新手--gallery怎么不能显示图片

package com.example.gallery;

import android.app.Activity;
import android.os.Bundle;

import android.view.Menu;
import android.view.MenuItem;

import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Gallery;
import android.widget.Toast;

public class MainActivity extends Activity implements OnItemClickListener {
private Gallery gallery;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
gallery=(Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));//设置图片适配器
//点击图片监听
gallery.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {

            Toast.makeText(MainActivity.this, "点击了第"+arg2+"张图片", 
                    Toast.LENGTH_LONG).show();
        }

});

}
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {


}

}

//Adpater的class

package com.example.gallery;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter{
private Context context;
private Integer[] ima;

public ImageAdapter(Context context){
    this.context=context;
    ima=new Integer[]{

                    R.drawable.ima01,
                    R.drawable.ima02,
                    R.drawable.ima03


    };
}

@Override
public int getCount() {
    // 返回获得的图片数目
    return ima.length;
}

@Override
public Object getItem(int position) {

    return position;
}

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

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    ImageView imageview=new ImageView(context);
    imageview.setImageResource(position);
    imageview.setScaleType(ImageView.ScaleType.FIT_XY);
    imageview.setLayoutParams(new Gallery.LayoutParams(136,88));

    return imageview;
}

}

//xml

android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<Gallery
    android:id="@+id/gallery1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
   android:gravity="center_vertical"
   android:background="?android:galleryItemBackground"

/>

求各位师兄师姐解答，谢谢啦

public Object getItem(int position) {

return position;

}
这里返回的应该是ima[position]