Question

我正在接受以下异常

01-27 11:15:15.756  18348-18348/com.example.pnimje.newswipelistview E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
            at android.view.View.measure(View.java:15848)
            at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:728)
            at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:477)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:453)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2189)
            at android.view.View.measure(View.java:15848)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1905)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1284)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
            at android.view.Choreographer.doCallbacks(Choreographer.java:562)
            at android.view.Choreographer.doFrame(Choreographer.java:532)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
            at android.os.Handler.handleCallback(Handler.java:730)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)

和RecyclerView.java:1764是

    mLayout.onMeasure(mRecycler, mState, widthSpec, heightSpec);

为什么mLayout（LayoutManager）为空？

Answer 1

因为您尚未将LinearLayoutManager设置为RecyclerView。

例如：

    mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);
    LinearLayoutManager layoutManager = new LinearLayoutManager(context);
    mRecyclerView.setLayoutManager(layoutManager);
    mRecyclerView.setAdapter(new CustomAdapter());

Answer 2

这类错误通常源于未设置RecyclerView的布局管理器。贝因＆＃39;匆匆忙忙，我忘记设置一个以下错误结束：

java.lang.NullPointerException
        at android.support.v7.widget.RecyclerView.onInterceptTouchEvent(RecyclerView.java:1636)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1820)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2177)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1878)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2177)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1878)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2177)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1878)

以下行应该解决它：

mRecyclerView.setLayoutManager(new LinearLayoutManager((Activity)this));

Answer 3

Antón的反应很好，但在像我这样的初学者中可能会让人感到困惑，这可以澄清一些疑问。

RecyclerView rv;


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

    rv = (RecyclerView) findViewById(R.id.RecViewTest);
    LinearLayoutManager llm = new LinearLayoutManager(this);
    rv.setLayoutManager(llm);


}

Answer 4

您需要验证发送到适配器的内容不是空的List<Type>。我建议您按代码创建RecyclerView，稍后在获取信息时添加它，或者在将其传递给适配器的构造函数之前放置一个空的NULL对象。

NullPointerException的原因android.support.v7.widget.RecyclerView.onMeasure

4 个答案: