为什么SelectTemplate方法在调试模式下运行2次？ [英] Why is the SelectTemplate Method run 2 times in debug mode?

问题描述

调试此类SelectTemplate方法运行2次，但为什么？

debuging this class the SelectTemplate Method is run 2 times, but why?

第一次项目始终为空。

public class PersonDataTemplateSelector : DataTemplateSelector
{
    public override DataTemplate SelectTemplate(object item,DependencyObject container)
    {
        if (item is Person)
        {
            Person person = item as Person;

            Window window = Application.Current.MainWindow;

            if (System.ComponentModel.DesignerProperties.GetIsInDesignMode( window))
                return null;

            if (person.Gender == "male")               
                return window.FindResource("boysViewTemplate") as DataTemplate;
            else                
                return window.FindResource("girlsViewTemplate") as DataTemplate;

        }
        return null;
    }
}

推荐答案

您的选择器将提供空或加载，第一次调用是什么让您的选择器有机会提供该模板，而元素正在加载。

If your selector were to provide a look for "Empty" or "Loading", the first call is what gives your selector the opportunity to provide that template while the elements are loading.

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