android - 在 Android 中使用 BitmapFactory.decodeStream() 从缓存中加载图像

Question

更新:即使我没有从缓存中检索图像，我也尝试通过 Drawable 检索，我将所有 18 张图像存储在“drawable-mdpi”文件夹中。仍然显示空白屏幕。

我能够从服务器检索图像并将图像 (.GIF) 保存到缓存中。但是，当我需要从缓存中加载该图像时，该图像不会显示在屏幕上。这是完成工作的代码:

    File cacheDir = context.getCacheDir();

            File cacheMap = new File(cacheDir, smallMapImageNames.get(i).toString());
            if(cacheMap.exists()){
                FileInputStream fis = null;
                try {
                    fis = new FileInputStream(cacheMap);
                    Bitmap local = BitmapFactory.decodeStream(fis);
                    puzzle.add(local);  
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }

            }else{
                Drawable smallMap = LoadImageFromWebOperations(mapPiecesURL.get(i).toString());
                if(i==0){
                    height1 = smallMap.getIntrinsicHeight();
                    width1 = smallMap.getIntrinsicWidth();
                }
                if (smallMap instanceof BitmapDrawable) { 
                    Bitmap bitmap = ((BitmapDrawable)smallMap).getBitmap();
                    FileOutputStream fos = null;
                    try {
                        cacheMap.createNewFile();
                        fos = new FileOutputStream(cacheMap);
                        bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
                        fos.flush();       
                        fos.close(); 
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }       

                    puzzle.add(bitmap);
                }
            }

存储图片名称的ArrayList:smallMapImageNames(图片名称也可以在URL中找到)

存储图片URL的ArrayList:ma​​pPiecesURL

总而言之，我有两个问题1)如何从缓存中加载图像？2) 关于 bitmap.compress()，来自服务器的图像是 .GIF 格式，但我应用 Bitmap.CompressFormat.PNG。那么这样做会有什么问题吗？

谁能帮我解决这个问题？

两个函数

    private Bitmap getBitMap(Context context) {
        // TODO Auto-generated method stub
        WifiPositioningServices wifiPositioningServices = new WifiPositioningServices();

        String[] mapURLandCalibratedPoint1 = wifiPositioningServices.GetMapURLandCalibratedPoint("ERLab-1_1.GIF","ERLab"); //list of map pieces url in the first 9 pieces
        String[] mapURLandCalibratedPoint2 = wifiPositioningServices.GetMapURLandCalibratedPoint("ERLab-4_1.GIF","ERLab"); //list of map pieces url in the last 9 pieces
        ArrayList<String> smallMapImageNames = new ArrayList<String>();
        ArrayList<String> mapPiecesURL = new ArrayList<String>();

        for(int i=0; i<mapURLandCalibratedPoint1.length; i++){
                if(mapURLandCalibratedPoint1[i].length()>40){ //image url
                    int len = mapURLandCalibratedPoint1[i].length();
                    int subStrLen = len-13;
                    smallMapImageNames.add(mapURLandCalibratedPoint1[i].substring(subStrLen, len-3)+"JPEG");
                    mapPiecesURL.add(mapURLandCalibratedPoint1[i]);
                }
                else{
                    //perform other task
                }

        }

        for(int i=0; i<mapURLandCalibratedPoint2.length; i++){
            if(mapURLandCalibratedPoint2[i].length()>40){ //image url
                int len = mapURLandCalibratedPoint2[i].length();
                int subStrLen = len-13;
                smallMapImageNames.add(mapURLandCalibratedPoint2[i].substring(subStrLen, len-3)+"JPEG");
                mapPiecesURL.add(mapURLandCalibratedPoint2[i]);
            }
            else{
                //perform other task
            }       
        }
        Bitmap result = Bitmap.createBitmap(1029, 617, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(result);
        ArrayList<Bitmap> puzzle = new ArrayList<Bitmap>();

        int height1 = 0 ;
        int width1 = 0;

