今天debug別人的代碼，碰到這麼個錯誤：
05-29 20:27:51.665: E/AndroidRuntime(27611): java.lang.NullPointerException
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.support.v4.widget.SwipeRefreshLayout.onMeasure(SwipeRefreshLayout.java:559)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
05-29 20:27:51.665: E/AndroidRuntime(27611): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.View.measure(View.java:16508)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1955)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1152)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1334)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1039)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5648)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.Choreographer.doCallbacks(Choreographer.java:574)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.Choreographer.doFrame(Choreographer.java:544)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.os.Handler.handleCallback(Handler.java:733)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.os.Handler.dispatchMessage(Handler.java:95)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.os.Looper.loop(Looper.java:136)
05-29 20:27:51.665: E/AndroidRuntime(27611): at android.app.ActivityThread.main(ActivityThread.java:5047)
05-29 20:27:51.665: E/AndroidRuntime(27611): at java.lang.reflect.Method.invokeNative(Native Method)
05-29 20:27:51.665: E/AndroidRuntime(27611): at java.lang.reflect.Method.invoke(Method.java:515)
05-29 20:27:51.665: E/AndroidRuntime(27611): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:806)
05-29 20:27:51.665: E/AndroidRuntime(27611): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
05-29 20:27:51.665: E/AndroidRuntime(27611): at dalvik.system.NativeStart.main(Native Meth
網上查了查，碰到的類似的錯誤不是很多，再次記錄一下。
RecyclerView在onCreate的時候，要確定尺寸，需要執行：
RecyclerView.setLayoutManager(new LinearLayoutManager(mContext));
而我遇到的問題的原因是：
setLayoutManager這個方法執行時間在一個網絡訪問得到結果之後，所以纔出現上面的問題。