为什么我让我的RecyclerView空引用 [英] Why am I getting a null reference on my RecyclerView
问题描述
我想用RecyclerView在我的片段。它显示了罚款的第一个选项卡,但是当我刷到第二个选项卡,然后回到第一个我得到以下错误:
显示java.lang.NullPointerException:尝试调用虚拟方法无效 android.support.v7.widget.RecyclerView $ LayoutManager.stopSmoothScroller()' 在一个空对象引用
有谁知道为什么我会得到这个错误?它似乎有一个电话,我在我的片段切换很想念,但我不明白。
寻呼机适配器片段:
公共类PagerAdapter扩展FragmentPagerAdapter {
私人最终的String []业权= {头0,标题1};
公共PagerAdapter(FragmentManager FM){
超(FM);
}
@覆盖
公共CharSequence的getPageTitle(INT位置){
返回TITLES [位置]
}
@覆盖
公众诠释getCount将(){
返回TITLES.length;
}
@覆盖
公共片段的getItem(INT位置){
开关(位置){
情况下0:
返回新FragmentOne();
情况1:
返回新FragmentTwo();
默认:
返回新FragmentOne();
}
}
}
FragmentOne和放大器; FragmentTwo使用我创建了一个样板类:
公共类FragmentOne扩展基地{
... code在RecyclerView显示内容。只包含我的自定义适配器的RecyclerView ...
}
文章:
公共抽象类中相应扩展片段{
公众查看MView的;
公共RecyclerView mDataView;
公共进度mProgressBar;
公共语境mContext;
私人RecyclerView.LayoutManager mLayoutManager;
公共基地(){}
@覆盖
公共查看onCreateView(LayoutInflater _i,ViewGroup中_vg,捆绑savedInstanceBundle){
MVIEW = _i.inflate(R.layout.f_base,NULL);
mDataView =(RecyclerView)mView.findViewById(R.id.data);
mProgressBar =(进度)mView.findViewById(R.id.loading);
mLayoutManager =新LinearLayoutManager(mContext);
mDataView.setLayoutManager(mLayoutManager);
mContext = this.getActivity();
返回MView的;
}
@覆盖
公共无效的OnStart(){
super.onStart();
在里面();
做工作();
}
公共抽象无效的init();
公共抽象无效的doWork();
}
修改
错误堆栈跟踪:
十二月11日至2号:49:44.171 3708-3708 / com.nitrox.digitune E / AndroidRuntime:致命异常:主要
工艺:com.nitrox.digitune,PID:3708
显示java.lang.NullPointerException:尝试调用虚拟方法无效android.support.v7.widget.RecyclerView $ LayoutManager.stopSmoothScroller()'对空对象引用
在android.support.v7.widget.RecyclerView.stopScrollersInternal(RecyclerView.java:1159)
在android.support.v7.widget.RecyclerView.stopScroll(RecyclerView.java:1151)
在android.support.v7.widget.RecyclerView.onDetachedFromWindow(RecyclerView.java:1356)
在android.view.View.dispatchDetachedFromWindow(View.java:13441)
在android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2837)
在android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
在android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
在android.view.ViewGroup.removeViewInternal(ViewGroup.java:4163)
在android.view.ViewGroup.removeViewInternal(ViewGroup.java:4136)
在android.view.ViewGroup.removeView(ViewGroup.java:4068)
在android.support.v4.view.ViewPager.removeView(ViewPager.java:1326)
在android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1045)
在android.support.v4.app.FragmentManagerImpl.detachFragment(FragmentManager.java:1280)
在android.support.v4.app.BackStackRecord.run(BackStackRecord.java:724)
在android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
在android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
在android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
在android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
在android.support.v4.view.ViewPager.populate(ViewPager.java:919)
在android.support.v4.view.ViewPager $ 3.run(ViewPager.java:249)
在android.view.Choreographer $ CallbackRecord.run(Choreographer.java:767)
在android.view.Choreographer.doCallbacks(Choreographer.java:580)
在android.view.Choreographer.doFrame(Choreographer.java:549)
在android.view.Choreographer $ FrameDisplayEventReceiver.run(Choreographer.java:753)
在android.os.Handler.handleCallback(Handler.java:739)
在android.os.Handler.dispatchMessage(Handler.java:95)
在android.os.Looper.loop(Looper.java:135)
在android.app.ActivityThread.main(ActivityThread.java:5221)
在java.lang.reflect.Method.invoke(本机方法)
在java.lang.reflect.Method.invoke(Method.java:372)
在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:899)
在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
基本上,你的LayoutManager是被布置在你的回收站已经完成它的。
从Android源:
@覆盖
保护无效onDetachedFromWindow(){
super.onDetachedFromWindow();
如果(mItemAnimator!= NULL){
mItemAnimator.endAnimations();
}
mFirstLayoutComplete = FALSE;
stopScroll();
mIsAttached = FALSE;
如果(mLayout!= NULL){
mLayout.onDetachedFromWindow(这一点,mRecycler);
}
removeCallbacks(mItemAnimatorRunner);
}
问题是stopScroll试图调用mLayout.stopSmoothScroller();任何检查mLayout为空。我扔togeather一个非常哈克热修复程序的应用程序,我一直在工作,但不应该被用来作为一个长期的解决方案,因为它是非常一个黑客,但我有一个时间紧迫,所以我不得不赶上空指针异常。我剪了我的处理程序,因为它是应用特定的。
我烫只是创造延长RecyclerView的自定义视图:
进口android.content.Context;
进口android.support.v7.widget.RecyclerView;
进口android.util.AttributeSet;
公共类HotFixRecyclerView扩展RecyclerView
{
公共HotFixRecyclerView(上下文的背景下)
{
超(上下文);
}
公共HotFixRecyclerView(上下文的背景下,ATTRS的AttributeSet)
{
超(背景下,ATTRS);
}
公共HotFixRecyclerView(上下文的背景下,ATTRS的AttributeSet,INT defStyle)
{
超(背景下,ATTRS,defStyle);
}
@覆盖
公共无效stopScroll()
{
尝试
{
super.stopScroll();
}
赶上(NullPointerException异常除外)
{
/ **
*本mLayout已前的处置
* RecyclerView这停止应用程序
*崩溃。
* /
}
}
}
然后切换到我自己的看法到RecyclerView所有引用。如果你使用它,请删除它,一旦机器人已经修补了这个问题,因为它是一个黑客攻击的一位。
I am trying to use the RecyclerView in my fragments. It shows up fine for the first tab, but when I swipe to the second tab and then back to the first one I get the following error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.stopSmoothScroller()' on a null object reference
Does anyone know why I would be getting this error? It seems that there is a call that I'm missing before I the fragments switch, but I can't figure it out.
