本文為單張圖片的內(nèi)存緩存的示例

1形病、首先創(chuàng)建LruCache緩存工具類(lèi), 拿出最大可用內(nèi)存的八分之一，作為圖片緩存的大小霞幅。

/**
 * 圖片的內(nèi)存緩存工具類(lèi)
 */
class CacheUtils {

    companion object{

        lateinit var mMemoryCache : LruCache<String, Bitmap>
        private var  maxMemory by Delegates.notNull<Int>()
        private var  cacheSize by Delegates.notNull<Int>()

        fun  initCacheAbout(){
            // 獲得虛擬機(jī)能提供的最大內(nèi)存漠吻，超過(guò)這個(gè)大小會(huì)拋出OutOfMemory的異常
            maxMemory = (Runtime.getRuntime().maxMemory() / 1024).toInt()
            cacheSize = maxMemory / 8
            mMemoryCache = ImageCache(cacheSize)
        }

        fun addBitmapToMemoryCache(key: String?, bitmap: Bitmap?) {
            if (getBitmapFromMemCache(key) == null) {
                Log.d("Neo","addBitmapToMemoryCache（存之前），長(zhǎng)度="+mMemoryCache.size())
                mMemoryCache.put(key, bitmap)
                Log.d("Neo","addBitmapToMemoryCache（存完之后）司恳，長(zhǎng)度="+mMemoryCache.size())
            }
        }

        fun getBitmapFromMemCache(key: String?): Bitmap? {
            Log.d("Neo","getBitmapFromMemCache() temp=$mMemoryCache")
            Log.d("Neo","getBitmapFromMemCache() 長(zhǎng)度="+mMemoryCache.size())
            Log.d("Neo","getBitmapFromMemCache() temp[key]="+mMemoryCache[key])
            return mMemoryCache[key]
        }

        class ImageCache(cacheSize: Int) : LruCache<String, Bitmap>(cacheSize) {
            override fun sizeOf(key: String?, value: Bitmap?): Int {
                return value!!.byteCount / 1024
            }
        }
    }
}

2途乃、創(chuàng)建圖片下載工具類(lèi)

public class BitmapUtil {

    /**
     * HttpURLConnection下載圖片并轉(zhuǎn)化為bitmap
     * @param imgUrl
     * @return
     */
    public static Bitmap getBitmapFromNet(String imgUrl) {
        try {
            //生成url
            URL url = new URL(imgUrl);
            //建立連接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            //設(shè)置超時(shí) 5s
            connection.setConnectTimeout(5000);
            //設(shè)置請(qǐng)求方法
            connection.setRequestMethod("GET");
            //連接成功
            if (connection.getResponseCode()==200){
                //獲取輸入流
                InputStream in=connection.getInputStream();
                //將流轉(zhuǎn)化為bitmap
                return BitmapFactory.decodeStream(in);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

3、使用LruCache扔傅。

• 首先判斷內(nèi)存里是否有圖片緩存耍共，如果有直接顯示；
• 如果沒(méi)有猎塞，則需要通過(guò)HttpURLConnection下載试读，如果下載成功則將圖片存入緩存，下載失敗則存入一張默認(rèn)圖片荠耽；
• 然后讀取緩存钩骇，將圖片顯示出來(lái)；

/**
 * 【單張圖片內(nèi)存緩存】
 *
 * 殺進(jìn)程或者清空APP緩存, 緩存數(shù)據(jù)就不存在了
 */
class SingleImageMemoryCacheActivity : AppCompatActivity() {

    lateinit var imageView : ImageView
    private val oriUrl : String = "https://t7.baidu.com/it/u=2168645659,3174029352&fm=193&f=GIF"

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_single_image_memory_cache)
        imageView = findViewById(R.id.image_id)
        loadBitmap(oriUrl,imageView)
    }

    private fun loadBitmap(resId: String?, imageView: ImageView?) {
        // 查看下內(nèi)存緩存中是否緩存了這張圖片
        val bitmap = CacheUtils.getBitmapFromMemCache(resId)
        if (bitmap != null) {
            Log.d("Neo","取到指定圖片的緩存了铝量，直接展示")
            imageView?.setImageBitmap(bitmap)
        } else {
            Log.d("Neo","沒(méi)有取到指定圖片的緩存倘屹，進(jìn)行下一步")
            imageView?.setImageResource(R.drawable.ic_launcher_background)
            val task = BitmapWorkerTask(this@SingleImageMemoryCacheActivity)
            task.execute(resId)
        }
    }

    companion object {
        class BitmapWorkerTask internal constructor(context : SingleImageMemoryCacheActivity) : AsyncTask<String,String,Bitmap>(){

            private val activityReference: WeakReference<SingleImageMemoryCacheActivity> = WeakReference(context)
            private lateinit var thisUrl : String

            override fun doInBackground(vararg params: String?): Bitmap {
                val thisActivity = activityReference.get()
                //網(wǎng)絡(luò)圖片請(qǐng)求失敗，則加載本地的默認(rèn)圖片慢叨，同時(shí)緩存這張默認(rèn)圖片
                return if(BitmapUtil.getBitmapFromNet(params[0]) == null){
                    Log.d("Neo","網(wǎng)圖獲取失敗纽匙，提供一張本地圖片")
                    thisUrl = "LOCAL_IMAGE_RESOURCE"
                    BitmapFactory.decodeResource(thisActivity?.resources, R.mipmap.icon6)
                }else{
                    Log.d("Neo","網(wǎng)圖獲取成功并返回")
                    thisUrl = params[0].toString()
                    BitmapUtil.getBitmapFromNet(params[0])
                }
            }

            override fun onPostExecute(result: Bitmap?) {
                val thisActivity = activityReference.get()
                Log.d("Neo","展示圖片，并將圖片保存到內(nèi)存緩存中")
                thisActivity?.imageView?.setImageBitmap(result)
                CacheUtils.addBitmapToMemoryCache(thisUrl, result)
            }
        }
    }
}

4插爹、布局文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activitys.SingleImageMemoryCacheActivity">

    <ImageView
        android:id="@+id/image_id"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        tools:ignore="MissingConstraints" />

</androidx.constraintlayout.widget.ConstraintLayout>