java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“int android.view.View.getBottom()" [英] java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getBottom()' on a null object reference

问题描述

当我构建和运行它时，它运行良好.但是当我远程重新启动应用程序时出现此错误.

It's working fine when I build and run it. But I'm getting this error when I relaunch the app remotely.

这是我唯一使用 views 的地方.它在 ListAdapter 中.

this is the only place where I used views. It's in ListAdapter.

我在 Google 和 StackOverflow 上环顾四周，找到了一些信息.但是，我还没有让它工作.现在我希望我的代码能得到帮助.

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;
    }

推荐答案

java.lang.NullPointerException:尝试在空对象引用上调用虚方法int android.view.View.getBottom()"

java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getBottom()' on a null object reference

在该视图上调用 getBottom() 时，某些视图变为 null，导致 NullPointerException.

Some view is getting null causing NullPointerException when calling getBottom() on that view.

因此，由于应用程序在本地运行而没有此问题；但不是远程，所以答案将是一种猜测.

So, as the app runs locally without this issue; but not remotely, so the answer will be a kind of a guess.

假设 1: getView 返回空值.

原因: convertView被标记为@Nullable，所以从一开始就可以是null，并且如果条件 if(getItem(position)!= null) 不满足，则可以保持为 null；因此 getView() 可以返回一个 null View.

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.

建议:您需要通过在 if 之外设置 convertView 值来确保 getView 不能返回空值 条件类似于下面的代码片段.

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);
    }

假设 2: convertView 从此表达式为 null convertView = inflater.inflate(resource, parent, false);

Assumption 2: convertView is null from this expression convertView = inflater.inflate(resource, parent, false);

原因:您没有提供传递给 inflate() 的 resource 参数的来源；也许它是一个可以在多个值中变化的变量值；其中之一可以为空；因此也使 convertView 为 null.

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.

建议:

如果 resource 不可更改，您可以通过将其值设置为 R.layout.list_row 来对其进行硬编码；其中 list_row 是列表项的 xml 布局.

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.

如果它是可变的，那么调试它的值以确保它无论如何都不能为空.

And If it's changeable, then debug its value to make sure it can't be null by any means.

这篇关于java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“int android.view.View.getBottom()"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！