Android-Volley

Posted 2022-11-30 simplify20

一、Volley使用

翻译自Google官方指南，自己对内容进行了加工和提炼，原文：Transmitting Network Data Using Volley

创建简单的请求

关键字

• ResquestQueue && ResquestQueue.newRequestQueue
• Request
• Cache Thread && NetWorkThread && WorkerThread &&MainThread
• Cancle request && Tag

ResquestQueue:请求队列，存放请求

ResquestQueue.newRequestQueue():创建默认的请求队列

ResquestQueue.add(request):执行请求

Request:请求对象

request.cancle():取消该请求

mRequestQueue.cancelAll(TAG):取消所有tag为TAG的请求

使用Volley.newRequestQueue(context)创建默认请求队列
使用Volley.newRequestQueue(context)创建默认请求队列，再创建一个简单的StringRequest，放入到请求队列中，执行add方法后，Volley会在工作线程中执行后续的操作，不干扰主线程的运行，所有的响应都会发回主线程，以方便更新UI数据。

final TextView mTextView = (TextView) findViewById(R.id.text);
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(this);
String url ="http://www.google.com";
// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
            new Response.Listener() 
    @Override
    public void onResponse(String response) 
        // Display the first 500 characters of the response string.
        mTextView.setText("Response is: "+ response.substring(0,500));
    
, new Response.ErrorListener() 
    @Override
    public void onErrorResponse(VolleyError error) 
        mTextView.setText("That didn't work!");
    
);
// Add the request to the RequestQueue.
queue.add(stringRequest);

请求过程示意图：

取消Request
取消某一个请求我们可以直接调用request.cancle()方法，取消多个请求，可以采用以下方式：
初始化Request时，为其设置一个tag

public static final String TAG = "MyTag";
StringRequest stringRequest; // Assume this exists.
RequestQueue mRequestQueue;  // Assume this exists.
// Set the tag on the request.
stringRequest.setTag(TAG);
// Add the request to the RequestQueue.
mRequestQueue.add(stringRequest);

在Activity的onStop方法中,调用mRequestQueue.cancelAll(TAG)，可以取消所有标签为TAG的请求

@Override
protected void onStop () 
    super.onStop();
    if (mRequestQueue != null) 
        mRequestQueue.cancelAll(TAG);
    

自定义ResquestQueue

• DiskBasedCache，Volley缓存策略实现的核心组件
• BasicNetwork，Volley网络通信的核心组件
• Use androidHttpClient for apps targeting Android API levels lower than API Level 9 (Gingerbread). Prior to Gingerbread, HttpURLConnection was unreliable. For more discussion of this topic, see Android’s HTTP Clients.
• Use HttpURLConnection for apps targeting Android API Level 9 (Gingerbread) and higher.
• Use a Singleton Pattern

1.自定义Network

HttpStack stack;
// If the device is running a version >= Gingerbread...
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) 
    // ...use HttpURLConnection for stack.
 else 
    // ...use AndroidHttpClient for stack.

Network network = new BasicNetwork(stack);

2.自定义RequestQueue

RequestQueue mRequestQueue;
// Instantiate the cache
Cache cache = new DiskBasedCache(getCacheDir(), 1024 * 1024); // 1MB cap
// Set up the network to use HttpURLConnection as the HTTP client.
Network network = new BasicNetwork(new HurlStack());
// Instantiate the RequestQueue with the cache and network.
mRequestQueue = new RequestQueue(cache, network);
// Start the queue
mRequestQueue.start();
String url ="http://www.myurl.com";
// Formulate the request and handle the response.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
        new Response.Listener<String>() 
    @Override
    public void onResponse(String response) 
        // Do something with the response
    
,
    new Response.ErrorListener() 
        @Override
        public void onErrorResponse(VolleyError error) 
            // Handle error
    
);
// Add the request to the RequestQueue.
mRequestQueue.add(stringRequest);

