使用Androids lrucache的示例

Question

我需要帮助了解androids LruCache.我想用来将图像加载到我的gridview中,以便更好地加载/滚动.有人可以使用LruCache发布示例代码吗.提前致谢.

Answer 1

以下是我使用LruCache制作的课程,这是基于在Google I/O 2012上提供的"少花钱多办事:成为优秀Android公民"的演示文稿.

看看电影,了解我在TCImageLoader课堂上做的更多信息:

public class TCImageLoader implements ComponentCallbacks2 {
    private TCLruCache cache;

    public TCImageLoader(Context context) {
        ActivityManager am = (ActivityManager) context.getSystemService(
            Context.ACTIVITY_SERVICE);
        int maxKb = am.getMemoryClass() * 1024;
        int limitKb = maxKb / 8; // 1/8th of total ram
        cache = new TCLruCache(limitKb);
    }

    public void display(String url, ImageView imageview, int defaultresource) {
        imageview.setImageResource(defaultresource);
        Bitmap image = cache.get(url);
        if (image != null) {
            imageview.setImageBitmap(image);
        }
        else {
            new SetImageTask(imageview).execute(url);
        }
    }

    private class TCLruCache extends LruCache<String, Bitmap> {

        public TCLruCache(int maxSize) {
            super(maxSize);
        }

        @Override
        protected int sizeOf(ImagePoolKey key, Bitmap value) {
            int kbOfBitmap = value.getByteCount() / 1024;
            return kbOfBitmap;
        }
    }

    private class SetImageTask extends AsyncTask<String, Void, Integer> {
        private ImageView imageview;
        private Bitmap bmp;

        public SetImageTask(ImageView imageview) {
            this.imageview = imageview;
        }

        @Override
        protected Integer doInBackground(String... params) {
            String url = params[0];
            try {
                bmp = getBitmapFromURL(url);
                if (bmp != null) {
                    cache.put(url, bmp);
                }
                else {
                    return 0;
                }
            } catch (Exception e) {
                e.printStackTrace();
                return 0;
            }
            return 1;
        }

        @Override
        protected void onPostExecute(Integer result) {
            if (result == 1) {
                imageview.setImageBitmap(bmp);
            }
            super.onPostExecute(result);
        }

        private Bitmap getBitmapFromURL(String src) {
            try {
                URL url = new URL(src);
                HttpURLConnection connection
                    = (HttpURLConnection) url.openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                Bitmap myBitmap = BitmapFactory.decodeStream(input);
                return myBitmap;
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
    }

    @Override
    public void onLowMemory() {
    }

    @Override
    public void onTrimMemory(int level) {
        if (level >= TRIM_MEMORY_MODERATE) {
            cache.evictAll();
        }
        else if (level >= TRIM_MEMORY_BACKGROUND) {
            cache.trimToSize(cache.size() / 2);
        }
    }
}

Answer 2

我发现了一种非常简单的方法,对我来说非常有效......

这是Cache.java类.在这个类中,静态getInstance()方法使我们只能在整个应用程序中创建一个缓存实例.getLru()方法用于检索缓存的对象,稍后将显示如何使用它.此缓存是通用的,这意味着您可以将任何Object类型保存到其中.此处的高速缓存大小设置为1024.如果它太小,可以更改:

import android.support.v4.util.LruCache;

public class Cache {

    private static Cache instance;
    private LruCache<Object, Object> lru;

    private Cache() {

        lru = new LruCache<Object, Object>(1024);

    }

    public static Cache getInstance() {

        if (instance == null) {

            instance = new Cache();
        }

        return instance;

    }

    public LruCache<Object, Object> getLru() {
        return lru;
    }
}

这是活动中将位图保存到缓存的代码:

public void saveBitmapToCahche(){

        //The imageView that you want to save it's bitmap image resourse
        ImageView imageView = (ImageView) findViewById(R.id.imageViewID);

        //To get the bitmap from the imageView
        Bitmap bitmap = ((BitmapDrawable)imageview.getDrawable()).getBitmap();

        //Saving bitmap to cache. it will later be retrieved using the bitmap_image key
        Cache.getInstance().getLru().put("bitmap_image", bitmap);
    }

这是从缓存中检索位图的代码,然后将imageView设置为此位图:

public void retrieveBitmapFromCache(){

        //The imageView that you want to set to the retrieved bitmap
        ImageView imageView = (ImageView) findViewById(R.id.imageViewID);

        //To get bitmap from cache using the key. Must cast retrieved cache Object to Bitmap
        Bitmap bitmap = (Bitmap)Cache.getInstance().getLru().get("bitmap_image");

        //Setting imageView to retrieved bitmap from cache
        imageView.setImageBitmap(bitmap));

}

就这样!如您所见,这非常简单.

• 例:

在我的应用程序中,所有视图都保存在类变量中,因此可以通过类中的所有方法查看它们.在我的第一个活动中,在onClickButton()使用intent开始新活动之前,我将图像位图保存在方法中的缓存中.我还在缓存中保存了一个字符串值:

public void onClickButton(View v){

    Bitmap bitmap = ((BitmapDrawable)imageView.getDrawable()).getBitmap();
    String name = textEdit.getText().toString();

    Cache.getInstance().getLru().put("bitmap_image", bitmap);
    Cache.getInstance().getLru().put("name", name);

    Intent i = new Intent(FirstActivity.this, SecondActivity.class);
    startActivity(i);
}

然后我也使用意图从第二个活动导航到第三个活动.在上一个活动中,我将其他对象保存到缓存中,然后使用intent返回第一个活动.一旦我回到第一个活动,该onCreate()方法将开始.在该方法中,我检查我的缓存是否具有任何位图值或任何字符串值(基于我的应用程序业务):

public ImageView imageView;
public EditText editText;

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

        //...Other code...

        //The imageView that you want to save it's bitmap image resourse
        imageView = (ImageView) findViewById(R.id.imageViewID);

        //The editText that I want to save it's text into cache
        editText = (EditText)findViewById(R.id.editTextID);

        if(Cache.getInstance().getLru().get("name")!=null){
             editText.setText(Cache.getInstance().getLru().get("name").toString());
        }
        if(Cache.getInstance().getLru().get("bitmap_image")!=null){
             imageView.setImageBitmap((Bitmap)Cache.getInstance().getLru().get("bitmap_image"));
        }

        //...Other code...
    }

Answer 3

看看缓存位图,其中演示了如何使用LruCache.

该页面代码的相关部分如下: -

private LruCache mMemoryCache;

@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    // Get memory class of this device, exceeding this amount will throw an
    // OutOfMemory exception.
    final int memClass = ((ActivityManager) context.getSystemService(
            Context.ACTIVITY_SERVICE)).getMemoryClass();

    // Use 1/8th of the available memory for this memory cache.
    final int cacheSize = 1024 * 1024 * memClass / 8;

    mMemoryCache = new LruCache(cacheSize) {
        @Override
        protected int sizeOf(String key, Bitmap bitmap) {
            // The cache size will be measured in bytes rather than number of items.
            return bitmap.getByteCount();
        }
    };
    ...
}

public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
    if (getBitmapFromMemCache(key) == null) {
        mMemoryCache.put(key, bitmap);
    }
}

public Bitmap getBitmapFromMemCache(String key) {
    return mMemoryCache.get(key);
}