片段中帶有setText的NullpointerException（Android）

Question

我有一個使用滾動選項卡在各個片段之間的應用程序。 每個片段僅顯示預設文本。 文本將被格式化以具有良好的外觀，因此我需要使用html解析器來使其正確顯示。 我對Java和android非常陌生，所以我認為我的布局可能有誤，但是我對此感到困惑，我希望有人能提供幫助！ 該應用在啟動時崩潰。 該字符串存在於字符串文件中。

這是片段：

public static class AboutMeFragment extends Fragment {

    public AboutMeFragment() {
    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         textviewabout = (TextView)getActivity().findViewById(R.id.textviewabout);
         textviewabout.setText(Html.fromHtml(getString(R.string.about_me)));
        View rootView = inflater.inflate(R.layout.aboutme,
                container, false);
        return rootView;
    }
}

這（再次，很確定這是不正確的）創建了textview。

public class MainActivity extends FragmentActivity {

 SectionsPagerAdapter mSectionsPagerAdapter;

 ViewPager mViewPager;
 static TextView textviewabout;

這是aboutme.xml

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:id="@+id/textviewabout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="10dp"
        android:layout_marginTop="10dp"
        android:scrollbars = "vertical"
        android:text="@string/about_me" />
     </ScrollView>

這是日志貓：

03-15 18:38:11.332: E/Trace(30586): error opening trace file: No such file or directory (2)
03-15 18:38:11.722: W/dalvikvm(30586): threadid=1: thread exiting with uncaught exception (group=0x41094540)
03-15 18:38:11.802: E/AndroidRuntime(30586): FATAL EXCEPTION: main
03-15 18:38:11.802: E/AndroidRuntime(30586): java.lang.NullPointerException
03-15 18:38:11.802: E/AndroidRuntime(30586):    at com.example.keiththomsonsicv.MainActivity$AboutMeFragment.onCreateView(MainActivity.java:142)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.View.measure(View.java:15286)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4832)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.View.measure(View.java:15286)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.View.measure(View.java:15286)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4832)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2230)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.View.measure(View.java:15286)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2105)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1262)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1492)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1160)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4682)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:738)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.Choreographer.doCallbacks(Choreographer.java:564)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.Choreographer.doFrame(Choreographer.java:532)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:723)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.os.Handler.handleCallback(Handler.java:615)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.os.Handler.dispatchMessage(Handler.java:92)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.os.Looper.loop(Looper.java:155)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at android.app.ActivityThread.main(ActivityThread.java:5520)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at java.lang.reflect.Method.invokeNative(Native Method)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at java.lang.reflect.Method.invoke(Method.java:511)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
03-15 18:38:11.802: E/AndroidRuntime(30586):    at dalvik.system.NativeStart.main(Native Method)

關於me.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$AboutMeFragment" >
<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:id="@+id/textviewabout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="10dp"
        android:layout_marginTop="10dp"
        android:scrollbars = "vertical"
        android:text="textviewabout" />
     </ScrollView>

</RelativeLayout>

Answer 1

如果從LogCat提供Stacktrace，發現錯誤會更容易，但是我看到一個明顯的錯誤：

在您的Fragment中，您指的是Activity以獲取TextView，但是您的textviewabout肯定是您的片段的一部分，因此我確定代碼必須是

public static class AboutMeFragment extends Fragment {

     public AboutMeFragment() {
     }

     @Override

     public View onCreateView(LayoutInflater inflater, ViewGroup container,
             Bundle savedInstanceState) {
          View rootView = inflater.inflate(R.layout.aboutme,
            container, false);
          textviewabout = (TextView)rootView.findViewById(R.id.textviewabout);
          textviewabout.setText(Html.fromHtml(getString(R.string.about_me)));
          return rootView;
     }
}

編輯：在您的活動中，您僅顯示聲明，而沒有代碼顯示片段的方式。 您應該添加Activity的XML以顯示是否在其中聲明了Fragment。

Answer 2

您應該初始化視圖並在Fragment onActivityCreated中調用setText 。 因為您的視圖可能還沒有准備好。

Answer 3

在我看來，您的textviewabout對象為null（也許您可以通過調試應用程序來確認）。

您如何告訴您的Activity使用aboutme.xml作為布局？ 您是否真的打算將此布局用於活動，或者是否要將其用於片段ui？

如果您想將其用於片段，則必須使用充氣機，您可以使用onCreateView方法首先為aboutme.xml布局充氣，然后再檢索TextView（並且您可能希望將TextView放在Fragment類中，在任何普通的szenario中都不需要靜態視圖類）

問候，托馬斯