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android - java.lang.Class java.lang.Object.getClass()' 在空对象引用上

转载 作者:IT老高 更新时间:2023-10-28 23:02:33 29 4
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我尝试将 viewPager 与 tablayout 一起使用,但是当我使用 view pager 设置适配器时,我收到错误“java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass () 在空对象引用上”我不明白为什么会显示此错误。

查看寻呼机设置适配器:

viewPager= (ViewPager) findViewById(R.id.viewPager_id);
viewPager.setAdapter(newViewPagerAdapterUseThisClass(getSupportFragmentManager(),14));

适配器类:

class ViewPagerAdapterUseThisClass extends FragmentPagerAdapter {
int countTabItem;
ViewPagerAdapterUseThisClass(FragmentManager fm,int contTabItem) {
super(fm);

this.countTabItem=contTabItem;
}

@Override
public Fragment getItem(int position) {

if(position==0){
EnthusamTab enthusamTab=new EnthusamTab();
return enthusamTab;
}

return null;
}

@Override
public int getCount() {
return countTabItem;
}
}

查看寻呼机 xml 文件:

 <android.support.v4.view.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/tab_layout_id"
android:id="@+id/viewPager_id"/>

错误日志:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:380)
at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:375)
at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:103)
at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1034)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1248)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
at android.view.View.measure(View.java:19861)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:19861)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1081)
at android.view.View.measure(View.java:19861)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:19861)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
at android.view.View.measure(View.java:19861)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:19861)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
at android.view.View.measure(View.java:19861)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689)
at android.view.View.measure(View.java:19861)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1619)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6343)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
at android.view.Choreographer.doCallbacks(Choreographer.java:686)
at android.view.Choreographer.doFrame(Choreographer.java:621)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6126)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

最佳答案

当您在 PagerAdaptergetItem(int position) 方法返回 null 时会发生此异常。

您必须在 getCount() 方法中设置返回值(n),并在 getItem(int position) 方法中返回 Fragment对于所有 (0 .. n-1) 个位置。

例如,如果您从 getCount() 方法返回 3,那么您必须为 的位置 0、1 和 2 返回一个非空 Fragment getItem(int position) 方法。如果您为位置 0、1 或 2 返回 null,您将得到:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference

private static class MyPagerAdapter extends FragmentPagerAdapter {
...

@Override
public int getCount() {
return 3;
}

@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new XFragment();
case 1:
return new YFragment();
case 2:
return new ZFragment();
default:
return null; // Problem occurs at this condition!
}
}
}

关于android - java.lang.Class java.lang.Object.getClass()' 在空对象引用上,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41826639/

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