清除文本框时属性的值不会改变 [英] Value of the property does not change when the textbox is cleared

问题描述

我有一个名为 HaemogramViewModel 的 ViewModel

I have a ViewModel Called HaemogramViewModel

代码如下:

public class HaemogramViewModel : INotifyPropertyChanged
    {
        public HaemogramViewModel()
        {

        }

        public Haemogram CurrentHaemogramReport
        {
            get
            {
                return MainWindowViewModel.cHaemogram;
            }
            set
            {
                MainWindowViewModel.cHaemogram = value;
                OnPropertyChanged("CurrentHaemogramReport");
            }
        }


        protected virtual void OnPropertyChanged(string PropertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(PropertyName));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

    }
}

在我的 MainWindowViewModel 类中:

In my MainWindowViewModel Calss:

class MainWindowViewModel : INotifyPropertyChanged
{
    public MainWindowViewModel()
    {
            cHaemogram = new Haemogram();
    }

    public static Haemogram cHaemogram { get; set; }

    private void SaveChanges(object obj)
    {
        using (Lab_Lite_Entities db = new Lab_Lite_Entities())
        {

            //db.Patients.Add(CurrentPatient);

            if (cHaemogram != null)
            {
                if (cHaemogram.Haemoglobin != null)
                {
                    db.Haemograms.Add(cHaemogram);
                }
            }
        }
    }   
}

我的文本框绑定到 CurrentHaemogram 属性的 Hemoglobin 字段.

My textbox is bound to the field Haemoglobin of CurrentHaemogram Property.

当我在文本框中输入一些值然后单击保存按钮时，一切正常.

When I enter some value in the textbox and then click save button then everything works fine.

现在的问题是:

当我在文本框中输入某个值时，我按 Tab 键，然后再次单击文本框，然后清除文本框中的值.现在，如果我点击保存按钮，那么我不会得到文本框的值 = null，而是得到文本框的值 = 我之前输入的值.

When I enter some value in the textbox then I press tab and then again click on textbox and then clear the value in the textbox. Now if I click on save button then I don't get the textbox's value = null, instead I get the textbox's value = the value that I entered previously.

推荐答案

试试看吧

<TextBox Text="{Binding B, UpdateSourceTrigger=PropertyChanged, TargetNullValue=''}"/>

并且在您的视图中模型属性应如下声明

and in you view model property should be declared as below

 private double? b;
    public double? B
    {
        get
        {
            return b;
        }
        set
        {
            b = value;
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs("B"));
            }
        }
    }

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