Pager Adapter for Fragments:
public class PagerAdapter extends FragmentPagerAdapter {
private final String[] TITLES = {"Header 0", "Header 1" };
public PagerAdapter(FragmentManager fm){
super(fm);
}
@Override
public CharSequence getPageTitle(int position){
return TITLES[position];
}
@Override
public int getCount() {
return TITLES.length;
}
@Override
public Fragment getItem(int position){
switch(position){
case 0:
return new FragmentOne();
case 1:
return new FragmentTwo();
default:
return new FragmentOne();
}
}
}
FragmentOne & FragmentTwo use a boilerplate class I created:
public class FragmentOne extends Base {
... code for displaying content in the RecyclerView. Just contains my custom Adapter for the RecyclerView ...
}
Base:
public abstract class Base extends Fragment {
public View mView;
public RecyclerView mDataView;
public ProgressBar mProgressBar;
public Context mContext;
private RecyclerView.LayoutManager mLayoutManager;
public Base() { }
@Override
public View onCreateView(LayoutInflater _i, ViewGroup _vg, Bundle savedInstanceBundle){
mView = _i.inflate(R.layout.f_base, null);
mDataView = (RecyclerView) mView.findViewById(R.id.data);
mProgressBar = (ProgressBar)mView.findViewById(R.id.loading);
mLayoutManager = new LinearLayoutManager(mContext);
mDataView.setLayoutManager(mLayoutManager);
mContext = this.getActivity();
return mView;
}
@Override
public void onStart() {
super.onStart();
init();
doWork();
}
public abstract void init();
public abstract void doWork();
}
EDIT
Error Stack Trace:
11-02 12:49:44.171 3708-3708/com.nitrox.digitune E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nitrox.digitune, PID: 3708
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.stopSmoothScroller()' on a null object reference
at android.support.v7.widget.RecyclerView.stopScrollersInternal(RecyclerView.java:1159)
at android.support.v7.widget.RecyclerView.stopScroll(RecyclerView.java:1151)
at android.support.v7.widget.RecyclerView.onDetachedFromWindow(RecyclerView.java:1356)
at android.view.View.dispatchDetachedFromWindow(View.java:13441)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2837)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4163)
at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4136)
at android.view.ViewGroup.removeView(ViewGroup.java:4068)
at android.support.v4.view.ViewPager.removeView(ViewPager.java:1326)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1045)
at android.support.v4.app.FragmentManagerImpl.detachFragment(FragmentManager.java:1280)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:724)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
at android.support.v4.view.ViewPager$3.run(ViewPager.java:249)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:549)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Basically, your LayoutManager is being disposed of before your recycler has finished with it.
From the Android source :
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
if (mItemAnimator != null) {
mItemAnimator.endAnimations();
}
mFirstLayoutComplete = false;
stopScroll();
mIsAttached = false;
if (mLayout != null) {
mLayout.onDetachedFromWindow(this, mRecycler);
}
removeCallbacks(mItemAnimatorRunner);
}
The problem is stopScroll tries to call mLayout.stopSmoothScroller(); without checking if mLayout is null. I threw togeather a very hacky hot fix for an app I've been working on but should NOT be used as a long term solution as it's very much a hack, but I had a tight deadline so I just had to catch the null pointer exception. I cut out my handler because it was application specific.
My hot fix was just to create a custom View extending the RecyclerView :
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
public class HotFixRecyclerView extends RecyclerView
{
public HotFixRecyclerView( Context context )
{
super( context );
}
public HotFixRecyclerView( Context context, AttributeSet attrs )
{
super( context, attrs );
}
public HotFixRecyclerView( Context context, AttributeSet attrs, int defStyle )
{
super( context, attrs, defStyle );
}
@Override
public void stopScroll()
{
try
{
super.stopScroll();
}
catch( NullPointerException exception )
{
/**
* The mLayout has been disposed of before the
* RecyclerView and this stops the application
* from crashing.
*/
}
}
}
Then change all references to the RecyclerView to my own View. If you do use it please remove it once Android have patched this issue as it's a bit of a hack.
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