当文本框中未填充任何内容时，将 mvvm WPF 中的属性设置为 null [英] Set null to property in mvvm WPF when nothing is filled in textbox

问题描述

我实现了一个文本框，它绑定到一个视图模型.例如，我将文本框默认填写为100"，但如果我将其更改为 10，则该属性始终设置正确.但是当我删除所有数字时，我希望该属性设置为空.但它只是在什么都没有填写时不设置值.他只是保留最后一个值..

I implemented a textbox, and this binds to a viewmodel. I fill in the textbox default by '100' for example, but if i change this to 10, the property always sets correctly. But when i delete all the numbers, i want that the property is set to null. But it just don't set the value when nothing is filled in. He just keeps the last value..

这是我的代码，viewmodel + xaml:

this is my code , viewmodel + xaml:

public double MaxTime
{
    get
    {
        return maxTime;
    }
    set
    {
        maxTime = value;
        OnPropertyChanged("MaxTime");
        if (SelectedQuestionDropList != null)
        {
            foreach (QuestionCluster cluster in this.Examination.QuestionClusters)
            {
                if (cluster == SelectedQuestionDropList)
                {
                    cluster.MaxTime = value;
                }
            }
        }
    }
}


<TextBox Height="23" 
         Visibility="{Binding Path=VisibleClusterDetails, Converter={StaticResource boolToVis},UpdateSourceTrigger=PropertyChanged}"  
         Text="{Binding Path=MaxTime,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"
         HorizontalAlignment="Right" Margin="0,511,601,0" Name="textBox2" 
         VerticalAlignment="Top" Width="120" /> 

推荐答案

您的属性是双精度值，因此它不支持 null 或空值.

Your property is a double so it won't support null or empty values.

这里不使用双精度值，而是将属性作为字符串公开，并在属性 getter 和 setter 中在字符串和双精度值之间转换.在 setter 中，我可以根据需要处理空值或空值，并且可以轻松处理所需的任何特殊格式.

Instead of using a double here I would expose the property as a string and convert between string and double in my property getter and setter. In the setter I could handle null or empty values as I wanted, and I could easily handle any special formatting that was needed.

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