android – 在Fragment和FragmentStatePagerAdapter中使用ViewPager的片段导致异常(带完整示例)
作者:互联网
我有一个带有ViewPager的简单片段.
我正在使用最新的支持库,v4 rev18!
如果我第一次显示子片段,一切正常,如果我返回并再次显示它,应用程序崩溃时出现以下异常:
我有一个完整的例子显示,当发生以下异常时:
java.lang.NullPointerException
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:569)
at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1281)
at android.view.View.dispatchRestoreInstanceState(View.java:12043)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2688)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2694)
at android.view.View.restoreHierarchyState(View.java:12021)
at android.support.v4.app.Fragment.restoreViewState(Fragment.java:425)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:949)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4800)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
at dalvik.system.NativeStart.main(Native Method)
我能够以其他方式在子片段中使用ViewPager,但如果我手动添加/删除子片段并在子片段中使用FragmentStatePagerAdapter,我就无法使用它…
以下示例应该可以工作,但它没有…我已经添加了一些解决了一些问题的代码,但它并没有解决所有问题……
import java.lang.reflect.Field;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.TextView;
public class TestActivity extends FragmentActivity implements OnClickListener
{
private Fragment fragment1;
private Fragment fragment2;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.test_main);
fragment1 = getSupportFragmentManager().findFragmentByTag("fragment1");
fragment2 = getSupportFragmentManager().findFragmentByTag("fragment2");
}
@Override
public void onClick(View v)
{
Fragment nextFragment = null;
String nextFragmentTag = null;
if (v.getId() == R.id.button1)
{
if (fragment1 == null)
fragment1 = ContainerFragment.newInstance(1);
nextFragment = fragment1;
nextFragmentTag = "fragment1";
}
else if (v.getId() == R.id.button2)
{
if (fragment2 == null)
fragment2 = ContainerFragment.newInstance(2);
nextFragment = fragment2;
nextFragmentTag = "fragment2";
}
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main, nextFragment, nextFragmentTag);
transaction.addToBackStack(null);
transaction.commit();
}
public static class MainPagerAdapter extends FragmentStatePagerAdapter
{
public int button;
public MainPagerAdapter(FragmentManager fm)
{
super(fm);
}
@Override
public Fragment getItem(int i)
{
return SubFragment.newInstance(button, i);
}
@Override
public int getCount()
{
return 10;
}
}
public static class ContainerFragment extends Fragment
{
static ContainerFragment newInstance(int pos)
{
ContainerFragment f = new ContainerFragment();
Bundle args = new Bundle();
args.putInt("pos", pos);
f.setArguments(args);
return f;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
View rootView = inflater.inflate(R.layout.view_pager, container, false);
ViewPager pager = (ViewPager) rootView.findViewById(R.id.pager);
MainPagerAdapter adapter = new MainPagerAdapter(getChildFragmentManager());
adapter.button = getArguments().getInt("pos");
pager.setAdapter(adapter);
return rootView;
}
// ---------------------------------------------------------------
// HACK FIX für java.lang.IllegalStateException: No activity
// ---------------------------------------------------------------
private static final Field sChildFragmentManagerField;
static
{
Field f = null;
try
{
f = android.support.v4.app.Fragment.class.getDeclaredField("mChildFragmentManager");
f.setAccessible(true);
}
catch (NoSuchFieldException e)
{
}
sChildFragmentManagerField = f;
}
@Override
public void onDetach()
{
super.onDetach();
if (sChildFragmentManagerField != null)
{
try
{
sChildFragmentManagerField.set(this, null);
}
catch (Exception e)
{
}
}
}
}
public static class SubFragment extends Fragment
{
static SubFragment newInstance(int button, int pos)
{
SubFragment f = new SubFragment();
Bundle args = new Bundle();
args.putString("key", "Button " + button + "Fragment " + pos);
f.setArguments(args);
return f;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
View rootView = inflater.inflate(R.layout.test_subfragment, container, false);
((TextView) rootView.findViewById(R.id.tv1)).setText(getArguments().getString("key"));
return rootView;
}
}
}
为了完整起见,我还添加了xml文件:
test_main.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/main"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onClick"
android:text="Button1" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onClick"
android:text="Button2" />
</LinearLayout>
</FrameLayout>
test_subfragment.xml
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/tv1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:textSize="50sp" />
view_pager.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/llContainer"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
解决方法:
将另一个FrameLayout添加到主活动的布局中.这是你放置片段的地方.
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/main"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onClick"
android:text="Button1" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onClick"
android:text="Button2" />
<!-- add this -->
<FrameLayout
android:id="@+id/fragment_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</FrameLayout>
</LinearLayout>
</FrameLayout>
由于您要将碎片添加到BackStack,因此无需保存它们的实例.这就是你应用程序崩溃的原因.调整onClick()方法,如下所示:
@Override
public void onClick(View v)
{
Fragment nextFragment = null;
String nextFragmentTag = null;
if (v.getId() == R.id.button1)
{
nextFragment = ContainerFragment.newInstance(1);
nextFragmentTag = "fragment1";
}
else if (v.getId() == R.id.button2)
{
nextFragment = ContainerFragment.newInstance(2);
nextFragmentTag = "fragment2";
}
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragment_frame, nextFragment, nextFragmentTag);
transaction.addToBackStack(null);
transaction.commit();
}
I tested the code. Changing the Fragments with the buttons works, and
the state the ViewPager was left when returing to it is preserved.
标签:fragmentmanager,android,android-fragments,android-viewpager,android-support-libr 来源: https://codeday.me/bug/20191008/1870084.html