Java 如何在PageViewer中显示3个片段
在一个片段中,我试图创建一个包含3个片段的ViewPager,您可以在它们之间滑动。 4.我在理解结构和所犯的错误方面遇到了困难Java 如何在PageViewer中显示3个片段,java,android,android-fragments,Java,Android,Android Fragments,在一个片段中,我试图创建一个包含3个片段的ViewPager,您可以在它们之间滑动。 4.我在理解结构和所犯的错误方面遇到了困难 public class ContactFragment extends Fragment { FragmentPagerAdapter adapterViewPager; private FragmentActivity myContext; @Override public View onCreateView(LayoutInflater inflater,
public class ContactFragment extends Fragment {
FragmentPagerAdapter adapterViewPager;
private FragmentActivity myContext;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.view_pager, container, false);
ViewPager vpPager = (ViewPager) rootView.findViewById(R.id.vpPager);
adapterViewPager = new MyPagerAdapter(myContext.getSupportFragmentManager());
vpPager.setAdapter(adapterViewPager);
return rootView;
}
@Override
public void onAttach(Activity activity) {
myContext=(FragmentActivity) activity;
super.onAttach(activity);
}
public static class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 3;
public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
}
// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}
// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return FirstFragment.newInstance(0, "Page # 1");
case 1: // Fragment # 0 - This will show FirstFragment different title
return FirstFragment.newInstance(1, "Page # 2");
default:
return null;
}
}
// Returns the page title for the top indicator
@Override
public CharSequence getPageTitle(int position) {
return "Page " + position;
}
}
}
我的ViewPager布局xml如下所示:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.view.ViewPager
android:id="@+id/vpPager"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v4.view.PagerTabStrip
android:id="@+id/pager_header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="top"
android:paddingBottom="4dp"
android:paddingTop="4dp" />
</android.support.v4.view.ViewPager>
</LinearLayout>
当我运行应用程序并加载片段时,它看起来是正确的,但当我尝试在pageviewer中滑动到新片段时,它崩溃了:
E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: org.example.magnusluca.drawertestapp, PID: 3624
java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference
用这个
@Override
public Fragment getItem(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return FirstFragment.newInstance(0, "Page # 1");
case 1: // Fragment # 0 - This will show FirstFragment different title
return FirstFragment.newInstance(1, "Page # 2");
case 2:
return FirstFragment.newInstance(2, "Page # 3");
default:
return new Fragment();
}
}
您应该有3个开关盒,并且您的默认盒不应返回null谢谢!但我不确定为什么会用无效的位置调用getItem?因为我们有一个getCount()来保护位置值,对吗?
@Override
public Fragment getItem(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return FirstFragment.newInstance(0, "Page # 1");
case 1: // Fragment # 0 - This will show FirstFragment different title
return FirstFragment.newInstance(1, "Page # 2");
case 2:
return FirstFragment.newInstance(2, "Page # 3");
default:
return new Fragment();
}
}