Android“尝试在关闭游标后尝试访问游标” [英] Android "attempted to access a cursor after it has been closed"

问题描述

我正在尝试修改 HelloGridView 示例，我可以显示存储在SD上的图像的缩略图而不是res / drawable中的图像。这个想法是先在ImageView.initialize（）函数中创建一个包含图像的列表，并使用它，就像在示例中一样。

I'm trying to adapt the HelloGridView example so that I can show image thumbnails of images stored on the SD instead of images in the res/drawable. The idea is to create a list with the images first in the ImageView.initialize() function and the use it pretty much exactly as in the example.

我的光标遇到了麻烦，首先我尝试在Imageview.initialize（）函数中将其设置为私有（它仅被注释掉，以便您可以看到它的所在位置），因为在我看来，它似乎仅在此处使用，但是后来我出现错误在关闭游标后尝试访问游标。在行的onCreate（）函数中

I'm having trouble with my cursor, first I tried to have it as private in the Imageview.initialize() function (it's only commented away so you can see where I had it) since to me it seems like it is only being used there but then I got the error "Attempted to access a cursor after it has been closed." in the onCreate() function at the line

gridview.setAdapter（imageAdapter）;

gridview.setAdapter(imageAdapter);

以某种方式使用它。下一个尝试是将游标设置为 global，然后在该行之后将其关闭，但是我遇到了同样的错误，但是现在当我离开onCreate（）时。
这就是现在的代码，我不知道该怎么做。另外，如果您发现任何其他看起来很奇怪的东西，也请告诉我，因为我在android和java上是非常新的。

so this line obviously uses it somehow. Next try was to have the cursor as "global" and close it after that line instead but i get the same error but now when I'm leaving the onCreate(). This is how the code is now and I have no clue what to do. Also if you find anything else that looks odd please let me know since I'm very very new at android and java.

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;
    }
}

推荐答案

Android在关闭游标后试图访问游标

Android "attempted to access a cursor after it has been closed"

在工作/访问数据时在 Cursor 中，它需要打开！

While you are working / accessing to data in Cursor, it needs to be opened!

通常建议关闭任何数据源 >和光标在Activity的生命周期方法中，是 onStop（）或 onDestroy（）

Generally is recommended to close any datasources and cursors in Activity's life-cycle method either onStop() or onDestroy() method.

基本示例：

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

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