Android 自定义 SimpleCursorAdapter 带有来自文件中的图像和数据库中的路径

Question

要点：自定义适配器通过数据库中的文件路径间接获取文件资源。效率低下/内存问题。征求您的意见。

所有搜索的引用、相关链接和有用的话题都在帖子底部。

以下代码有效，但有几个因素值得关注。需要一些更有经验的眼睛来建议改进或避免潜在的错误。应用程序不需要是内容提供者（仅来自应用程序的本地数据）。有问题的 ListView 重量很轻，只有大约 5 到最多 10 个条目。 （我省略了数据库的东西，因为它可以工作。）

概述：

• DataBase 包含一些文本和一个图像文件路径。 - 好的
• 图像文件存储在设备上（SD 卡/外部存储，无论何时）。 - 好的

文件不在数据库中，这与普通的 SimpleCursorAdapter 不同 - 必须提取图像文件。在填充列表视图之前添加了将其制作为缩略图的开销。

如上所述，它很轻，但是，即使只有一两个条目，VM 也会打嗝。我怀疑这都是与位图相关的内存抖动：

08-27 19:53:14.273: I/dalvikvm-heap(11900): Grow heap (frag case) to 4.075MB for 1228816-byte allocation
08-27 19:53:14.393: D/dalvikvm(11900): GC_CONCURRENT freed <1K, 5% free 4032K/4244K, paused 13ms+3ms, total 116ms

---

/* myTextAndImageCursorAdapter.java */

import android.widget.SimpleCursorAdapter;

//import android.support.v4.widget.SimpleCursorAdapter;
import android.content.Context;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import android.database.Cursor;
import java.io.File;

import android.widget.ImageView;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import static android.media.ThumbnailUtils.extractThumbnail;


public class TextAndImageCursorAdapter extends SimpleCursorAdapter { 

    private Context context;
    private int layout;

    public TextAndImageCursorAdapter (Context ctx, int layout, Cursor c, String[] from, int[] to) {
        super(context, layout, c, from, to);
        this.context = ctx;
        this.layout = layout;
    }

    @Override
    public View newView(Context ctx, Cursor cursor, ViewGroup parent) {

        Cursor c = getCursor();

        final LayoutInflater inflater = LayoutInflater.from(ctx);
        View vView = inflater.inflate(layout, parent, false);

        int iCol_Text = c.getColumnIndex(DBCOL_TEXT);
        int iCol_Image = c.getColumnIndex(DBCOL_IMAGE);

        String sText = c.getString(iCol_Text);
        String sFileAndPath_Image = c.getString (iCol_Image);  //// sImage path & file

        TextView tvText = (TextView) v.findViewById(R.id.gui_text);
        if (tvText != null) {
            tvText.setText(sSomeText);
        }

        ImageView ivImage (ImageView) v.findViewById(R.id.gui_image);
        if (ivImage != null) {
            ivImage.setImage (mySetImage (sFileAndPath_Image) );
        }

        return vView;
    }

    @Override
    public void bindView(View v, Context ctx, Cursor c) {
        //// ( like newView(), without an inflater, view, or return ) 
        int iCol_Text = c.getColumnIndex(DBCOL_TEXT);
        int iCol_Image = c.getColumnIndex(DBCOL_IMAGE);

        String sText = c.getString(iCol_Text);
        String sFileAndPath_Image = c.getString (iCol_Image);  //// path & file

        TextView tvText = (TextView) v.findViewById(R.id.gui_text);
        if (tvText != null) {
            tvText.setText(sSomeText);
        }

        ImageView ivImage (ImageView) v.findViewById(R.id.gui_image);
        if (ivImage != null) {
            ivImage.setImageBitmap ( mySetImage ( sFileAndPath_Image ) ) ;
        }
    }
    /////
    /////
    protected Bitmap mySetImage ( String path ) {
        int width = 60; int height = 40 ;

        File imgFile = new File ( path );  //// usually like: \sdcard0\wherever\filename1234.bmp
        Bitmap myBitmap = null;

        if( imgFile.exists() )
        {
                myBitmap = BitmapFactory.decodeFile ( imgFile.getAbsolutePath () );                  
        }
            else                    
                Log.d ("oops", "no image file ... using default.");
                myBitmap = getTheDefaultImage ();  //// not shown - this is arbitrary
        }

        imgFile.close();
        return ( extractThumbnail ( myBitmap, width, height ) ) ;
    }      
}

[编辑 - 添加链接] 搜索条件： " Android 自定义 simplecursoradapter，带有来自数据库中路径的文件中的图像 "

最近的命中，但尝试从 res 中提取图像，而不是从外部/sd 存储（未回答）： SimpleCursorAdapter how to show an image?

也是近乎命中/未命中 - 类似算法（未回答）参考 4）： Customizing list shown from SimpleCursorAdapter using ViewBinder

几乎，但 OP 的代码不起作用，（没有有效的答案）： Load Image in a custom list by SimpleCursorAdapter

为 OP 工作，但使用 JSON 进行远程检索，而不是本地检索（也许这可以调整，但我不清楚如何）。 How to show images in imageview in simple adapter?