        File cacheDir = context.getCacheDir();

        for(int i=0; i<18; i++){                
            File cacheMap = new File(cacheDir, smallMapImageNames.get(i).toString());
            if(cacheMap.exists()){
                //retrieved from cached
                try {           
                    FileInputStream fis = new FileInputStream(cacheMap);                
                    Bitmap bitmap = BitmapFactory.decodeStream(fis);
                    puzzle.add(bitmap);
                } catch (FileNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

            }else{
                //retrieve from server and cached it
                Drawable smallMap = LoadImageFromWebOperations(mapPiecesURL.get(i).toString());
                if(i==0){
                    height1 = smallMap.getIntrinsicHeight();
                    width1 = smallMap.getIntrinsicWidth();
                }
                if (smallMap instanceof BitmapDrawable) { 
                    Bitmap bitmap = ((BitmapDrawable)smallMap).getBitmap();
                    FileOutputStream fos = null;
                    try {
                        cacheMap.createNewFile();
                        fos = new FileOutputStream(cacheMap);
                        bitmap.compress(CompressFormat.JPEG, 100, fos);
                        fos.flush();       
                        fos.close(); 
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }       

                    puzzle.add(bitmap);
                }
            }       
        }

        Rect srcRect;
        Rect dstRect;
        int cnt =0;


        for (int j = 0; j < 3; j++) {
            int newHeight = height1 * (j % 3);
            for (int k = 0; k < 3; k++) {
                if (j == 0 && k == 0) {
                    srcRect = new Rect(0, 0, width1, height1);
                    dstRect = new Rect(srcRect);
                } else {
                    int newWidth = width1 * k;
                    srcRect = new Rect(0, 0, width1, height1);
                    dstRect = new Rect(srcRect);
                    dstRect.offset(newWidth, newHeight);
                }
                canvas.drawBitmap(puzzle.get(cnt), srcRect, dstRect,null);
                cnt++;
            }
        }

        for(int a=0; a<3; a++){
            int newHeight = height1 * (a % 3);
            for (int k = 3; k < 6; k++) {
                if (a == 0 && k == 0) {
                    srcRect = new Rect(0, 0, width1*3, height1);
                    dstRect = new Rect(srcRect);
                } else {
                    int newWidth = width1 * k;
                    srcRect = new Rect(0, 0, width1, height1);
                    dstRect = new Rect(srcRect);
                    dstRect.offset(newWidth, newHeight);
                }
                canvas.drawBitmap(puzzle.get(cnt), srcRect, dstRect,
                        null);
                cnt++;
            }
        }
        return result;
    }

    private Drawable LoadImageFromWebOperations(String url) {
        // TODO Auto-generated method stub
        try
        {
            InputStream is = (InputStream) new URL(url).getContent();
            Drawable d = Drawable.createFromStream(is, "src name");
            return d;
        }catch (Exception e) {
            System.out.println("Exc="+e);
            return null;
        }
    }

我实际上是在尝试显示 18 张 (3X6) 的图像以形成平面图。所以为了显示图像，我使用两个 for-loop 来显示它。两个 .GIF 图像 ERLab-1_1.GIF 和 ERLab-4_1.GIF 是每个组的中心部分。例如，第一行将是 ERLab-0_0.GIF、ERLab-1_0.GIF、ERLab-2_0.GIF、ERLab-3_0.GIF、ERLab-4_0.GIF、ERLab-5_0.GIF。第二行是 XXX-X_1.GIF，第三行是 XXX-X_2.GIF。

最后，

Bitmap resultMap = getBitMap(this.getContext());
bmLargeImage = Bitmap.createBitmap(1029 , 617, Bitmap.Config.ARGB_8888);
bmLargeImage = resultMap;

然后在 onDraw 函数中将图像绘制到 Canvas 上。

Answer 1

我刚刚解决了我自己的问题。

在这一行中，canvas.drawBitmap(puzzle.get(cnt), srcRect, dstRect,null);在我使用它将位图绘制到 Canvas 上的每个 for 循环中，我需要将 ArrayList(拼图)中的每个项目转换为位图。只有这样，图像才会显示。

我认为如果 ArrayList 本身是确定的，ArrayList<Bitmap> puzzle = new ArrayList<Bitmap>(); ArrayList 中的每个项目都是位图类型。但这不总是如此吗？