Monotouch 在不可为空的对象上因 NullReferenceException 崩溃 [英] Monotouch crashes with NullReferenceException on non nullable object
问题描述
这是崩溃日志(简短):
Here is the crash log ( short ):
2013-04-24 19:56:24 +0000 Memotion 未处理的托管异常:未将对象引用设置为对象的实例 (System.NullReferenceException)
在 Pipedream.UI.UIElement.set_Size(Vector2 值)[0x00000] 中:0
在 Pipedream.UI.StageLayer..ctor (Pipedream.ComponentID id) [0x00000] 中:0
在 Pipedream.UI.Stage.CreateLayer (Pipedream.ComponentID id) [0x00000] 中:0
2013-04-24 19:56:24 +0000 Memotion Unhandled managed exception: Object reference not set to an instance of an object (System.NullReferenceException)
at Pipedream.UI.UIElement.set_Size (Vector2 value) [0x00000] in :0
at Pipedream.UI.StageLayer..ctor (Pipedream.ComponentID id) [0x00000] in :0
at Pipedream.UI.Stage.CreateLayer (Pipedream.ComponentID id) [0x00000] in :0
其实构造函数的代码是这样的:
Actually the code of the constructor looks like this:
internal StageLayer(ComponentID id)
: base(id, ComponentLayer.System)
{
base.Size = ApplicationBase.Instance.ScreenSize;
ApplicationBase.Instance.PropertyChanged += HandlePropertyChanged;
}
该属性如下所示:
public virtual Vector2 Size
{
get
{
return _Size;
}
set
{
Vector2 old = _Size;
if (SetData(SizeDeclaration, value, ref _Size, Invalidate))
{
CompareUpdate(WidthDeclaration, _Size.X, old.X);
CompareUpdate(HeightDeclaration, _Size.Y, old.Y);
}
}
}
好吧,Vector2
是一个结构体,不能为 null
.这段代码也可以在桌面上完美运行.我想不出这段代码应该崩溃的任何原因,但它也不会在 iOS 模拟器上,仅在 iOS 设备上(我目前没有设备,所以我无法直接调试它).
Well the Vector2
is a struct and cannot be null
. Also this code works perfectly on desktop. I can't think of any reason why this code should crash but it also does not on iOS simulator, only on iOS-device ( I currently have no device so i'm not able to debug it directly ).
我在调用这段代码之前启动了一些任务,但是它们使用自己的数据并且不能与当前数据冲突,即使这样也不应该有任何NullReferenceException
.
事实证明,当应该调用 CompareUpdate
方法时会抛出异常.无论如何,我认为非虚拟通用方法不应该有任何问题?
It turns out that the exception is thrown when the CompareUpdate
-method should be called. Anyway i thought that non virtual generic methods should not make any issues?
protected Boolean CompareUpdate<T>(DependencyProperty property, T newValue, T oldValue)
{
if (!Object.Equals(newValue, oldValue))
{
ForceUpdate(property, newValue, oldValue);
return true;
}
return false;
}
编辑 2
在更多的测试用例之后,我发现这可能是一个真正的编译器问题.以下测试失败:
Edit 2
After some more test cases i found out that that this might be a real compiler issue. The following test fails:
Log.Info(_Size.X.ToString()); // _Size is still a struct
除此之外:
System.NullReferenceException:未将对象引用设置为对象的实例
在 System.Single.ToString () [0x00000] 在/Developer/MonoTouch/Source/mono/mcs/class/corlib/System/Single.cs:260
在 Pipedream.UI.UIElement.set_Size (Vector2 value) [0x00031] in C:\WORK\00_PROJECTS\16 Pipedream\00_FRAMEWORK\trunk\Pipedream\UI\UIElement.cs:332
System.NullReferenceException: Object reference not set to an instance of an object
at System.Single.ToString () [0x00000] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System/Single.cs:260
at Pipedream.UI.UIElement.set_Size (Vector2 value) [0x00031] in C:\WORK\00_PROJECTS\16 Pipedream\00_FRAMEWORK\trunk\Pipedream\UI\UIElement.cs:332
如果我将原始代码更改为以下代码也没有错误:
If i change the original code to the following there is also no error:
Vector2 old = _Size;
if (SetData(SizeDeclaration, value, ref _Size, Invalidate))
{
CompareUpdate(WidthDeclaration, 0f, 0f);
CompareUpdate(HeightDeclaration, 0f, 0f);
}
当我删除 SetData
方法时也会发生此错误,因此这不可能是错误原因.我已经检查了这个引用,所以堆栈似乎没问题,但是如果我尝试访问 _Size
s 变量 X
并尝试将它打印到控制台 NullReferenceException再次发生.
This error also occurs when i remove the SetData
-method, so this can't be the error cause. I've checked the this reference so the stack seems to be ok, but if i try to access the _Size
s variable X
and try to print it to the console the NullReferenceException occurs again.
推荐答案
事实证明这存在架构差异错误.Vector2
的 [StructLayout(LayoutKind.Sequential, Pack = 1)]
行导致 Vector2 未对齐,这在某些架构中是非法的.
As it turns out this has an architecture difference bug. The [StructLayout(LayoutKind.Sequential, Pack = 1)]
line of the Vector2
causes the Vector2 to be unaliagned which is illegal in some architectures.
暂时删除该行即可解决问题.
Removing the line for now removed the issue.
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