字符串插值是一种语法糖,它编译成字符串格式。这意味着它需要在编译时知道所有细节。在您的情况下,您只能在运行时知道字符串,因此需要使用字符串格式:
<appSettings>
<add key="userNameKey" value="Your User Name is {0}" />
</appSettings>
代码:
var message = string.Format(ConfigurationManager["userNameKey"], userName);
使用插值字符串无法完成此操作。插值字符串中使用的变量应在编译时已知。然而,您可以使用string.Format
来实现您想要的效果。
var result = string.Format(message, userName);
并将消息的值更改为以下内容:
<add key="userNameKey" value="Your User Name is {0}" />
public static class StringExtensions
{
public static string Interpolate(this string self, object interpolationContext)
{
var placeholders = Regex.Matches(self, @"\{(.*?)\}");
foreach (Match placeholder in placeholders)
{
var placeholderValue = placeholder.Value;
var placeholderPropertyName = placeholderValue.Replace("{", "").Replace("}", "");
var property = interpolationContext.GetType().GetProperty(placeholderPropertyName);
var value = property?.GetValue(interpolationContext)?.ToString() ?? "";
self = self.Replace(placeholderValue, value);
}
return self;
}
}
[Fact]
public void Foo()
{
var world = "World";
var someInt = 42;
var unused = "Not used";
//This is a normal string, it can be retrieved from config
var myString = "Hello {world}, this is {someInt}";
//You need to pass all local values that you may be using in your string interpolation. Pass them all as one single anonymous object.
var result = myString.Interpolate(new {world, someInt, unused});
result.Should().Be("Hello World, this is 42");
}
编辑: 对于点表示法的支持: 感谢这个答案。
public static class StringExtensions
{
public static string Interpolate(this string self, object interpolationContext)
{
var placeholders = Regex.Matches(self, @"\{(.*?)\}");
foreach (Match placeholder in placeholders)
{
var placeholderValue = placeholder.Value;
var placeholderPropertyName = placeholderValue.Replace("{", "").Replace("}", "");
var value = GetPropertyValue(interpolationContext, placeholderPropertyName)?.ToString() ?? "";
self = self.Replace(placeholderValue, value);
}
return self;
}
public static object GetPropertyValue(object src, string propName)
{
if (src == null) throw new ArgumentException("Value cannot be null.", nameof(src));
if (propName == null) throw new ArgumentException("Value cannot be null.", nameof(propName));
if (propName.Contains("."))
{
var temp = propName.Split(new char[] {'.'}, 2);
return GetPropertyValue(GetPropertyValue(src, temp[0]), temp[1]);
}
var prop = src.GetType().GetProperty(propName);
return prop != null ? prop.GetValue(src, null) : null;
}
}
正如其他人所提到的,您无法在此情况下使用插值。但是这个怎么样?
string userName = "SnowWhite";
var message = ConfigurationManager.AppSettings["userNameKey"];
message = message.Replace("{userName}", userName);
private static string ConvertInterpolatedStringToFormartString(string interpolatedString)
{
var placeholders = Regex.Matches(interpolatedString, @"\{(.*?)\}").ToArray();
for (int i = 0; i < placeholders.Length; i++)
{
interpolatedString = interpolatedString.Replace(placeholders[i].ToString(), $"{{{i}}}");
}
return interpolatedString;
}