ImageLoader

public class MainActivity extends AppCompatActivity {

//图片路径

    String[] images = {
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383264_8243.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383248_3693.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383243_5120.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383242_3127.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383242_9576.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383242_1721.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383219_5806.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383214_7794.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383213_4418.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383213_3557.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383210_8779.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383172_4577.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383166_3407.jpg",
            "https://img-my.youkuaiyun.com/uploads/201407/26/1406383166_2224.jpg"
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ImageView imageView = (ImageView) findViewById(R.id.imageView);
        //得到imageLoader的实例;
        ImageLoader imageLoader = ImageLoader.getInstance();
        DisplayImageOptions displayImageOptions = new DisplayImageOptions.Builder()

                .showImageOnLoading(R.mipmap.ic_launcher)  //设置图片在下载期间显示的图片

                .showImageForEmptyUri(R.mipmap.ic_launcher)  //设置图片Uri为空或是错误的时候显示的图片
                .showImageOnFail(R.mipmap.ic_launcher)  //设置图片加载/解码过程中错误时候显示的图片
                .build();
        imageLoader.displayImage(images[2], imageView);
    }

}

/**这个是系统全局的Application, 它就是系统生命周期最长的上下文;
 * 系统已启动,并不是直接进入MainActivity;二十先进入Application;
 * 重写他的目的是,初始化系统全局的一些参数;比如imageLoader的全局配置;
 * 生命周期和app的生命周期一样

*/

public class App extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        Log.e("MyApplication","我走了application");
        ImageLoaderConfiguration config = new ImageLoaderConfiguration
                .Builder(this)
                .memoryCacheExtraOptions(480, 800) // max width, max height，即保存的每个缓存文件的最大长宽
                .threadPoolSize(5)//线程池内加载的数量
                .threadPriority(Thread.NORM_PRIORITY - 2)
                .denyCacheImageMultipleSizesInMemory()
                .memoryCache(new UsingFreqLimitedMemoryCache(2 * 1024 * 1024)) // You can pass your own memory cache implementation/你可以通过自己的内存缓存实现
                .memoryCacheSize(2 * 1024 * 1024)
                .tasksProcessingOrder(QueueProcessingType.LIFO)
                .defaultDisplayImageOptions(DisplayImageOptions.createSimple())
                .imageDownloader(new BaseImageDownloader(this, 5 * 1000, 30 * 1000)) // connectTimeout (5 s), readTimeout (30 s)超时时间
                .writeDebugLogs() // Remove for release app
                .build();//开始构建
        //初始化imageloader;
        ImageLoader.getInstance().init(config);
        //初始化 代码统计;
    }
}

//权限

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <application
        android:name=".App"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">