【第二篇】Volley的使用之加载图片-白红宇

【第二篇】Volley的使用之加载图片

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发布时间：2019-06-22

本文共 11963 字，大约阅读时间需要 39 分钟。

Volley加载图片有两种方式：

　　1，ImageRequest 来对网络图片进行请求，放入请求队列，获取后现在在控件上面。

　　2，NetworkImageView 最为自定义控件来自动加载网络图片。

　　3，imageloader,对图片大小，质量格式控制来按需加载图片。

下面分别举例子说明使用：

ImageRequest的使用来加载图片：

首先设计界面，是个Gridview来加载图片：

activity_main.xml

GridView的item布局文件如下，上面是图片，下面是文字说明：

下面是主要的图片加载的逻辑代码，流程如下：

　　1，创建请求队列mQueue；

　　2，创建ImageRequest 请求，并进行配置，并将请求放入请求队列mqueue中去；

　　3，ImageRequest只有一个构造方法：对图片大小和图片格式进行设置；

/**     * Creates a new image request, decoding to a maximum specified width and     * height. If both width and height are zero, the image will be decoded to     * its natural size. If one of the two is nonzero, that dimension will be     * clamped and the other one will be set to preserve the image's aspect     * ratio. If both width and height are nonzero, the image will be decoded to     * be fit in the rectangle of dimensions width x height while keeping its     * aspect ratio.     *     * @param url URL of the image 网络图片Url     * @param listener Listener to receive the decoded bitmap 接收网络图片的bitmap回调参数     * @param maxWidth Maximum width to decode this bitmap to, or zero for none 宽     * @param maxHeight Maximum height to decode this bitmap to, or zero for 高     *            none     * @param decodeConfig Format to decode the bitmap to 编码质量的配置     * @param errorListener Error listener, or null to ignore errors 加载图片失败的回调     */    public ImageRequest(String url, Response.Listener
     
       listener, int maxWidth, int maxHeight,            Config decodeConfig, Response.ErrorListener errorListener) {        super(Method.GET, url, errorListener);        setRetryPolicy(                new DefaultRetryPolicy(IMAGE_TIMEOUT_MS, IMAGE_MAX_RETRIES, IMAGE_BACKOFF_MULT));        mListener = listener;        mDecodeConfig = decodeConfig;        mMaxWidth = maxWidth;        mMaxHeight = maxHeight;    }

package com.soyoungboy.volleydemo;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.Bitmap.Config;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.GridView;import android.widget.ImageView;import android.widget.TextView;import com.android.volley.RequestQueue;import com.android.volley.Response;import com.android.volley.Response.ErrorListener;import com.android.volley.VolleyError;import com.android.volley.toolbox.ImageRequest;import com.android.volley.toolbox.Volley;/** * Volley使用demo *  * @author soyoungboy */public class MainActivity extends Activity {    private static final String[] URLS = {        "https://img-my.csdn.net/uploads/201403/03/1393854094_4652.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_6138.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_1323.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_8439.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854083_6511.jpg",    "https://img-my.csdn.net/uploads/201403/03/1393854083_2323.jpg" };    private static final String[] DESCS = { "photo1", "photo2", "photo3",        "photo4", "photo5", "photo6" };    private RequestQueue mQueue;    private GridView gvImages;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        gvImages = (GridView) findViewById(R.id.gvImages);        GridAdapter adpater = new GridAdapter();        gvImages.setAdapter(adpater);        mQueue = Volley.newRequestQueue(this);    }    class GridAdapter extends BaseAdapter {        private LayoutInflater layoutInflater;        public GridAdapter() {            layoutInflater = LayoutInflater.from(MainActivity.this);        }        @Override        public int getCount() {            return URLS.length;        }        @Override        public Object getItem(int position) {            return URLS[position];        }        @Override        public long getItemId(int position) {            return position;        }        @Override        public View getView(int position, View convertView, ViewGroup parent) {            ViewHolder viewHolder;            if (convertView == null) {                viewHolder = new ViewHolder();                convertView = layoutInflater.inflate(R.layout.grid_item, null);                viewHolder.ivImage = (ImageView) convertView                        .findViewById(R.id.ivImage);                viewHolder.tvDesc = (TextView) convertView                        .findViewById(R.id.tvDesc);                convertView.setTag(viewHolder);            } else {                viewHolder = (ViewHolder) convertView.getTag();            }            loadImgByVolley(URLS[position], viewHolder.ivImage);            viewHolder.tvDesc.setText(DESCS[position]);            return convertView;        }    }    static class ViewHolder {        ImageView ivImage;        TextView tvDesc;    }    public void loadImgByVolley(String imgUrl, final ImageView imageView) {        ImageRequest imgRequest = new ImageRequest(imgUrl,                new Response.Listener
     
      () {            /**             * 加载成功             * @param arg0             */            @Override            public void onResponse(Bitmap arg0) {                imageView.setImageBitmap(arg0);            }        }, 300, 200, Config.ARGB_8888,         new ErrorListener() {            //加载失败            @Override            public void onErrorResponse(VolleyError arg0) {                imageView.setImageResource(R.drawable.ic_launcher);            }        });        //将图片加载放入请求队列中去        mQueue.add(imgRequest);    }}

