdapter(this) );
    gridview_id.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        }
    });

}
}

activity_main.xml中：

<?xml version="1.0" encoding="utf-8"?>

android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"
android:numColumns="auto_fit"
android:stretchMode="columnWidth"
android:horizontalSpacing="2dp"
android:verticalSpacing="2dp"
android:id="@+id/gridview_id">

如果你知道如何解决这个问题，请告诉我 我真的很感激。