在一个代号为iOS的应用程序上研究Java.Lang.NullPointerException [英] Investigate Java.Lang.NullPointerException on a Codename One iOS app

问题描述

今天，我尝试调查此问题： https://github.com/codenameone/CodenameOne / issues / 2975
我在这里写的是问我如何才能准确地找到问题所在。此错误令人沮丧。

Today I tried to investigate this issue: https://github.com/codenameone/CodenameOne/issues/2975 I'm writing here to ask how I can find exactly what goes wrong. This bug is frustrating.

基本上，仅在iOS上，出现此错误，发生在某些随机应用程序使用后：

Basically, on iOS only, I have this error, that happens after some random app usage:

java.lang.NullPointerException
    at com_codename1_ui_Form.pointerReleased:3758
    at net_informaticalibera_cn1_simpleapi_OuterForm.pointerReleased:360
    at com_codename1_ui_Component.pointerReleased:4679
    at com_codename1_ui_Display.handleEvent:2289
    at com_codename1_ui_Display.edtLoopImpl:1214
    at com_codename1_ui_Display.mainEDTLoop:1132
    at com_codename1_ui_RunnableWrapper.run:120
    at com_codename1_impl_CodenameOneThread.run:176
    at java_lang_Thread.runImpl:153

我已覆盖 pointerReleased 方法，以查看抛出前一个异常时 x 和 y 是否可接受的值，似乎是这样：

I've overridden the pointerReleased method to see if x and y are acceptable values when the previous exception is thrown, it seems so:

@Override
    public void pointerReleased(int x, int y) {
        try {
            super.pointerReleased(x, y);
        } catch (Exception ex) {
            Log.p("OuterForm.pointerReleased ERROR, x->" + x + ", y->" + y + ", https://github.com/codenameone/CodenameOne/issues/2975");
            Log.e(ex);
            SendLog.sendLogAsync();
        }
    }

使用该替代，等同于碰撞保护功能，第一次发生此异常后， TextArea 组件将不再可用：点击它们不会打开VKB。

Using that override, that is equivalent to the crash protection feature, after the first time that this exception happens the TextArea components are not more usable: the tap on them doesn't open the VKB.

简而言之，iOS端口 Form.pointerReleased 内有一个 NullPointerException ：如何我可以发现该方法的哪一行引发异常？我希望找到有助于解决错误的信息。

In short, there is a NullPointerException inside the iOS port of Form.pointerReleased: how can I discover which line of that method throws the exception? I hope to find info that can help for the bug resolution.

推荐答案

问题是方法<$ c的代码$ c>类 codename1 / ui / Form.java rel = nofollow noreferrer> Form 都在 try中...最终，隐藏了异常的实际原因。
为了得到实际的原因，我在应用程序的 BaseForm 类中使用了以下覆盖，它扩展了 Form 并且我将其用作所有其他其他形式的超类：

The problem is that the code of the method public void pointerReleased(int x, int y) of the class Form is all inside a try... finally, that hides the actual cause of the exception. To get the actual cause, I used the following override in the BaseForm class of my app, that extends Form and that I use as superclass for all other Forms:

@Override
    public void pointerReleased(int x, int y) {
        try {
            Component cmp = instance.getResponderAt(x, y);
            if (cmp != null) {
                cmp.pointerReleased(x, y);
            }
        } catch (Exception ex) {
            Log.p("BaseForm.pointerReleased ERROR, x->" + x + ", y->" + y + ", https://github.com/codenameone/CodenameOne/issues/2975");
            Log.e(ex);
            SendLog.sendLogAsync();
        }
    }

正如预期的那样，这给了我实际的原因错误，该错误位于 TextArea actionListener的lambda表达式内：更具体而言，问题是在 revalidate 上， code>容器引用在某些情况下可能为 null （奇怪的是，这仅在iOS上发生）。之后，我删除了先前的替代（破坏了某些功能），修复了代码，防止在 null revalidate >对象（条件为 if ）并且错误消失了（我使用该应用程序的长时间使用进行了测试）。

As expected, this gave me the actual cause of the bug, that was inside a lambda expression of a TextArea actionListener: more specifically, the issue was a revalidate on an Container reference that can be null in some circumstances (oddly, this happens only on iOS). After that, I removed the previous override (that broke some functionalities), I fixed my code preventing the revalidate on a null object (with an if condition) and the bug disappeared (I've done a test with a long usage of the app).

这篇关于在一个代号为iOS的应用程序上研究Java.Lang.NullPointerException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！