DropDownListFor(...)默认情况下选择布尔值false [英] DropDownListFor(...) selecting boolean false by default

问题描述

我在应用程序中有典型的YesNo下拉列表.为此，我为将来的扩展开发了模型(而不是ViewModel Utility)类.

I have typical YesNo kind of dropdown in the application. For that, I have developed model (rather ViewModel Utility) class for future extension prupose.

public string Text { get; set; } // represents text part
        public bool Value { get; set; } // represent value
        public List<DropDown> DropDowns { get; set; } //list for binding
        public void BuildYesNoDropDown()
        {
            DropDowns = new List<DropDown>();
            DropDowns.Add(new DropDown { Text = "Yes", Value = true });
            DropDowns.Add(new DropDown { Text = "No", Value = false });
        }

然后，将其绑定在如下视图中:

Then, I bind it in view like following:

@Html.DropDownListFor(x => x.SelectedValue, new SelectList(Model.DropDowns, "Value", "Text",1),"Select") //last para - OptionLabel

在视图上，所有三个参数都将显示，即选择"，是"和否".但是，默认情况下已选择否".如果我将值"属性设置为整数，则可以正常工作，并且默认情况下会选择选择"，但是如代码中所述，如果我倾向于使用布尔类型，则会选择否".

On the view, all three parameters are getting display i.e. "Select", "Yes" and "No". But, by default "No" has been selected. If I make "Value" property as integer then it works fine and by default "Select" gets selected, but as mentioned in the code, if I tend to go with bool type then "No" gets selected.

当DataValueField为bool时如何获得正常行为?

How to get normal behavior when DataValueField is bool?

推荐答案

型号:

public bool? Value { get; set; }

查看:

@Html.EditorFor(model => model.Value)

这会自动创建一个下拉列表，其中包含3个与可空布尔的3个状态相匹配的状态:null，true，false.如果您需要回答值"，则可以使用如下数据注释:

This makes a drop down list automatically with 3 states that match the 3 states of a nullable bool: null, true, false. If you require that Value be answered you can use data annotations like so:

型号:

[Required]
public bool? Value { get; set; }

要点是，您的模型需要是一个真实的模型-它需要对未设置到设置的输入值进行建模.如果需要输入int，则可能需要使用可为null的int(即int?)并需要该值.这样，初始值将为null而不是0.它与其他数据类型类似，除了string已经可以为空.

The takeaway is your model needs to be a real model -- it needs to model the input values from unset to set. If you need to input a int, you'll likely want to use a nullable int (so int?) and require the value. That way the initial value is null instead of 0. It is similar with other data types except string which is already nullable.

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