How to properly create a template string with conditions in C#?-CodePudding

I'm new to C# and have troubles translating my experience into it in certain things. I have two string variables in some class. They can be null or have a word stored in them. I need to create a result string out of them which depends on if they have values or not like in the example: Both variables have values: "string1 (string2)" Only first variable has value: "string1" Only second variable has value: "(string2)" Both are null: ""

So far I came up with this, but I doubt, that this is how it is supposed to be. Seems very rough

var str1 = SomeClass?.Str1   " " ?? string.Empty;
var str2 = "("   SomeClass?.Str2   ")" ?? string.Empty;
var result = $"{str1}{str2}";

Any suggestions? Thanks in advance

CodePudding user response：

You can use StringBuilder class to make the code more readable, an example:

using System.Text;

var sb = new StringBuilder();
if (!string.IsNullOrWhiteSpace(SomeClass?.Str1))
{
    sb.Append($"{SomeClass.Str1} ");
}
if (!string.IsNullOrWhiteSpace(SomeClass?.Str2))
{
    sb.Append($"({SomeClass.Str2})");
}

var result = sb.ToString();

Please note that StringBuilder is more efficient than string concatenation in .NET: https://docs.microsoft.com/en-us/troubleshoot/developer/visualstudio/csharp/language-compilers/string-concatenation

CodePudding user response：

non-null string "null" will result in a non-null string.

"a"   null == "a" // evaluates to true

This means that SomeClass?.Str1 " " and "(" SomeClass?.Str2 ")" will never be null.

Instead, do a null check on the member itself, without the surrounding text.

var result = "";

if (SomeClass?.Str1 is not null)
    result  = SomeClass.Str1;
if (SomeClass?.Str2 is not null)
    result  = " ("   SomeClass.Str1   ")";

You can use StringBuilder as well, but the point of this post is to point out the fallacies with your null checks.

CodePudding user response：

Here is an example of using an extension method that does the job. You can alter as required.

public static StringBuilder AddToString(this StringBuilder sb,string s)
{
if(!string.IsNullOrWhiteSpace(s))
sb.Append($"{s}");
return sb;
}

Usage

var sb = new StringBuilder();
sb.AddToString("a").AddToString("").AddToString("c");
Console.Write(sb.ToString());

//Result: ac //as there is a blank string.

CodePudding user response：

As suggested by Alik, I would recommend looking into StringBuilder.

You can do a lot of cool and advanced stuff like .AppendFormat("Foo {0}{1}{3}", 'B', 'a', 'r').

For more info/features have a look at: https://docs.microsoft.com/en-us/dotnet/api/system.text.stringbuilder