我有下一个字符串：
public const string BaseAddress = "http://test.i-swarm.com/i-swarm/api/v1/";
public const string LoginURL = "{0}sessions";
我想创建一个 LoginURL 的 URL，其中 {0} 是 BaseAddress。逻辑方法不起作用：
string str = string.Format(BaseAddress, LoginURL);
它只打印 BaseAddress。如果我这样做，它将起作用：
string str = string.Format(LoginURL, BaseAddress); //Is this the correct way?
It's not logical way, you are defining parameter in LoginUrl not in BaseAddress, so it's working correctly
If you want it work logicaly do it that way:
public const string BaseAddress = "http://test.i-swarm.com/i-swarm/api/v1/{0}";
public const string LoginURL = "sessions";
string.Format is replacing {0} with first parameter, so it will now work like you want it to work.
string str = string.Format(LoginURL, BaseAddress); //Is this the correct way?
Yes, that is the correct way. Although it doesn't follow the usual pattern people use. Please read the documentation for the function located here: http://msdn.microsoft.com/en-us/library/system.string.format.aspx
The first argument is the Format, the second are the arguments/replacement values. Assuming you want to maintain a constant format, that is usually a hardcoded in the argument as such:
string str = string.Format("{0}sessions", BaseAddress);
Being as it seems the base address is normally more consistent (but may still be variable) an approach such as the following may be better:
public const string BaseAddress = "http://test.i-swarm.com/i-swarm/api/v1/";
public const string LoginURL = "sessions";
string str = string.Format("{0}{1}", BaseAddress, LoginURL);
If your end-goal is just URL combination rather than an exercise using string.Format, the following may still be a better approach:
Uri baseUri = new Uri("http://test.i-swarm.com/i-swarm/api/v1/");
Uri myUri = new Uri(baseUri, "sessions");
That way you don't have to worry about whether or not a separator was used in the base address/relative address/etc.
没有合乎逻辑的方法，只有一种方法可以遵守String.Format工作原理。String.Format定义为使第一个参数包含要插入参数的字符串，然后是参数列表。
如果你像你一样定义字符串，唯一正确的方法是
string str = string.Format(LoginURL, BaseAddress);
BaseAddress但是，如果是格式字符串，它会更直观：
public const string BaseAddress = "http://test.i-swarm.com/i-swarm/api/v1/{0}";
public const string LoginURL = "sessions";
所以你可以写
string str = String.Format(BaseAddress, LoginURL);
Yes the correct way is:
string str = String.Format(LoginURL, BaseAddress);
The format string should always be the first parameter.
Though I feel that:
string str = String.Format("{0}sessions", BaseAddress);
Is more readable.
您可以使用 C# 的插值字符串。
string BaseAddress = "http://test.i-swarm.com/i-swarm/api/v1/";
string LoginURL = $"{BaseAddress}sessions";
你可以有多个参数。这是一种更安全的格式化字符串的方法，因为在使用 string.Format 时，您需要确保参数的顺序正确。使用这种新方式，您不必这样做。
string foo = "foo";
int bar = 4;
string result = $"{bar} hello {foo}";
参考：