我正在尝试在我的Android应用中进行一些网络连接。
导致我的错误的事件序列如下：
在我的片段中，如果还没有，我会获得我的VolleySingleton类的新实例。
public static VolleySingleton getInstance() {
if (vInstance == null) {
vInstance = new VolleySingleton();
}
return vInstance;
}
在创建VolleySingleton的实例时，我创建了一个请求队列并将其设置为等于Volley.newRequestQueue（myApplication.getContext（））;
public class VolleySingleton {
private static VolleySingleton sInstance = null;
private ImageLoader imageLoader;
private RequestQueue mRequestQueue;
MyApplication myApplication = new MyApplication();
private VolleySingleton() {
mRequestQueue = Volley.newRequestQueue(myApplication.getAppContext());
imageLoader = new ImageLoader(mRequestQueue, new ImageLoader.ImageCache() {
private LruCache<String, Bitmap> cache = new LruCache<>((int)(Runtime.getRuntime().maxMemory()/1024/8));
@Override
public Bitmap getBitmap(String url) {
return cache.get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
cache.put(url, bitmap);
}
});
}
public static VolleySingleton getInstance() {
if (sInstance == null) {
sInstance = new VolleySingleton();
}
return sInstance;
}
public RequestQueue getRequestQueue() {
return mRequestQueue;
}
public ImageLoader getImageLoader() {
return imageLoader;
}
}
现在，myApplication只是扩展Application的MyApplication类的一个实例，而getContext（）只是在MyApplication的实例上调用getApplicationContext。以下是MyApplication类的代码：
public class MyApplication extends Application {
private static MyApplication sInstance;
public static final String API_KEY = "xxxxxxxx";
@Override
public void onCreate() {
super.onCreate();
sInstance=this;
}
public static MyApplication getInstance() {
return sInstance;
}
public Context getAppContext() {
return sInstance.getApplicationContext();
}
}
当我尝试return sInstance.getApplicationContext();
我已经设法让相同的代码在一个单独的测试项目中工作，所以我在这里不知所措。
这是我的logcat：
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context com.xxxxxxxxx.chessgame.Models.MyApplication.getApplicationContext()' on a null object reference
at com.xxxxxxxxx.chessgame.Models.MyApplication.getAppContext(MyApplication.java:28)
at com.xxxxxxxxxx.chessgame.Networking.VolleySingleton.<init>(VolleySingleton.java:25)
at com.xxxxxxxxx.chessgame.Networking.VolleySingleton.getInstance(VolleySingleton.java:42)
at com.xxxxxxxx.chessgame.RecyclerViews.FragmentViewOne.onCreate(FragmentViewOne.java:95)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1763)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:913)
at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:842)
at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:859)
at android.support.v4.app.FragmentStatePagerAdapter.setPrimaryItem(FragmentStatePagerAdapter.java:152)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1071)
at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
at android.view.View.measure(View.java:17430)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:851)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
at android.view.View.measure(View.java:17430)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.Act
答案 0 :(得分：5)
请确保您已将清单中的MyApplication类声明为 android：name =＆＃34; packagename.MyApplication＆＃34; 应用程序标记
答案 1 :(得分：2)
MyApplication myApplication = new MyApplication（）;
似乎错了。
您可以更改VolleySingleton的构造函数和getInstance方法以接受Context作为参数。
Application有onCreate方法表明，它的生命周期是由Android操作系统管理的。你不应该直接调用构造函数，就像你不应该做新的Activity（）一样。 您可以从例如获取应用程序的实例Activity#getApplicationContext()