Android"在关闭后尝试访问游标"

Question

我正在尝试调整HelloGridView示例,以便我可以显示存储在SD上的图像的图像缩略图,而不是res/drawable中的图像.我们的想法是首先在ImageView.initialize()函数中创建一个包含图像的列表,并使用它与示例中的完全一样.

我的光标出现问题,首先我尝试在Imageview.initialize()函数中将其设置为私有(它只是注释掉了,所以你可以看到我在哪里)因为对我来说它似乎只是被使用了然后我得到错误"在关闭后尝试访问游标".在行的onCreate()函数中

gridview.setAdapter(imageAdapter);

所以这条线显然以某种方式使用它.接下来的尝试是将光标设置为"全局"并在该行之后关闭它,但我得到相同的错误但现在当我离开onCreate()时.这就是现在代码的方式,我不知道该怎么做.此外,如果你发现其他任何看起来很奇怪的东西,请告诉我,因为我在android和java非常新.

package se.mmarks.hellogridview;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {

    private Cursor imagecursor;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        GridView gridview = (GridView) findViewById(R.id.gridview);
        ImageAdapter imageAdapter = new ImageAdapter(this, imagecursor);
        imagecursor = imageAdapter.initialize();
        gridview.setAdapter(imageAdapter);
        /* setAdapter needs the cursor,
         * this is why it is closed here and not in ImageAdapter.initialize()
        */
        imagecursor.close();

        gridview.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
            Toast.makeText(MainActivity.this, "" + position, Toast.LENGTH_SHORT).show();
            }
        });
    }
}



class ImageAdapter extends BaseAdapter {
    private ArrayList<ImageView> images = new ArrayList<ImageView>();
    Cursor imagecursor = null;


    private Context mContext;

    public ImageAdapter(Context c, Cursor cursor) {
        mContext = c;
        imagecursor = cursor;
    }

    public Cursor initialize() {
        final String[] columns = { MediaStore.Images.Thumbnails._ID };
        imagecursor = null;
        try {
            imagecursor = mContext.getContentResolver().query(
                        MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, null, null, null);
        } catch(Exception e) {
            e.printStackTrace();
        }

        if(imagecursor != null){
            int image_column_index = imagecursor.getColumnIndex(MediaStore.Images.Thumbnails._ID);
            int count = imagecursor.getCount();
            for (int i = 0; i < count; i++) {
                imagecursor.moveToPosition(i);
                int id = imagecursor.getInt(image_column_index);
                ImageView imageItem = new ImageView(mContext);
                imageItem.setId(id);
                imageItem.setImageBitmap(
                    MediaStore.Images.Thumbnails.getThumbnail(mContext.getContentResolver(), id,
                    MediaStore.Images.Thumbnails.MICRO_KIND, null));
                images.add(imageItem);
            }
            //imagecursor.close();
        }
        return imagecursor;
    }

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

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

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {  // if it's not recycled, initialize some attributes
            imageView = images.get(position);
            imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }
        return imageView;
    }
}

Answer 1

Android"在关闭后尝试访问游标"

当您正在处理/访问数据时Cursor,需要打开它!

通常建议在Activity的生命周期方法或方法中关闭任何数据源和游标.onStop()onDestroy()

基本示例:

public void onDestroy() {
   super.onDestroy();
   if (cursor != null) {
      c.close();
   }
   if (db != null) {
      db.close();
   }
}