running a method with object from a string

Question

at one point of my code I have references to methods as strings and I have their targets. For example, suppose I have an object called myObject and I have a method there called "doSomething:" like this:

- (void)doSomething:(id)sender {
   // do something baby
}

at one point of my code I store references to both object and method doing this:

NSString *myMethod = @"doSomething:";
id myTarget = myObject;

later, in another point of the code I want to do this

[myObject doSomething:self];

but how do I reconstruct the method call to that object from an reference id to the object and from a NSString that represents the method and how do I pass self to that method?

thanks

Hint: You want to create a "selector".

Hot Licks
– Hot Licks

2013-02-25 12:45:37 +00:00
Commented Feb 25, 2013 at 12:45 — Hot Licks
– Hot Licks, Commented Feb 25, 2013 at 12:45
use NSSelectorFromString, check the documentation

tkanzakic
– tkanzakic

2013-02-25 12:46:32 +00:00
Commented Feb 25, 2013 at 12:46 — tkanzakic
– tkanzakic, Commented Feb 25, 2013 at 12:46

Till · Accepted Answer · 2013-02-25 12:55:39Z

3

For converting a string towards a selector, use NSSelectorFromString. For the other way around, use NSStringFromSelector.

Convert the selector:

SEL selector = NSSelectorFromString(methodSelectorString);

Invoke method:

[myObject performSelector:selector withObject:self afterDelay:0.0];

From the Foundation reference;

NSSelectorFromString

Returns the selector with a given name.

SEL NSSelectorFromString (
   NSString *aSelectorName
);

Parameters

aSelectorName

A string of any length, with any characters, that represents the name of a selector. Return Value The selector named by aSelectorName. If aSelectorName is nil, or cannot be converted to UTF-8 (this should be only due to insufficient memory), returns (SEL)0.

Discussion To make a selector, NSSelectorFromString passes a UTF-8 encoded character representation of aSelectorName to sel_registerName and returns the value returned by that function. Note, therefore, that if the selector does not exist it is registered and the newly-registered selector is returned.

Recall that a colon (“:”) is part of a method name; setHeight is not the same as setHeight:. For more about methods names, see “Objects, Classes, and Messaging” in The Objective-C Programming Language.

NSStringFromSelector

Returns a string representation of a given selector.

NSString *NSStringFromSelector (
   SEL aSelector
);

edited Feb 25, 2013 at 12:55

answered Feb 25, 2013 at 12:47

Till

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1 Comment

Duck Over a year ago

so? after converting the string to a selector how do I call the method on that object passing self as an object?

Midhun MP · Accepted Answer · 2013-02-25 12:58:26Z

1

As said by @Till, you need to use NSSelectorFromString().

You can use the following code:

SEL selector = NSSelectorFromString(myMethod);
if(selector)
{
   [myObject performSelector:selector withObject:self];
}

answered Feb 25, 2013 at 12:58

Midhun MP

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