不完全是，但再次关闭： ListView scroll slow while loading image from Internal Storage

Image Loader 问题（参考文献 2）： Imageloader not loading image on real device

相关链接：

Android Custom Cursor Adapter

Android: Issue with newView and bindView in custom SimpleCursorAdapter

同名点击，但与我的具体问题无关 - 这些通常是指应用内资源： show image from database where you saved the path of image

Custom SimpleCursorAdapter error

Custom SimpleCursorAdapter, database query and NullPointerException

nullPointerException with extended SimpleCursorAdapter

Android SimpleCursorAdapter - Adding conditional images

外部参考：

0) 自定义光标适配器的简单介绍 http://thinkandroid.wordpress.com/2010/01/11/custom-cursoradapters/

1) Romain Guy - 基本布局... 2 txts, 1 image http://www.curious-creature.org/2009/02/22/android-layout-tricks-1/

2) AQuery（Android 查询） http://code.google.com/p/android-query/wiki/ImageLoading

3) Android 缩略图 http://developer.android.com/reference/android/media/ThumbnailUtils.html

4) 定制。带有“开/关”星形图像的列表视图： http://enjoyandroid.wordpress.com/2012/03/12/customizing-simple-cursor-adapter/

Answer 1

你可以做两件事：

1) 使用 ViewHolder 模式，缓存 LayoutInfalter 最重要的是：不要绑定数据两次：

/* ... imports */

import static android.media.ThumbnailUtils.extractThumbnail;

public class TextAndImageCursorAdapter extends SimpleCursorAdapter { 

    private LayoutInflater mLayoutInflater;
    private Context context;
    private int layout;


    private class ViewHolder {
        TextView textView;
        ImageView imageView;

        ViewHolder(View v) {
            textView = (TextView) v.findViewById(R.id.gui_text);
            imageView = (ImageView) v.findViewById(R.id.gui_image);
        }
    }

    public TextAndImageCursorAdapter (Context ctx, int layout, Cursor c, String[] from, int[] to) {
        super(ctx, layout, c, from, to);
        this.context = ctx;
        this.layout = layout;
        mLayoutInflater = LayoutInflater.from(ctx);
    }


    @Override
    public View newView(Context ctx, Cursor cursor, ViewGroup parent) {
        View vView = mLayoutInflater.inflate(layout, parent, false);
        vView.setTag( new ViewHolder(vView) );
        // no need to bind data here. you do in later
        return vView;// **EDITED:**need to return the view
    }

    @Override
    public void bindView(View v, Context ctx, Cursor c) {
        // you might want to cache these too
        int iCol_Text = c.getColumnIndex(DBCOL_TEXT);
        int iCol_Image = c.getColumnIndex(DBCOL_IMAGE);

        String sText = c.getString(iCol_Text);
        String sFileAndPath_Image = c.getString (iCol_Image);  //// path & file

        ViewHolder vh = (ViewHolder) v.getTag();

        vh.textView.setText(sSomeText);
        vh.imageView.setImageBitmap ( mySetImage ( sFileAndPath_Image ) );
    }
}

2) 这非常重要：不要在每次绑定时都创建缩略图。你需要缓存结果：

private void setThumbnail(String path, Bitmap b) {
    // save thumbnail to some kind of cache
    // see comment below
}

private Bitmap getThumbnail(String path) {
    Bitmap thumbnail = null;
    // try to fetch the thumbnail from some kind of cache
    // see comment below
    return thumbnail;
}

protected Bitmap mySetImage ( String path ) {
    int width = 60; int height = 40 ;

    Bitmap thumbnail = getThumbnail(path); // try to fetch thumbnail
    if (thumbnail != null) return thumbnail;

    File imgFile = new File ( path );  //// usually like: /sdcard/wherever/filename1234.bmp
    Bitmap myBitmap = null;

    if( imgFile.exists() ) {
            myBitmap = BitmapFactory.decodeFile ( imgFile.getAbsolutePath () );                  
    } else {
            Log.d ("oops", "no image file ... using default.");
            myBitmap = getTheDefaultImage ();  //// not shown - this is arbitrary
    }

    imgFile.close();
    thumbnail = extractThumbnail ( myBitmap, width, height );
    myBitmap.recycle();
    setThumbnail(path, thumbnail); // save thumbnail for later reuse
    return thumbnail;
}     

根据您的用例，您想用某种 LruCache 填充 getThumbnail() 和 setThumbnail()：

• 在 android API 和支持库中有一个可用的内存 LruCache：https://developer.android.com/reference/android/util/LruCache.html
• Jake 制作了一个持久的 DiskLruCache：https://github.com/JakeWharton/DiskLruCache

编辑：

  @Override
public View newView(Context ctx, Cursor cursor, ViewGroup parent) {
    View vView = mLayoutInflater.inflate(layout, parent, false);
    vView.setTag( new ViewHolder(vView) );
    // no need to bind data here. you do in later
    return vView;// **EDITED:**need to return the view
}