英文:
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getBottom()' on a null object reference
问题
这在构建和运行时运行良好。但是在远程重新启动应用程序时出现了这个错误。
这是唯一使用views
的地方。它在ListAdapter
中。
我在Google和StackOverflow上查找了一些信息。然而,我还没有让它正常工作。现在我希望能够得到有关我的代码的帮助。
java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法'int android.view.View.getBottom()'
at android.widget.ListView.fillDown(ListView.java:829)
at android.widget.ListView.fillFromTop(ListView.java:888)
at android.widget.ListView.layoutChildren(ListView.java:1958)
at android.widget.AbsListView.onLayout(AbsListView.java:2991)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
// 更多堆栈跟踪...
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
if(getItem(position)!= null) {
title = getItem(position).getText();
date = getItem(position).getDate();
hour = getItem(position).getHour();
minute = getItem(position).getMinute();
SimpleDateFormat formatter = new SimpleDateFormat("dd MMMM yyyy");
LayoutInflater inflater = LayoutInflater.from(context);
convertView = inflater.inflate(resource, parent, false);
TextView titleView = (TextView) convertView.findViewById(R.id.title);
TextView descpView = (TextView) convertView.findViewById(R.id.description);
TextView dateView = (TextView) convertView.findViewById(R.id.date);
titleView.setText(title);
descpView.setText(hour + ":" + minute);
dateView.setText(formatter.format(date));
}
return convertView;
}
英文:
It's working fine when I build and run it. But I'm getting this error when I relaunch the app remotely.
this is the only place where I used views
. It's in ListAdapter
.
I looked around on both Google and StackOverflow and I have found some information. However, I have not got it to work. Now I hope that I can get help with my code.
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getBottom()' on a null object reference
at android.widget.ListView.fillDown(ListView.java:829)
at android.widget.ListView.fillFromTop(ListView.java:888)
at android.widget.ListView.layoutChildren(ListView.java:1958)
at android.widget.AbsListView.onLayout(AbsListView.java:2991)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:142)
at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:41)
at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1556)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:888)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:1075)
at android.view.View.layout(View.java:22406)
at android.view.ViewGroup.layout(ViewGroup.java:6594)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3394)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2863)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1911)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8526)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
at android.view.Choreographer.doCallbacks(Choreographer.java:761)
at android.view.Choreographer.doFrame(Choreographer.java:696)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7078)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:974)
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
if(getItem(position)!= null) {
title = getItem(position).getText();
date = getItem(position).getDate();
hour = getItem(position).getHour();
minute = getItem(position).getMinute();
SimpleDateFormat formatter = new SimpleDateFormat("dd MMMM yyyy");
LayoutInflater inflater = LayoutInflater.from(context);
convertView = inflater.inflate(resource, parent, false);
TextView titleView = (TextView) convertView.findViewById(R.id.title);
TextView descpView = (TextView) convertView.findViewById(R.id.description);
TextView dateView = (TextView) convertView.findViewById(R.id.date);
titleView.setText(title);
descpView.setText(hour + ":" + minute);
dateView.setText(formatter.format(date));
}
return convertView;
}
答案1
得分: 2
> java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法 'int android.view.View.getBottom()'
在调用 getBottom()
方法时,某个视图获取了空值,导致了 NullPointerException
。
因此,应用在本地运行时没有此问题;但在远程运行时出现了这个问题,因此答案可能是一种猜测。
假设 1: getView
返回了一个空值。
原因: convertView
被标记为 @Nullable
,因此它在一开始可以是 null
,如果条件 if(getItem(position)!= null)
不满足,它仍然可以保持为空;因此 getView()
可以返回一个 null 视图
。
建议: 您需要确保 getView
不能返回空值,可以通过在 if
条件之外设置 convertView
的值,就像下面的代码片段一样。
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(resource, parent, false);
}
假设 2: 从这个表达式 convertView = inflater.inflate(resource, parent, false);
可以得出 convertView
为空。
原因: 您没有提供您传递给 inflate()
的 resource
参数的来源;也许它是一个可以在多个值之间变化的变量值;其中一个值可以为 null;从而使 convertView
也为空。
建议:
如果 resource
是不可更改的,则可以通过将其值硬编码为例如 R.layout.list_row
来设置其值;其中 list_row
是列表项的 xml 布局。
如果它是可更改的,则通过调试其值,确保它不会以任何方式变为 null。
英文:
> java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getBottom()' on a null object reference
Some view is getting null causing NullPointerException
when calling getBottom()
on that view.
So, as the app runs locally without this issue; but not remotely, so the answer will be a kind of a guess.
Assumption 1: getView
returns a null value.
Reason: convertView
is marked as @Nullable
, so it can be null
from the beginning, and can remain null if the condition if(getItem(position)!= null)
is not met; and therefore getView()
can return a null View
.
Recommendation: you need to make sure that getView
can't return null value by setting the convertView
value outside the if
condition like the below snippet.
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
if (converView == null) {
convertView = inflater.inflate(resource, parent, false);
}
Assumption 2: convertView
is null from this expression convertView = inflater.inflate(resource, parent, false);
Reason: You didn't provide from where you got the resource
argument you pass to inflate()
; maybe it's a variable value that can change in multiple values; one of which can be null; and therefore making convertView
null as well.
Recommendation:
If the resource
is not changeable, you can hardcode it by setting its value to say R.layout.list_row
; where list_row
is the xml layout of your list item.
And If it's changeable, then debug its value to make sure it can't be null by any means.
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