Android Caching Bitmaps Learning

Android Caching Bitmaps Learning

Reference link:

Displaying Bitmaps Efficiently

Caching Bitmaps Translation

Let's talk about it first: google has errors in the examples, and Chinese translation has not removed the errors.

Google official Download the sample

You can also refer to guolin's article,

After some learning, the preliminary practice is completed. Post it and use it for backup.

package com.akm.testlrucache;import android.app.Activity;import android.content.Context;import android.content.res.Resources;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.support.v4.util.LruCache;import android.util.DisplayMetrics;import android.view.Window;import android.view.WindowManager;import android.widget.ImageView;public class BitmapCacheUtil {private Context context;private int screenWidth = 0; private int screenHeight = 0;private final int TITLE_HEIGHT = 48;private ImageView imageView;private int resid;private LruCache
 
   mMemoryCache;  private BitmapWorkerTask  task ;  public BitmapCacheUtil(Context context , ImageView imageView,int resid) {this.context = context;this.imageView = imageView;this.resid =resid; int maxMemory = (int) Runtime.getRuntime().maxMemory();  int cacheSize = maxMemory / 8;  mMemoryCache = new LruCache
  
   (cacheSize) {  @Override  protected int sizeOf(String key, Bitmap bitmap) {  return bitmap.getByteCount();  }  };  loadBitmap();}public void loadBitmap() {   Bitmap bitmap = getBitmapFromMemoryCache(String.valueOf(resid));if (bitmap==null) {// mImageView.setImageResource(R.drawable.image_placeholder);task = new BitmapWorkerTask();  task.execute(resid); }else{imageView.setImageBitmap(bitmap);  } }  private Bitmap getBitmapFromMemoryCache(String key) {  return mMemoryCache.get(key);  }  private void addBitmapToMemoryCache(String key, Bitmap bitmap) {  if (getBitmapFromMemoryCache(key) == null) {  mMemoryCache.put(key, bitmap);  }  }  protected void setImageView() {  Bitmap bitmap = getBitmapFromMemoryCache(String.valueOf(resid));  if (bitmap != null) {  imageView.setImageBitmap(bitmap);  } else {  imageView.setImageResource(R.drawable.ic_launcher);  }  }  class BitmapWorkerTask extends AsyncTask
   
     {   @Override  protected Bitmap doInBackground(Integer... params) {  final Bitmap bitmap = decodeSampledBitmapFromResource(context.getResources(), params[0], getScreenWidth(context), getScreenHeight(context));addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);return bitmap;}  @Override  protected void onPostExecute(Bitmap bitmap) {  super.onPostExecute(bitmap);  if (bitmap != null) {  imageView.setImageBitmap(bitmap);   }  }   }  public Bitmap decodeSampledBitmapFromResource(Resources res, int resId,int reqWidth, int reqHeight) {// First decode with inJustDecodeBounds=true to check dimensionsfinal BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeResource(res, resId, options);// Calculate inSampleSizeoptions.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);// Decode bitmap with inSampleSize setoptions.inJustDecodeBounds = false;return BitmapFactory.decodeResource(res, resId, options);}public int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {// Raw height and width of imagefinal int height = options.outHeight;final int width = options.outWidth;int inSampleSize = 1;if (height > reqHeight || width > reqWidth) {if (width > height) {inSampleSize = Math.round((float)height / (float)reqHeight);} else {inSampleSize = Math.round((float)width / (float)reqWidth);}}return inSampleSize;}public void cancelTask() {  if (task != null) {  task.cancel(false);  }  }  @SuppressWarnings("deprecation")public int getScreenWidth(Context context) {if (screenWidth != 0) {return screenWidth;}WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);screenWidth = wm.getDefaultDisplay().getWidth();return screenWidth;}@SuppressWarnings("deprecation")public int getScreenHeight(Context context) {if (screenHeight != 0) {return screenHeight;}int top = 0;if (context instanceof Activity) {top = ((Activity) context).getWindow().findViewById(Window.ID_ANDROID_CONTENT).getTop();if (top == 0) {top = (int) (TITLE_HEIGHT * getScreenDensity(context));}}WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);screenHeight = wm.getDefaultDisplay().getHeight() - top;return screenHeight;}public float getScreenDensity(Context context) {WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);DisplayMetrics metric = new DisplayMetrics();wm.getDefaultDisplay().getMetrics(metric);return metric.density;}public float getScreenDensityDpi(Context context) {WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);DisplayMetrics metric = new DisplayMetrics();wm.getDefaultDisplay().getMetrics(metric);return metric.densityDpi;}}