将强类型属性名称作为参数传递 [英] Passing strongly typed property name as argument

问题描述

我有一个IEnumerable<School>的集合正在传递给扩展 填充DropDownList的方法.我也想通过 DataValueField和DataTextField作为参数，但我希望它们成为 强类型.

I have a collection of IEnumerable<School> that is being passed to an extension method that populates a DropDownList. I would also like to pass the DataValueField and DataTextField as an argument but I wanted them to be strongly typed.

基本上，我不想为DataValueField和DataTextField参数传递string，这很容易出错.

Basically, I don't want to pass a string for the DataValueField and DataTextField arguments, it's error prone.

public static void populateDropDownList<T>(this DropDownList source,
        IEnumerable<T> dataSource,
        Func<T, string> dataValueField,
        Func<T, string> dataTextField) {
    source.DataValueField = dataValueField; //<-- this is wrong
    source.DataTextField = dataTextField; //<-- this is wrong
    source.DataSource = dataSource;
    source.DataBind();
}

这样称呼...

myDropDownList.populateDropDownList(states,
        school => school.stateCode,
        school => school.stateName);

我的问题是，如何将强类型化的DataValueField和DataTextField作为参数传递给populateDropDownList?

My question is, how can I pass the DataValueField and DataTextField strongly typed as an argument to populateDropDownList?

推荐答案

基于乔恩的回答和此帖子，它给我一个主意我将DataValueField和DataTextField作为Expression<Func<TObject, TProperty>>传递给了我的扩展方法.我创建了一个接受该表达式并返回该属性的MemberInfo的方法.然后我只需要打电话给.Name，我就得到了string.

Based off Jon's answer and this post, it gave me an idea. I passed the DataValueField and DataTextField as Expression<Func<TObject, TProperty>> to my extension method. I created a method that accepts that expression and returns the MemberInfo for that property. Then all I have to call is .Name and I've got my string.

哦，我将扩展方法名称更改为populate，这很丑.

Oh, and I changed the extension method name to populate, it was ugly.

public static void populate<TObject, TProperty>(
        this DropDownList source, 
        IEnumerable<TObject> dataSource, 
        Expression<Func<TObject, TProperty>> dataValueField, 
        Expression<Func<TObject, TProperty>> dataTextField) {
    source.DataValueField = getMemberInfo(dataValueField).Name;
    source.DataTextField = getMemberInfo(dataTextField).Name;
    source.DataSource = dataSource;
    source.DataBind();
}

private static MemberInfo getMemberInfo<TObject, TProperty>(Expression<Func<TObject, TProperty>> expression) {
    var member = expression.Body as MemberExpression;
    if(member != null) {
        return member.Member;
    }
    throw new ArgumentException("Member does not exist.");
}

这样称呼...

myDropDownList.populate(states,
    school => school.stateCode,
    school => school.stateName);

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