接受委托函数的扩展方法
本文关键字:方法 扩展 函数 接受委托 | 更新日期: 2023-09-27 18:36:31
我仍在尝试将我的头包裹在委托函数和扩展方法上。我已经为DropDownList
创建了一个扩展方法。我想在我的扩展方法中传递要调用的函数,但我收到错误Argument type 'IOrderedEnumerable<KeyValuePair<string,string>>' is not assignable to parameter type 'System.Func<IOrderedEnumerable<KeyValuePair<string,string>>>'
public static class DropDownListExtensions {
public static void populateDropDownList(this DropDownList source, Func<IOrderedEnumerable<KeyValuePair<string, string>>> delegateAction) {
source.DataValueField = "Key";
source.DataTextField = "Value";
source.DataSource = delegateAction;
source.DataBind();
}
}
被这样称呼...
myDropDownList.populateDropDownList(getDropDownDataSource());
getDropDownDataSource signature...
protected IOrderedEnumerable<KeyValuePair<string,string>> getDropDownDataSource() {
StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument();
string schoolTypeXmlPath = string.Format(STATE_AND_SCHOOL_TYPE_XML_PATH, StateOfInterest, SchoolType);
var nodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>());
return nodes.Distinct().Select(x => new KeyValuePair<string, string>(x.Attributes["area"].Value, x.Attributes["area"].Value)).OrderBy(x => x.Key);
}
调用时,您应该在getDropDownDataSource
后删除()
:
myDropDownList.populateDropDownList(getDropDownDataSource);
编辑:方法组可以隐式转换为具有兼容签名的委托。在这种情况下,getDropDownDataSource
匹配Func<IOrderedEnumerable<KeyValuePair<string,string>>>
的签名,因此编译器会为您应用转换,从而有效地执行
Func<IOrderedEnumerable<KeyValuePair<string,string>>> func = getDropDownDataSource;
myDropDownList.populateDropDownList(func);
是的,在您调用myDropDownList.populateDropDownList(getDropDownDataSource());
getDropDownDataSource()
的行中,它会恢复IOrderedEnumerable<KeyValuePair<string,string>>
。 因此,编译器说您无法将IOrderedEnumerable<KeyValuePair<string,string>>
转换为 Func。 要传递 Func,您可以删除括号,以便像下面这样传递指针myDropDownList.populateDropDownList(getDropDownDataSource);
或者可以直接传递数据源:
myDropDownList.populateDropDownList(() => {
StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument();
string schoolTypeXmlPath = string.Format(STATE_AND_SCHOOL_TYPE_XML_PATH, StateOfInterest, SchoolType);
var nodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>());
return nodes.Distinct().Select(x => new KeyValuePair<string, string>(x.Attributes["area"].Value, x.Attributes["area"].Value)).OrderBy(x => x.Key);
}
但这有点丑。