Question

Gist：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。低效/记忆问题。您的意见要求。

对所有搜索，相关链接以及有用的主题的引用都在帖子底部。

以下代码，但有几个因素值得关注。需要一些更有经验的眼睛，请建议改善或潜在的错误，以避免。应用不需要是内容提供商（仅限应用于本地的数据）。有问题的ListView将非常轻量级，只有大约5到10个条目。（我遗漏了数据库的东西，因为它有效。）

概述：

DataBase包含一些文本和图像文件路径。 - 好的
图像文件存储在设备上（SD卡/外部存储器，无论哪里）。 - 好的

文件不在数据库中使得它与普通的SimpleCursorAdapter不同 - 必须拉动图像文件。添加了在填充listview之前将其制作成缩略图的开销。

如上所述，它很轻，但即使只有一两个条目，虚拟机也会出现问题。我怀疑这是与Bitmaps相关的所有内存抖动：

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与文件中的图像与数据库中的路径 “

最近的点击，但尝试从res中提取图像，而不是从外部/ sd存储（未应答）： SimpleCursorAdapter how to show an image?

也是一个接近命中/错过 - 类似的算法（未答复）引用4）： Customizing list shown from SimpleCursorAdapter using ViewBinder

差不多，但OP的代码不起作用，（没有正常工作的答案）： 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（可能这可以调整，但我不清楚如何）。 How to show images in imageview in simple adapter?

不完全，但又一次关闭： 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

同样命名的匹配，但与我的具体问题无关 - 这些通常指的是应用内资源： 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）简单介绍自定义游标适配器 http://thinkandroid.wordpress.com/2010/01/11/custom-cursoradapters/

1）Romain Guy - 基本布局... 2 txts，1张图片 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）客户。列表视图带有“开/关”星形图像： 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：不要在每个绑定上创建缩略图。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;
}

根据您的使用情况，您希望使用某种LruCache填充getThumbnail()和setThumbnail()：

在Android API和支持lib中有一个内存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
}

Android自定义SimpleCursorAdapter，带有来自文件的图像，带有数据库中的路径

1 个答案: