Is there way in C# to get all parameters which were used with some extension method?
Example:
public static string GlueStrings(this string mystring, string otherString)
{
return mystring + otherstring;
}
In some method in Form1
string string1 = "Glued";
string string2 = string1.GlueStrings("Strings");
In some method in Form2
string string1 = "Foo";
string string2 = string1.GlueStrings("bar");
Is there a way I can create method which would list all parameters used with that method in whole solution, I am interested in parameter otherString from whole solution?
UPDATE:
This with strings is just an example, I need it to work with different types. Like in MVC Controller annonations where you can get all controllers where some annonation is used.
You could keep a static ConcurrentBag in your class and add each parameter to it at runtime.
(concurrent collection for thread safety http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx)
Not the best way to do it when it comes to performance
but you can use MethodBase.GetParameters
Else
how about GlueStrings(this string mystring, params object[] others)
PS: I have not tried it or unit tested it
Update: Example on request by you
Suppose Class Glue have the method GlueStrings then:
ParameterInfo[] parameterInfos = typeof (Glue).GetMethod("GlueStrings").GetParameters();
Related
I'm declaring a string at initialisation as follows
string a = string.Format("Hello {0}", "World.");
Is there a way to subsequently replace the zeroth argument for something else?
If there's no obvious solution, does anybody know of a better way to address the issue. For context, at initialisation I create a number of strings. The text needs to be updated as the program proceeds. I could create a structure comprising an array of strings and an array of objects and then build the final string as required, but this seems ugly, particularly as each instance could have a different number of arguments.
For example,
public class TextThingy
{
List<String> strings;
List<String> arguments;
...
public string ToString()
{
return strings[0] + arguments [0] + strings [1] ...
}
I've tried this, but to no avail.
string b = string.Format(a, "Universe.");
I guess that the argument {0} once populated is then baked into the string that one time.
You could move the format string to a variable like this?
Would that work? If not, please add some more info for us.
string fmt = "Hello {0}";
string a = string.Format(fmt, "World.");
string b = string.Format(fmt, "Universe.");
try string replace, like ...
StringBuilder sb = new StringBuilder("11223344");
string myString =
sb
.Replace("1", string.Empty)
.Replace("2", string.Empty)
.Replace("3", string.Empty)
.ToString();
Similarly to passing a list through a function and adding elements to it, I want to pass a string and add characters to it. However, I do not want to change the reference.
Func(List myList) {
myList.Append("hello");
}
Func(List myList) {
myList = new List();
}
It's like the distinction between the two functions above. In one case you're adding an element to an existing reference to an object, in the other case you are changing the object that is referenced to.
With strings, I have noticed you always(?) change the object that is referenced to. Every solution i've found takes two or more strings, adds them together and returns a new string.
Is there a way to use the same string instance and add one or more characters to this specific instance?
With strings, I have noticed you always(?) change the object that is referenced to.
Because strings are immutable. You can't change a string in .NET. That opens the door to many optimizations (such as string interning), but also has performance issues when you want to build a long string by parts - many allocations and copyings of memory (to concatenate two strings, you have to allocate a third in the length of the two together, then copy them).
So Microsoft created System.Text.StringBuilder. The idea is to create mutable string. The basic methods are Append() (which appends some data, often primitive types) and AppendFormat() (similar to string.Format()). Then you get a normal string by calling to ToString():
void Func(StringBuilder s)
{
s.Append("Hi everyone!");
}
var s = new StringBuilder();
s.Append("a StringBuilder.");
Func(s);
s.ToString(); // "a StringBuilder.Hi everyone!"
Is there a way to use the same string instance and add one or more
characters to this specific instance?
No, but you can do it by using StringBuilder. Pass instance of StringBuilder to a function and append any string to it, it will add string but will refer to same instance of StringBuilder class
public void AppendString(StringBuilder sb) {
sb.Append("hello");
}
This is because string type is mutable, whenever you assign new value to string it creates new string object in memory, but StringBuilder is immutable, it is reference type. StringBuilder modifies without creating new object.
You can try below code,
public static void Main()
{
StringBuilder sb = new StringBuilder("Default Text");
Console.WriteLine($"Before function call: {sb.ToString()}");
AppendString(sb); //Function call
Console.WriteLine($"After function call: {sb.ToString()}");
}
public static void AppendString(StringBuilder sb)
{
sb.Append(" Hello world");
Console.WriteLine($"Inside function: {sb.ToString()}");
}
Output:
Before function call: Default Text
Inside function: Default Text Hello world
After function call: Default Text Hello world
.Net fiddle
I would suggest you to read string vs StringBuilder
You can achieve this by passing string parameter as reference. Please refer to the following code snippet.
static void Main(string[] args)
{
string input = "input";
AddString(ref input);
System.Console.WriteLine(input);
}
private static void AddString(ref string input)
{
input += "_edited";
}
You will need to use ref keyword in both the cases while defining and passing method parameter. Hope it helps.
I'm learning C# and C and this C# code is giving me an error I don't understand. I'm reading about extension methods and this code is giving the error: No overload for method 'WriteTextToConsole' takes 1 arguments. As you can see, it takes exactly 1 arguments? I created the variables c and count only to be able to construct the string object. So I could try the extension in the String class. Is it right understood that the way you create an extension method: is to precede the parameter with the "this" keyword and the parameter is of the type of class to be extended?
The code is here:
Console.WriteLine();
M.WriteTextToConsole("Hello, world. Programming in C# is fun");
char c = 'A';
int count = 14;
String str = new String(c, count);
str.WriteTextToConsole("This is a string");
The method is here:
static class M
{
public static void WriteTextToConsole(this string text)
{
Console.WriteLine(text);
}
}
you need to call it as str.WriteTextToConsole();. In this case str would be passed as a single argument to M.WriteTextToConsole() method
When you call the extension method on the string the "this string text" parameter refers to the string itself,for example if it where "this Bitmap b" it would be an extension method for the bitmap and assuming you had created a bitmap object named bit the call would be bit.WriteTextToConsole().If you want to had other parameters you need to add those to to the method declaration and to make so it is an option for the caller make it with the params keyword like so:
static class M
{
public static void WriteTextToConsole(this string text,params string[] str)
{
if (str.Length > 0)
{
//do something with extra string or strings
//you can make params Object[] but for this
//example i choose string[]
Console.WriteLine(text);
return;
}
Console.WriteLine(text);
}
}
Just remenber the this keyword must be the first parameter,refering to the type you are extending.
In the case of having optional strings i left the code with the duplicate console.WriteLine(text) you can rewrite it if you in both cases want the string displayed in the console(just remove the return and console writeline above it).
As is described at Microsoft Site ,String.Format arranges some String Variables into a single String and is another way how to concate string's in c#.
string.Format("Name = {0} Surname = {1}",name,surname);
My question is how does this work ?
Is this method a Special method ,and can i create a method similar to this one which accepts at every {n} only an Integer .
Or is this method interpreted in a different way by compiler ,if yes than how does the compiler accesses this method .
If it's possible i would like to see ,how does the compiler interpret this Method.
PS : How does it work ,when you can send as much parameters as you want to a method ?
[EDIT]
Does it mean ,that String.Format takes the first Parameter and filter's into with a Regex or Whatever tool (Split etc) to get where {Number} is and places there a String token from second params portion ?
Sending a variable number of parameters to a method is done like this:
public static string MyStringFormat(string formatString, params object [] args)
{
}
You can now pass as many parameters as you like to this:
MyStringFormat("{0}{1}",42,"Hello World")
MyStringFormat("{0}{1}{2}",42,"Hello World",999.9)
Within the method, these arguments are simply an array (of object in this case).
here are the docs on the params keyword.
As for writing you own method to accept numeric input like Format does, this would be one way (using regular expressions):
public static string MyStringFormat(string formatString, params object[] args)
{
var regex = new Regex("{([0-9]*)}");
return regex.Replace(formatString,m =>
{
int index = int.Parse(m.Groups[1].Value);
if(index<args.Length)
return args[index].ToString();
return String.Empty;
});
}
Live example: http://rextester.com/rundotnet?code=OMZC13551
It is a normal function.
It parses the string and calls ToString on the incoming parameters (if needed) in order to construct the new string.
The signature of the overload you have in your example is:
public static string Format(
string format,
params Object[] args
)
There is nothing to stop you from creating your own (though I would probably just delegate to the built in string.Format).
Use params: http://msdn.microsoft.com/en-us/library/w5zay9db.aspx
there is no magic there Cody, look at this method:
public static void UseParams(params int[] list)
{
for (int i = 0 ; i < list.Length; i++)
{
Console.WriteLine(list[i]);
}
Console.WriteLine();
}
you can call it passing as many int you like, it's the params parameter type :)
Edit:
params is very useful it allows us, for example, to pass to our logging wrapper all method's parameters values in a dynamic way without knowing how many of them each method has, the logger will then dump all those values one by one using Reflection to find out the parameter name as well.
The braces in the string are placeholders and a number within that denotes the index of argument it is to be replaced with.
Format is of type (string format, params object[] args) and it is the index in this object[] which is helpful.
(I think it internally uses the StringBuilder.AppendFormat) for substituting those values)
The signature of String.Format looks like this:
public static string Format (string format, params Object[] args)
Note the second parameter, marked with the params keyword. That one provides the functionality to add multiple parameters when calling the function. Inside the function you can access the parameters by index or iterating over args array:
public static string Format (string format, params Object[] args)
{
foreach (Object o in args)
Console.WriteLine(o);
}
Have a look at the C# Reference.
I'm fairly new to C#, and trying to figure out string insertions (i.e. "some {0} string", toInsert), and ran across a problem I wasn't expecting...
In the case where you have two constructors:
public MyClass(String arg1) { ... }
public MyClass(String arg1, String arg2) { ... }
Is it possible for me to use the first constructor with a string insertion?
...
toInsert = "def"
myClass = new MyClass("abc{0}ghi", toInsert)
...
Or will C# interpret this as the second constructor and pass a literal "abc{0}ghi" as the first argument?
Yes, this will be interpreted as just a second parameter.
The behavior you describe is called string formatting and everything that accepts strings in this style uses string.Format() in the background. See the documentation of that method for details.
To get the desired behavior, use this code:
myClass = new MyClass(string.Format("abc{0}ghi", toInsert));
Just do:
public MyClass(string format, params object[] args)
{
this.FormattedValue = string.Format(format, args);
}
Or will C# interpret this as the
second constructor and pass a literal
"abc{0}ghi" as the first argument?
This is the right answer.
I think If you use String.Format("abc{0}ghi", toInsert) then it will take the first constructor