android - 如何避免从android资源加载大图片时出现OOM

Question

我已经开发了 20 多个 Android 应用程序，应用程序有一个由大图像幻灯片(例如 4 张尺寸为 750 x 1334 的图像)组成的教程 Activity ，并将在首次启动时向用户显示。

由于图像质量的原因，我无法再减小尺寸。

我的代码 fragment 如下；

public class GalleryImageActivity extends BaseActivity implements OnGestureListener, OnTouchListener {
ViewPager imagePager;
GalleryImageAdapter galleryImageAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.gallery_image);

    imagePager = (ViewPager) findViewById(R.id.image_pager);

    galleryImageAdapter = new GalleryImageAdapter(this);
    imagePager.setAdapter(galleryImageAdapter);
    imagePager.setOnTouchListener(this);
}
}


public class GalleryImageAdapter extends PagerAdapter {
public static int SCREEN_CNT = 4;
Bitmap[] bmp = new Bitmap[SCREEN_CNT];

@Override
public int getCount() {
    return SCREEN_CNT;
}

@Override
public Object instantiateItem(ViewGroup view, int position) {
    View view = inflater.inflate(R.layout.gallery_image_item, null);
    ImageView imv = (ImageView) view.findViewById(R.id.imgView);

    bmp[position] = readBitMap(context, R.drawable.tutorial_img_0 + position, position); 
    if (bmp[position] != null)
        imv.setImageBitmap(bmp[position]);
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {

    if (bmp[position] != null && !bmp[position].isRecycled())
    {
        bmp[position].recycle();   
        System.gc();  
        bmp[position] = null;
    }
}

public Bitmap readBitMap(Context context, int resId, int position) { 
    BitmapFactory.Options opt = new BitmapFactory.Options();
    opt.inJustDecodeBounds = true;

    InputStream is = context.getResources().openRawResource(resId);
        BitmapFactory.decodeStream(is,null, opt);
    opt.inPreferredConfig = Bitmap.Config.RGB_565;
    opt.inPurgeable = true;
    opt.inInputShareable = true;
    opt.inJustDecodeBounds = false;

    try {
        is.close();
    } catch (IOException e) {                
        e.printStackTrace();
    }

    is = context.getResources().openRawResource(resId);
    Bitmap bitmap = BitmapFactory.decodeStream(is,null, opt);      

    try {
        is.close();
    } catch (IOException e) {                
        e.printStackTrace();
    }            

    return bitmap;
}
}

有时效果很好，但是当重复5~6次时，BitmapFactory.decodeStream会抛出“内存不足”。我如何决定比例大小或解决此问题？

示例图像如下；

Answer 1

您可以修改readBitMap函数如下；

public Bitmap readBitMap(Context context, int resId, int position){ 
    if (bmp[position] == null || bmp[position].isRecycled())
    {
        BitmapFactory.Options opt = new BitmapFactory.Options();
        opt.inPreferredConfig = Bitmap.Config.RGB_565; 

        opt.inPurgeable = true;  
        opt.inInputShareable = true;        

        DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
        opt.inScaled = true;
        opt.inDensity = DisplayMetrics.DENSITY_DEFAULT; // !important

        InputStream is = context.getResources().openRawResource(resId);  
        try {               
            bmp[position] = BitmapFactory.decodeStream(is,null,opt);
        } catch (Exception e){
            bmp[position] = null;
        }           
    }

    return bmp[position];
}

某些类型的手机，尤其是三星手机，对于内存泄漏的设计并不完善。

opt.inDensity = DisplayMetrics.DENSITY_DEFAULT非常重要。

如果inDensity为0，则BitmapFactory.decodeStream将填充与资源关联的密度。 more...

当您的 Activity(或页面)被销毁时，您应该将 imageview 的位图设置为 null。