效果：

NetworkImageView加载图片：

首先在布局中使用NetWorkImageView:

java代码里面实现：

package com.soyoungboy.volleydemo;import android.app.Activity;import android.os.Bundle;import com.android.volley.RequestQueue;import com.android.volley.toolbox.ImageLoader;import com.android.volley.toolbox.NetworkImageView;import com.android.volley.toolbox.Volley;public class NetworkImageViewActivity extends Activity {    private NetworkImageView load_img;    private ImageLoader imageLoader;    private RequestQueue requestQueue;    private LruImageCache lruImageCache;    private static final String IMGURL = "http://imgsrc.baidu.com/forum/w%3D580/sign=f96acdfc08f79052ef1f47363cf1d738/cb2fc65c10385343223c39ce9213b07ecb808870.jpg";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_networkimageview);        load_img = (NetworkImageView) findViewById(R.id.load_img);        lruImageCache = LruImageCache.getInstance();        requestQueue = Volley.newRequestQueue(this);        imageLoader = new ImageLoader(requestQueue, lruImageCache);        load_img.setImageUrl(IMGURL, imageLoader);    }}

LruImageCache.java缓存类：

package com.soyoungboy.volleydemo;import android.graphics.Bitmap;import android.support.v4.util.LruCache;import com.android.volley.toolbox.ImageLoader.ImageCache;public class LruImageCache implements ImageCache{    private static LruCache
     
       mMemoryCache;        private static LruImageCache lruImageCache;        private LruImageCache(){        // Get the Max available memory        int maxMemory = (int) Runtime.getRuntime().maxMemory();        int cacheSize = maxMemory / 8;        mMemoryCache = new LruCache
      
       (cacheSize){            @Override            protected int sizeOf(String key, Bitmap bitmap){                return bitmap.getRowBytes() * bitmap.getHeight();            }        };            }        public static LruImageCache getInstance(){        if(lruImageCache == null){            lruImageCache = new LruImageCache();        }        return lruImageCache;    }        @Override    public Bitmap getBitmap(String arg0) {                return mMemoryCache.get(arg0);        }    @Override    public void putBitmap(String arg0, Bitmap arg1) {        if(getBitmap(arg0) == null){            mMemoryCache.put(arg0, arg1);        }            }}

其中LruImageCache是个Lru算法类，主要用于处理缓存的大小问题，可以避免加载图片的时候oom的问题，ImaageLoader是volley提供的另外一种加载图片的方式。最后通过setImageUrl(String url, ImageLoader imageLoader)来进行加载。

NetworkImageView的优势在于他能够根据组件的大小自动进行图片的大小缩放处理。后面文章会在源码分析中进行讲解。

效果：

ImageLoader加载图片：

帮我们对图片进行缓存，还可以过滤掉重复的链接，避免重复发送请求。

　　1，创建请求队列；

　　2，创建imageloader对象，其中imageloader的构造方法第二个参数为imageCache的实现类，实现图片缓存的算法类。

　　3，创建imagelistener对象，主要设置图片加载失败和加载过程中的图片设置。

界面如上面第一个的界面activity_main.xml;

这里主要看下逻辑：

package com.soyoungboy.volleydemo.activity;import android.app.Activity;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.GridView;import android.widget.ImageView;import android.widget.TextView;import com.android.volley.RequestQueue;import com.android.volley.toolbox.ImageLoader;import com.android.volley.toolbox.ImageLoader.ImageListener;import com.android.volley.toolbox.Volley;import com.soyoungboy.volleydemo.LruImageCache;import com.soyoungboy.volleydemo.R;public class ImageLoaderActivity extends Activity {    private GridView gvImages;    private static final String[] URLS = {        "https://img-my.csdn.net/uploads/201403/03/1393854094_4652.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_6138.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_1323.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854084_8439.jpg",        "https://img-my.csdn.net/uploads/201403/03/1393854083_6511.jpg",    "https://img-my.csdn.net/uploads/201403/03/1393854083_2323.jpg" };    private static final String[] DESCS = { "photo1", "photo2", "photo3",        "photo4", "photo5", "photo6" };    private RequestQueue mQueue;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        gvImages = (GridView) findViewById(R.id.gvImages);        mQueue = Volley.newRequestQueue(this);        GridAdapter adpater = new GridAdapter();        gvImages.setAdapter(adpater);    }    class GridAdapter extends BaseAdapter {        private LayoutInflater layoutInflater;        private ImageLoader imageLoader;        public GridAdapter() {            layoutInflater = LayoutInflater.from(ImageLoaderActivity.this);            imageLoader = new ImageLoader(mQueue, LruImageCache.getInstance());        }        @Override        public int getCount() {            return URLS.length;        }        @Override        public Object getItem(int position) {            return URLS[position];        }        @Override        public long getItemId(int position) {            return position;        }        @Override        public View getView(int position, View convertView, ViewGroup parent) {            ViewHolder viewHolder;            if (convertView == null) {                viewHolder = new ViewHolder();                convertView = layoutInflater.inflate(R.layout.grid_item, null);                viewHolder.ivImage = (ImageView) convertView                        .findViewById(R.id.ivImage);                viewHolder.tvDesc = (TextView) convertView                        .findViewById(R.id.tvDesc);                convertView.setTag(viewHolder);            } else {                viewHolder = (ViewHolder) convertView.getTag();            }            loadImgByVolley(URLS[position], viewHolder.ivImage);            viewHolder.tvDesc.setText(DESCS[position]);            return convertView;        }        private void loadImgByVolley(String string, ImageView ivImage) {            ImageListener listener = ImageLoader.getImageListener(ivImage,                    R.drawable.ic_launcher, R.drawable.ic_launcher);            imageLoader.get(string, listener);        }    }    static class ViewHolder {        ImageView ivImage;        TextView tvDesc;    }}

界面效果：

转载地址：http://wvnva.baihongyu.com/

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