bitmap缓存——内存缓存

1.获取LruCache对象

 /**
     *  获取内存的1/8用作缓存空间
     */
    private fun getCache(): LruCache<String, Bitmap> {
        val maxMemory = Runtime.getRuntime().maxMemory()/1024
        val cacheSize = maxMemory / 8
        val lruCache = LruCache<String, Bitmap>(cacheSize.toInt())
        return lruCache
    }

2.根据key来获取Bitmap

  /**
     * 获取缓存
     * @param key
     */
    private fun getBitmapFromMemeory(key:String):Bitmap{
        return mLruCache?.get(key)!!
    }

3.增加bitmap到缓存

    /**
     * 增加bitmap到缓存
     * @param key
     * @param bitmap
     */
    private fun addBitmapToMemeory(key:String,bitmap:Bitmap){
        if (getBitmapFromMemeory(key) == null){
            mLruCache?.put(key,bitmap)
        }
    }

4.通过给定资源来源，和显示的imageView来加载图片

   /**
     *  imageView 加载图片
     *  @param resId 资源id
     *  @param imageView
     */
    fun loadBitmap(resId:Int,imageView: ImageView){
        val key = resId.toString()
        val bitmap = mLruCache?.get(key)
        if (bitmap != null){
            imageView.setImageBitmap(bitmap)
        }else{
            val bitmapWorkerTask = BitmapWorkerTask(this, imageView) //无缓存 加载任务异步执行
            bitmapWorkerTask.execute(resId)
        }
    }

5.BitmapWorkerTask继承AsyncTask,实现异步加载图片

 1 class BitmapWorkerTask extends AsyncTask{
 2 
 3     private Context mContext;
 4     private final WeakReference mImageViewReference;
 5     private int data = 0;
 6 
 7     public BitmapWorkerTask(Context context,ImageView imageView) {
 8         mImageViewReference = new WeakReference(imageView);
 9         this.mContext = context;
10     }
11 
12 
13     /**
14      * 异步执行代码
15      * @param objects
16      * @return
17      */
18     @Override
19     protected Object doInBackground(Object[] objects) {
20         data = (int) objects[0];
21         return decodeSampledBitmapFromResource(mContext.getResources(),data,100,100);
22     }
23 
24     /**
25      * 执行完成UI线程执行代码
26      * @param o
27      */
28     @Override
29     protected void onPostExecute(Object o) {
30         if (isCancelled()){
31             o = null;
32         }
33 
34         if (mImageViewReference != null && o != null){
35             final ImageView imageView = (ImageView) mImageViewReference.get();
36             final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
37             if (this == bitmapWorkerTask && imageView !=null) {
38                 imageView.setImageBitmap((Bitmap) o);
39             }
40         }
41     }
42 
43     /**
44      * 获取合适的Bitmap
45      * @param res
46      * @param resId
47      * @param reqWidth
48      * @param reqHeight
49      * @return
50      */
51     public Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
52                                                   int reqWidth, int reqHeight) {
53 
54         // First decode with inJustDecodeBounds=true to check dimensions
55         final BitmapFactory.Options options = new BitmapFactory.Options();
56         options.inJustDecodeBounds = true;
57         BitmapFactory.decodeResource(res, resId, options);
58 
59         // Calculate inSampleSize
60         options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
61 
62         // Decode bitmap with inSampleSize set
63         options.inJustDecodeBounds = false;
64         return BitmapFactory.decodeResource(res,resId, options);
65     }
66 
67     /**
68      * 根据给定宽高计算出缩放值
69      * @param options
70      * @param reqWidth
71      * @param reqHeight
72      * @return
73      */
74     private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
75         int outHeight = options.outHeight;
76         int outWidth = options.outWidth;
77         int inSampleSie = 1;
78         if (outHeight>reqHeight || outWidth>reqWidth){
79             int halfHeight = outHeight / 2;
80             int halfWidth = outWidth / 2;
81             while (halfHeight/inSampleSie>reqHeight && halfWidth/inSampleSie > reqWidth){
82                 inSampleSie*=2;
83             }
84         }
85         return inSampleSie;
86     }
87 }