Question

尝试在C＃应用程序上调试问题，我偶然发现了这个问题，这是导致应用程序出现故障的原因。

基本上我有这段代码：

double scale = 1;
double startScale = 1;
...
scale = (e.Scale - 1) * startScale;
if(scale <= 1)
    scale = 1;
...

即使scale大于1，如果scale最终为1，则执行进入内部会发生什么。

仅在发布版本中发生。

有没有人知道发生了什么？

修改

这几乎是（仅缺少什么不做的，对于Xamarin Forms的自定义控件，取自他们的示例来实现捏合手势（here）。

public class PinchView : ContentView
{
    private double StartScale = 1;
    private double CurrentScale = 1;
    private double XOffset = 0;
    private double YOffset = 0;

    ...

    private void PinchGesture_PinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
    {
        if (e.Status == GestureStatus.Started)
        {
            // Store the current scale factor applied to the wrapped user interface element,
            // and zero the components for the center point of the translate transform.
            StartScale = Content.Scale;
            Content.AnchorX = 0;
            Content.AnchorY = 0;
        }

        if (e.Status == GestureStatus.Running)
        {
            // Calculate the scale factor to be applied.
            CurrentScale += (e.Scale - 1) * StartScale;
            if(CurrentScale <= 1)
            {
                CurrentScale = 1;
            }

            // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
            // so get the X pixel coordinate.
            double renderedX = Content.X + XOffset;
            double deltaX = renderedX / Width;
            double deltaWidth = Width / (Content.Width * StartScale);
            double originX = (e.ScaleOrigin.X - deltaX) * deltaWidth;

            // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
            // so get the Y pixel coordinate.
            double renderedY = Content.Y + YOffset;
            double deltaY = renderedY / Height;
            double deltaHeight = Height / (Content.Height * StartScale);
            double originY = (e.ScaleOrigin.Y - deltaY) * deltaHeight;

            // Calculate the transformed element pixel coordinates.
            double targetX = XOffset - (originX * Content.Width) * (CurrentScale - StartScale);
            double targetY = YOffset - (originY * Content.Height) * (CurrentScale - StartScale);

            // Apply translation based on the change in origin.
            Content.TranslationX = targetX.Clamp(-Content.Width * (CurrentScale - 1), 0);
            Content.TranslationY = targetY.Clamp(-Content.Height * (CurrentScale - 1), 0);

            // Apply scale factor.
            Content.Scale = CurrentScale;
        }

        if (e.Status == GestureStatus.Completed)
        {
            // Store the translation delta's of the wrapped user interface element.
            XOffset = Content.TranslationX;
            YOffset = Content.TranslationY;
        }
    }
}

这些是我的调试会话的步骤（e.Scale已经过优化且不可见，但您可以看到CurrentScale更改的值）：

Answer 1

CurrentScale和StartScale是实例字段，而不是方法字段，因此它们可能受到另一个线程的影响。要检测任何竞争条件，您可以锁定此块并再次调试：

lock (StartScale) {
    // Calculate the scale factor to be applied.
    CurrentScale += (e.Scale - 1) * StartScale;
    if(CurrentScale <= 1)
    {
        CurrentScale = 1;
    }
}

如果这样可行，您应该使用局部变量获得更好的结果，以减少外部干扰（并删除锁定）：

lock (StartScale) {
    // Calculate the scale factor to be applied.
    var localCurrentScale = CurrentScale + (e.Scale - 1) * StartScale;
    if(localCurrentScale <= 1)
    {
        CurrentScale = 1;
    } else CurrentScale = localCurrentScale;
}

您可以使用Redgate Reflector或Telerik JustDecompile（免费）等工具来分析已编译的程序集（它非常易读），并查看编译过程中的优化内容。

N.B。：StartScale是一个错误的锁，但对于这个调试很好。

C＃在发布版本中不起作用

1 个答案: