如何在ArrayList中存储大型位图

Question

I am using below code this way but when I add images into ArrayList after sometime my app crashes and it goes out of memory error

                    ArrayList<Bitmap> rev = new ArrayList<Bitmap>(10000);
                    for (long i = 1000000; i < millis * 1000; i += 1000000) 
                    {

                            finalBitmap = retriever.getFrameAtTime(i,MediaMetadataRetriever.OPTION_CLOSEST_SYNC);
                            rev.add(finalBitmap);
                            try
                            {
                                ByteArrayOutputStream bytes = new ByteArrayOutputStream();
                                finalBitmap.compress(Bitmap.CompressFormat.PNG, 40, bytes);
                                File f = new File(saveFolder, ("img0"+j+".png"));
                                f.createNewFile();
                                FileOutputStream fo = new FileOutputStream(f);
                                fo.write(bytes.toByteArray());
                                fo.flush();
                                fo.close();
                                j++;
                            }
                             catch (IOException e) 
                             {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                             }  
                        }

Answer 1

With the limited memory available you will not be able to have a direct reference to each of the images, otherwise like you say you will run out of memory. These images will take up space in memory as long as there is a reference to your BitMap objects. To free up this memory you need to dereference these BitMaps and or clear the ArrayList, this will allow the Garbage Collector to free up the unused memory. Ideally you only want a reference only to the images you can see, or the ones you will see next.

You could just look up the 8 images for every page view, or perhaps the the images in the surrounding page views. If the images you are display are much larger than the size they take up then you may want to resize these images on the fly and only store them as the size they appear, this should also help reduce the memory footprint of your images.

The Android developers have written a series of tutorials on just this topic: http://developer.android.com/training/displaying-bitmaps/index.html

Answer 2

If you need to pass an stay of images to an activity then you ate better off sending an stay of file paths to it if you can change the activity.

Otherwise you will need to new to read the bitmaps with a later sample size so they are smaller but consume less memory.

http://developer.android.com/training/displaying-bitmaps/load-bitmap.html#load-bitmap

You can use 4*width*height to determine the size of the bitmap when it's in memory and use that to determine how much memory you will allocate.

Use BitmapFactory.Option.inJustDecodeBounds to get the size of the bitmap without loading it