3.使用单例模式管理RequestQueue的生命周期

private static MySingleton mInstance;
    private RequestQueue mRequestQueue;
    private ImageLoader mImageLoader;
    private static Context mCtx;
    private MySingleton(Context context) 
        mCtx = context;
        mRequestQueue = getRequestQueue();
        mImageLoader = new ImageLoader(mRequestQueue,
                new ImageLoader.ImageCache() 
            private final LruCache<String, Bitmap>
                    cache = new LruCache<String, Bitmap>(20);
            @Override
            public Bitmap getBitmap(String url) 
                return cache.get(url);
            
            @Override
            public void putBitmap(String url, Bitmap bitmap) 
                cache.put(url, bitmap);
            
        );
    
    public static synchronized MySingleton getInstance(Context context) 
        if (mInstance == null) 
            mInstance = new MySingleton(context);
        
        return mInstance;
    
    public RequestQueue getRequestQueue() 
        if (mRequestQueue == null) 
            // getApplicationContext() is key, it keeps you from leaking the
            // Activity or BroadcastReceiver if someone passes one in.
            mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
        
        return mRequestQueue;
    
    public <T> void addToRequestQueue(Request<T> req) 
        getRequestQueue().add(req);
    
    public ImageLoader getImageLoader() 
        return mImageLoader;
    

4.Client Use

// Get a RequestQueue
RequestQueue queue = MySingleton.getInstance(this.getApplicationContext()).
    getRequestQueue();
...
// Add a request (in this example, called stringRequest) to your RequestQueue.
MySingleton.getInstance(this).addToRequestQueue(stringRequest);

使用标准的请求

Volley支持的请求：

• StringRequest
• ImageRequest
• JsonObjectRequest and JsonArrayRequest

ImageRequest

• 可以异步地decode和resize图片，返回处理后的bitmap
• ImageLoader.管理图片请求，设置图片缓存，避免内存闪烁，响应的批量化返回(response coalescing)
• NetworkImageView.在视图离开后，自动取消视图上的请求

1.Use ImageRequest

ImageView mImageView;
String url = "http://i.imgur.com/7spzG.png";
mImageView = (ImageView) findViewById(R.id.myImage);
...
// Retrieves an image specified by the URL, displays it in the UI.
ImageRequest request = new ImageRequest(url,
    new Response.Listener() 
        @Override
        public void onResponse(Bitmap bitmap) 
            mImageView.setImageBitmap(bitmap);
        
    , 0, 0, null,
    new Response.ErrorListener() 
        public void onErrorResponse(VolleyError error) 
            mImageView.setImageResource(R.drawable.image_load_error);
        
    );
// Access the RequestQueue through your singleton class.
MySingleton.getInstance(this).addToRequestQueue(request);

2.Use ImageLoader and NetworkImageView

xml配置

<com.android.volley.toolbox.NetworkImageView
        android:id="@+id/networkImageView"
        android:layout_width="150dp"
        android:layout_height="170dp"
        android:layout_centerHorizontal="true" />

java代码

ImageLoader mImageLoader;
NetworkImageView mNetworkImageView;
private static final String IMAGE_URL =
    "http://developer.android.com/images/training/system-ui.png";
...
// Get the NetworkImageView that will display the image.
mNetworkImageView = (NetworkImageView) findViewById(R.id.networkImageView);
// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();
// Set the URL of the image that should be loaded into this view, and
// specify the ImageLoader that will be used to make the request.
mNetworkImageView.setImageUrl(IMAGE_URL, mImageLoader);

3.使用一般的ImageView

ImageLoader mImageLoader;
ImageView mImageView;
// The URL for the image that is being loaded.
private static final String IMAGE_URL =
    "http://developer.android.com/images/training/system-ui.png";
...
mImageView = (ImageView) findViewById(R.id.regularImageView);
// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();
mImageLoader.get(IMAGE_URL, ImageLoader.getImageListener(mImageView,
         R.drawable.def_image, R.drawable.err_image));

3.自定义ImageCache

The Volley toolbox provides a standard cache implementation via the DiskBasedCache class. This class caches files directly onto the hard disk in the specified directory. But to use ImageLoader, you should provide a custom in-memory LRU bitmap cache that implements the ImageLoader.ImageCache interface. You may want to set up your cache as a singleton

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
import android.util.DisplayMetrics;
import com.android.volley.toolbox.ImageLoader.ImageCache;
public class LruBitmapCache extends LruCache<String, Bitmap>
        implements ImageCache 
    public LruBitmapCache(int maxSize) 
        super(maxSize);
    
    public LruBitmapCache(Context ctx) 
        this(getCacheSize(ctx));
    
    @Override
    protected int sizeOf(String key, Bitmap value) 
        return value.getRowBytes() * value.getHeight();
    
    @Override
    public Bitmap getBitmap(String url) 
        return get(url);
    
    @Override
    public void putBitmap(String url, Bitmap bitmap) 
        put(url, bitmap);
    
    // Returns a cache size equal to approximately three screens worth of images.
    public static int getCacheSize(Context ctx) 
        final DisplayMetrics displayMetrics = ctx.getResources().
                getDisplayMetrics();
        final int screenWidth = displayMetrics.widthPixels;
        final int screenHeight = displayMetrics.heightPixels;
        // 4 bytes per pixel
        final int screenBytes = screenWidth * screenHeight * 4;
        return screenBytes * 3;
    

Request JSON

• JSONArrayRequest
• JSONObjectRequest

TextView mTxtDisplay;
ImageView mImageView;
mTxtDisplay = (TextView) findViewById(R.id.txtDisplay);
String url = "http://my-json-feed";
JsonObjectRequest jsObjRequest = new JsonObjectRequest
        (Request.Method.GET, url, null, new Response.Listener() 
    @Override
    public void onResponse(JSONObject response) 
        mTxtDisplay.setText("Response: " + response.toString());
    
, new Response.ErrorListener() 
    @Override
    public void onErrorResponse(VolleyError error) 
        // TODO Auto-generated method stub
    
);
// Access the RequestQueue through your singleton class.
MySingleton.getInstance(this).addToRequestQueue(jsObjRequest);

StringReuqest

前面已经介绍过，不再赘述

自定义Request

• 继承Request<T>, <T>代表返回的解析响应对象类型. 如果你的解析响应是字符串, 可以继承Request来创建自定义的String Request. 可以查看 StringRequest 和 ImageRequest 实现 Request的源代码.
• Implement the abstract methods parseNetworkResponse() and deliverResponse(), described in more detail below.

Example: GsonRequest

public class GsonRequest<T> extends Request<T> 
    private final Gson gson = new Gson();
    private final Class<T> clazz;
    private final Map<String, String> headers;
    private final Listener<T> listener;
    /**
     * Make a GET request and return a parsed object from JSON.
     *
     * @param url URL of the request to make
     * @param clazz Relevant class object, for Gson's reflection
     * @param headers Map of request headers
     */
    public GsonRequest(String url, Class<T> clazz, Map<String, String> headers,
            Listener<T> listener, ErrorListener errorListener) 
        super(Method.GET, url, errorListener);
        this.clazz = clazz;
        this.headers = headers;
        this.listener = listener;
    
    @Override
    public Map<String, String> getHeaders() throws AuthFailureError 
        return headers != null ? headers : super.getHeaders();
    
    @Override
    protected void deliverResponse(T response) 
        listener.onResponse(response);
    
    @Override
    protected Response<T> parseNetworkResponse(NetworkResponse response) 
        try 
            String json = new String(
                    response.data,
                    HttpHeaderParser.parseCharset(response.headers));
            return Response.success(
                    gson.fromJson(json, clazz),
                    HttpHeaderParser.parseCacheHeaders(response));
         catch (UnsupportedEncodingException e) 
            return Response.error(new ParseError(e));
         catch (JsonSyntaxException e) 
            //handle error
            return Response.error(new ParseError(e));
        
    

原文
Transmitting Network Data Using Volley