Android 解读Volley

来源：互联网发布：人性的枷锁知乎编辑：程序博客网时间：2024/05/01 08:57

之前有学过异步加载, 但由于是新到的一家公司上班, 要自己手动搭建一个新的框架, 很蛋疼, 朋友们推荐使用Volley 于是今天就测试爽了下, 表示还行..

不说废话, 直接上代码..

package com.example.testvolley;import org.json.JSONObject;import android.app.Activity;import android.app.ProgressDialog;import android.content.res.Resources.Theme;import android.os.Bundle;import com.android.volley.Request;import com.android.volley.RequestQueue;import com.android.volley.Response;import com.android.volley.VolleyError;import com.android.volley.toolbox.JsonObjectRequest;import com.android.volley.toolbox.Volley;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);getJson();}private void getJson() {RequestQueue queue = Volley.newRequestQueue(this);String jsonURL = "http://192.168.1.118:8000/Learning3/app/LoginAuth.action?username=admin&userpwd=123";final ProgressDialog progressDialog = ProgressDialog.show(this,"请稍后...", "正在加载...");try {Thread.sleep(2000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET,jsonURL, null, new Response.Listener<JSONObject>() { //返回来有数据的监听// 获取到的JSON的数据@Overridepublic void onResponse(JSONObject json) {if(progressDialog.isShowing()){progressDialog.dismiss();}String josnstr = json.toString();}}, new Response.ErrorListener() {  //返回的没有数据报错的监听@Overridepublic void onErrorResponse(VolleyError error) {System.out.println("error:" + error);}});queue.add(request); //这步是在队列里执行request请求..}}

效果还行.. 自己打印出Log看下就知道了...

然后分析下源码吧.. 我们都知道他是个异步线程加载的过程, 那么,, 这个异步的代码到底到哪里了?

上面的DEMO里的方法.. 是用add.. 于是LZ就杀到add 源码里去看.. 结果木有???? 什么情况????

    public Request add(Request request) {        // Tag the request as belonging to this queue and add it to the set of current requests.        request.setRequestQueue(this);        synchronized (mCurrentRequests) {            mCurrentRequests.add(request);        }        // Process requests in the order they are added.        request.setSequence(getSequenceNumber());        request.addMarker("add-to-queue");        // If the request is uncacheable, skip the cache queue and go straight to the network.        if (!request.shouldCache()) {            mNetworkQueue.add(request);            return request;        }        // Insert request into stage if there's already a request with the same cache key in flight.        synchronized (mWaitingRequests) {            String cacheKey = request.getCacheKey();            if (mWaitingRequests.containsKey(cacheKey)) {                // There is already a request in flight. Queue up.                Queue<Request> stagedRequests = mWaitingRequests.get(cacheKey);                if (stagedRequests == null) {                    stagedRequests = new LinkedList<Request>();                }                stagedRequests.add(request);                mWaitingRequests.put(cacheKey, stagedRequests);                if (VolleyLog.DEBUG) {                    VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", cacheKey);                }            } else {                // Insert 'null' queue for this cacheKey, indicating there is now a request in                // flight.                mWaitingRequests.put(cacheKey, null);                mCacheQueue.add(request);            }            return request;        }    }

这么长一段代码.. LZ 就这样蛋疼的看了一个下午的源码.. 把工作都丢一边了...

而且 add代码里面写了这么多.. 只是做了一个线程的同步与异步的控制, 并没有start()方法..

好吧.. 既然add方法没有, 那我们从第一个方法开始看吧

 public static RequestQueue newRequestQueue(Context context, HttpStack stack) {        File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);        String userAgent = "volley/0";        try {            String packageName = context.getPackageName();            PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);            userAgent = packageName + "/" + info.versionCode;        } catch (NameNotFoundException e) {        }        if (stack == null) {            if (Build.VERSION.SDK_INT >= 9) {                stack = new HurlStack();            } else {                // Prior to Gingerbread, HttpUrlConnection was unreliable.                // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html                stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));             }        }        Network network = new BasicNetwork(stack);        RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);        queue.start();   //<<<<<<<<<<<--------- 看!! 发现执行!!!!        return queue;    }

原来一开始他们就已经创建了一个等待请求的请求队列了!!!

根据包名+/加版本号.. 然后开启了一个新的Http客户端的栈的请求队列

到这里我们大概可以很肤浅的知道代码是在一开始就已经创建好一个栈等着结果进入..

然后在往下看..

Network network = new BasicNetwork(stack);

我们stack传进来的参数为空

    public BasicNetwork(HttpStack httpStack) {        // If a pool isn't passed in, then build a small default pool that will give us a lot of        // benefit and not use too much memory.        this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE));    }

由这步我们可以得知, 可能这里是要存放一个缓存池的一个数量

返回再往下执行看

    public RequestQueue(Cache cache, Network network, int threadPoolSize) {        this(cache, network, threadPoolSize,                new ExecutorDelivery(new Handler(Looper.getMainLooper())));    }

    public ExecutorDelivery(final Handler handler) {        // Make an Executor that just wraps the handler.        mResponsePoster = new Executor() {            @Override            public void execute(Runnable command) {                handler.post(command);            }        };    }

从这步我们可以得知, 要把前面NetWork的数据丢到线程里面了...

往下看执行..

    public void start() {        stop();  // Make sure any currently running dispatchers are stopped.        // Create the cache dispatcher and start it.        mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);        mCacheDispatcher.start();        // Create network dispatchers (and corresponding threads) up to the pool size.        for (int i = 0; i < mDispatchers.length; i++) {            NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,                    mCache, mDelivery);            mDispatchers[i] = networkDispatcher;            networkDispatcher.start();        }    }

public class CacheDispatcher extends Thread

闹了大半圈终于明白了...

整理下

首先Volley会创建一个等待的请求队列, 然后会开启一个Handler, 然后Handler 里所做的操作就是将当前线程post进去无限等待数据...(阻塞, 不懂的自己看Handler底层),

最后如果有请求进来, 就会去创建线程, 最后开启....蛋疼啊!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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