Question

在我的项目中，我正在使用volley下载一个JSON流，我将其解析并显示在列表视图中。我使用以下方法加载我的数据：

private void loadEventData(int year, final int month) {

    // get volley request queue
    requestQueue = cpcApplication.getRequestQueue(getActivity());

    String url = "****************?year=" + year
            + "&month=" + month;

    pd = ProgressDialog.show(getActivity(), "Loading Events", "Retrieving Data from Server");
    pd.setCancelable(true);

    JsonObjectRequest jr = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {

        @Override
        public void onResponse(JSONObject response) {

            Log.i(TAG, response.toString());

            // parse the incoming response
            parseJson(response, month);

            // notify the listview that the data set has changed
            adapter.notifyDataSetChanged();

            // set the listview at the top position
            listView.setSelection(current.get(Calendar.DAY_OF_MONTH));

            // dismiss the ProgressDialog
            pd.dismiss();

        }
        }, new Response.ErrorListener() {

        @Override
        public void onErrorResponse(VolleyError error) {

            error.printStackTrace();

            // cancel the progress dialog
            pd.dismiss();

            // let the user know that a network connection is not available
            Toast.makeText(getActivity(), "Cannot communicate with server.  Check network connection.", Toast.LENGTH_LONG).show();
        }

    });

    // add the network request to the queue
    requestQueue.add(jr);

}

第一次调用此方法非常有效。在第二次调用中，我收到超时错误。当我使用以下命令时：

jr.setRetryPolicy(new DefaultRetryPolicy(
            2500, DefaultRetryPolicy.DEFAULT_TIMEOUT_MS, DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

为了增加请求的时间，请求需要30秒以上并产生以下日志输出：

10-19 20:53:19.746: D/Volley(17523): [2786] BasicNetwork.logSlowRequests: HTTP response for request=<[ ] http://************ 0x63ea5535 NORMAL 1> [lifetime=41769], [size=5467846], [rc=200], [retryCount=2]
10-19 20:53:19.796: D/dalvikvm(17523): GC_CONCURRENT freed 7462K, 26% free 24424K/33000K, paused 6ms+4ms, total 56ms
10-19 20:53:19.796: D/dalvikvm(17523): WAIT_FOR_CONCURRENT_GC blocked 51ms
10-19 20:53:19.826: I/dalvikvm-heap(17523): Grow heap (frag case) to 35.123MB for 10935708-byte allocation
10-19 20:53:19.857: D/dalvikvm(17523): GC_FOR_ALLOC freed 3K, 20% free 35100K/43680K, paused 23ms, total 28ms
10-19 20:53:19.917: D/dalvikvm(17523): GC_CONCURRENT freed 2018K, 19% free 35816K/43680K, paused 3ms+4ms, total 60ms
10-19 20:53:20.007: D/dalvikvm(17523): GC_CONCURRENT freed 4874K, 15% free 37226K/43680K, paused 2ms+3ms, total 27ms
10-19 20:53:20.007: D/dalvikvm(17523): WAIT_FOR_CONCURRENT_GC blocked 24ms
10-19 20:53:20.067: D/dalvikvm(17523): GC_FOR_ALLOC freed 5037K, 15% free 38601K/44900K, paused 19ms, total 19ms
10-19 20:53:20.117: D/dalvikvm(17523): GC_FOR_ALLOC freed 4680K, 14% free 40045K/46564K, paused 20ms, total 20ms
10-19 20:53:20.177: D/dalvikvm(17523): GC_FOR_ALLOC freed 5576K, 14% free 41572K/48272K, paused 20ms, total 20ms
10-19 20:53:20.227: D/dalvikvm(17523): GC_FOR_ALLOC freed 6133K, 15% free 43406K/50548K, paused 20ms, total 20ms
10-19 20:53:20.287: D/dalvikvm(17523): GC_CONCURRENT freed 6486K, 15% free 45029K/52428K, paused 2ms+2ms, total 24ms
10-19 20:53:20.287: D/dalvikvm(17523): WAIT_FOR_CONCURRENT_GC blocked 11ms
10-19 20:53:20.407: D/Volley(17523): [1] Request.finish: 42553 ms: [ ] http://****** 0x63ea5535 NORMAL 1

当我在浏览器中执行相同的请求时，只需几秒钟。为什么延迟和令人难以置信的内存消耗？

Answer 1

对您创建新RequestQueue的方法的每次调用都不是推荐的方法。您应该创建一个RequestQueue，可能是在创建应用时初始化一次的公开可见单例。

尝试将RequestQueue移到外面，看看它是否能解决您的问题。

Answer 2

我遇到了一些问题：

Volley.newRequestQueue(getApplicationContext());

它导致启动时的第一个请求在某些手机中花费了很长时间。我改为：

Cache cache = new DiskBasedCache(getCacheDir(), 1024 * 1024);
Network network = new BasicNetwork(new HurlStack());
mRequestQueue = new RequestQueue(cache, network);
mRequestQueue.start();

这解决了我的问题。

Answer 3

我正在尝试解释几个代码（已经简要解释了Itai）

下面的代码解释了如何将Volley的全局请求队列与应用程序类的单例实例一起使用，以便在其他地方轻松访问，并使代码更具内存效率！

public class ApplicationController扩展Application {

/**
 * Log or request TAG
 */
public static final String TAG = "VolleyPatterns";

/**
 * Global request queue for Volley
 */
private RequestQueue mRequestQueue;

/**
 * A singleton instance of the application class for easy access in other places
 */
private static ApplicationController sInstance;

@Override
public void onCreate() {
    super.onCreate();

    // initialize the singleton
    sInstance = this;
}

/**
 * @return ApplicationController singleton instance
 */
public static synchronized ApplicationController getInstance() {
    return sInstance;
}

/**
 * @return The Volley Request queue, the queue will be created if it is null
 */
public RequestQueue getRequestQueue() {
    // lazy initialize the request queue, the queue instance will be
    // created when it is accessed for the first time
    if (mRequestQueue == null) {
        mRequestQueue = Volley.newRequestQueue(getApplicationContext());
    }

    return mRequestQueue;
}

/**
 * Adds the specified request to the global queue, if tag is specified
 * then it is used else Default TAG is used.
 * 
 * @param req
 * @param tag
 */
public <T> void addToRequestQueue(Request<T> req, String tag) {
    // set the default tag if tag is empty
    req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);

    VolleyLog.d("Adding request to queue: %s", req.getUrl());

    getRequestQueue().add(req);
}

/**
 * Adds the specified request to the global queue using the Default TAG.
 * 
 * @param req
 * @param tag
 */
public <T> void addToRequestQueue(Request<T> req) {
    // set the default tag if tag is empty
    req.setTag(TAG);

    getRequestQueue().add(req);
}

/**
 * Cancels all pending requests by the specified TAG, it is important
 * to specify a TAG so that the pending/ongoing requests can be cancelled.
 * 
 * @param tag
 */
public void cancelPendingRequests(Object tag) {
    if (mRequestQueue != null) {
        mRequestQueue.cancelAll(tag);
    }
} }

完整实施参考此blog

致谢：Arnab Chakraborty

排球缓慢并导致内存泄漏

3 个答案: