Android Volley同步请求无法正常工作

我试图使用RequestFuture向服务器发出同步请求,但它无法正常工作.使用异步完成时相同的请求工作正常.

这是我的代码:

 public void fetchModules(){
   JSONObject response = null;
    RequestQueue requestQueue = Volley.newRequestQueue(getContext());

    RequestFuture future = RequestFuture.newFuture();
    JsonObjectRequest request = new JsonObjectRequest(Url.ALL_MODULES_URL,null,future,future);
    requestQueue.add(request);


    try {
         response = future.get(3, TimeUnit.SECONDS); // Blocks for at most 10 seconds.
    } catch (InterruptedException e) {
             Log.d(TAG,"interupted");
     } catch (ExecutionException e) {
        Log.d(TAG,"execution");
    } catch (TimeoutException e) {
        e.printStackTrace();
    }

    Log.d(TAG,response.toString());
}

我得到一个nullpointerexception:

java.lang.NullPointerException:尝试在com.maths.app.AllModules.fetchModules(AllModules.java:85)的空对象引用上调用虚方法'java.lang.String org.json.JSONObject.toString()'在android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager)的android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)上的com.maths.app.AllModules.onCreateView(AllModules.java:51). java:1108)在android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)的android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)android.support.v4.app在Android.os的android.os.Handler.handleCallback(Handler.java:746)的android.support.v4.app.FragmentManagerImpl $ 1.run(FragmentManager.java:536)的.FragmentManagerImpl.execPendingActions(FragmentManager.java:1677) .Handler.dispatchMessage(Handler.java:95)位于android.app.Looper.loop(Looper.java:148)的android.app.ActivityThread.main(ActivityThread.java:5443),位于java.lang.reflect.Method.调用(娜 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:728)中的tive方法)

它返回一个null响应.我怎么解决这个问题？

TL;博士; 你被try-catch欺骗了

说明:因为RequestFuture.get()它可能正在UI线程上运行,所以你真的得到了一个java.util.concurrent.TimeoutException幕后.这是在主线程上执行调用时的默认行为.

try catch会阻止应用程序崩溃,但是当您尝试结果时,响应仍然是一个空引用会导致应用程序崩溃Log.如果您评论以下行,您将看到应用程序不再崩溃(那里).

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

修复:在另一个线程上调用RequestFuture网络!

一种方法:

    public class TestVolley {

    private String TAG = "SO_TEST";
    private String url = "http://pokeapi.co/api/v2/pokemon-form/1/";


    public JSONObject fetchModules(Context ctx){
        JSONObject response = null;
        RequestQueue requestQueue = Volley.newRequestQueue(ctx);


        RequestFuture future = RequestFuture.newFuture();
        JsonObjectRequest request = new JsonObjectRequest(url,null,future,future);
        requestQueue.add(request);


        try {
            response = future.get(3, TimeUnit.SECONDS); // Blocks for at most 10 seconds.
        } catch (InterruptedException e) {
            Log.d(TAG,"interrupted");
        } catch (ExecutionException e) {
            Log.d(TAG,"execution");
        } catch (TimeoutException e) {
            e.printStackTrace();
        }

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

        return response;
    }
}

在AsyncTask这将使网络调用:

public class MyVolleyAsyncTask extends AsyncTask {

    private Context ctx;

    public MyVolleyAsyncTask(Context hostContext)
    {
        ctx = hostContext;
    }

    @Override
    protected JSONObject doInBackground(String... params) {

        // Method runs on a separate thread, make all the network calls you need
        TestVolley tester = new TestVolley();

        return tester.fetchModules(ctx);
    }


    @Override
    protected void onPostExecute(JSONObject result)
    {
       // runs on the UI thread
       // do something with the result
    }
}

主要活动:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // this is your old code which will crash the app
        //TestVolley tester = new TestVolley();
        //tester.fetchModules(this);

        // Works!
        new MyVolleyAsyncTask(this).execute();
    }
}

结果:

com.so.henriquems.testvolleyfuture D/SO_TEST: {"id":1,"pokemon":{"url":"http:\/\/pokeapi.co\/api\/v2\/pokemon\/1\/","name":"bulbasaur"},[...]

希望这可以帮助

干杯!