Sending a msg. to a class

  • I'll appreciate someone to help me understand the problem and suggest solution.
    I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it doesn't work from inside the loop.
    Thanks.

    - (IBAction)resetAll: (id)sender {

    //     [toPawn1 showYourself];         //--- This works fine.
    //     .......
    //     [toPawn16 showYourself];

    / but the following generates a warning: 'NSMutableString' may not respond to '-showYourself'

    for (i = 1; i <= 16; ++i) {
      NSMutableString *str = [NSMutableString stringWithFormat: @"toPawn%i", i];
      [ [str className] showYourself];
      [str release];
    }
    }

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  • On 10/25/07, z <zyberk...> wrote:
    >
    > I'll appreciate someone to help me understand the problem and suggest solution.
    > I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it doesn't work from inside the loop.
    > Thanks.
    >
    > - (IBAction)resetAll: (id)sender {
    >
    > //      [toPawn1 showYourself];                //--- This works fine.
    > //      .......
    > //      [toPawn16 showYourself];
    >
    > / but the following generates a warning: 'NSMutableString' may not respond to '-showYourself'

    As it should... unless you added showYourself to NSMutableString via a category.

    > for (i = 1; i <= 16; ++i) {
    > NSMutableString *str = [NSMutableString stringWithFormat: @"toPawn%i", i];
    > [ [str className] showYourself];
    > [str release];
    > }
    > }

    Can you explain what you think above loop does? Better yet explain
    what you are attempting to do in better detail... the above loop
    likely isn't the way to do it (doesn't do what you think it does).

    -Shawn
  • On 25. Oct 2007, at 20:35, z wrote:

    >
    > I'll appreciate someone to help me understand the problem and
    > suggest solution.
    > I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it
    > doesn't work from inside the loop.
    > Thanks.
    >
    > - (IBAction)resetAll: (id)sender {
    >
    > //     [toPawn1 showYourself];         //--- This works fine.
    > //     .......
    > //     [toPawn16 showYourself];
    >
    > / but the following generates a warning: 'NSMutableString' may not
    > respond to '-showYourself'
    >
    > for (i = 1; i <= 16; ++i) {
    > NSMutableString *str = [NSMutableString stringWithFormat: @"toPawn
    > %i", i];
    > [ [str className] showYourself];
    > [str release];
    > }
    > }

    i'm not a pro, but i think i understand the problem. unfortunately, i
    don't know how to solve it.

    ok, here goes:
    className returns the name of the class that your object (in this
    case str) was made from, which is NSMutableString. the second line in
    the for loop sends showYourself to NSMutableString which obviously
    does not know how to respond, so you get that warning.
  • On Oct 25, 2007, at 2:35 PM, z wrote:

    >
    > I'll appreciate someone to help me understand the problem and
    > suggest solution.
    > I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it
    > doesn't work from inside the loop.
    > Thanks.
    >
    > - (IBAction)resetAll: (id)sender {
    >
    > //     [toPawn1 showYourself];         //--- This works fine.
    > //     .......
    > //     [toPawn16 showYourself];
    >
    > / but the following generates a warning: 'NSMutableString' may not
    > respond to '-showYourself'
    >
    > for (i = 1; i <= 16; ++i) {
    > NSMutableString *str = [NSMutableString stringWithFormat: @"toPawn
    > %i", i];
    > [ [str className] showYourself];
    > [str release];
    > }
    > }

    1. You're not sending the showYourself method to the class, but to
    the object that is returned from the -className message, which is an
    NSString instance. That's why you're getting the warning. To get a
    class object from an NSString, you need to use NSClassFromString
    function.
    2. You shouldn't release str, since you didn't alloc, retain or copy
    it. See the docs on memory management.

    NSString* className = [NSString stringWithFormat:@"toPawn%i", i];
    Class theClass = NSClassFromString(className);
    [theClass showYourself];

    Glen
  • On 10/25/07, Glen Simmons <glen.simmons...> wrote:
    > On Oct 25, 2007, at 2:35 PM, z wrote:
    >
    >>
    >> I'll appreciate someone to help me understand the problem and
    >> suggest solution.
    >> I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it
    >> doesn't work from inside the loop.
    >> Thanks.
    >>
    >> - (IBAction)resetAll: (id)sender {
    >>
    >> //    [toPawn1 showYourself];                //--- This works fine.
    >> //    .......
    >> //    [toPawn16 showYourself];
    >>
    >> / but the following generates a warning: 'NSMutableString' may not
    >> respond to '-showYourself'
    >>
    >> for (i = 1; i <= 16; ++i) {
    >> NSMutableString *str = [NSMutableString stringWithFormat: @"toPawn
    >> %i", i];
    >> [ [str className] showYourself];
    >> [str release];
    >> }
    >> }
    >
    >
    > 1. You're not sending the showYourself method to the class, but to
    > the object that is returned from the -className message, which is an
    > NSString instance. That's why you're getting the warning. To get a
    > class object from an NSString, you need to use NSClassFromString
    > function.
    > 2. You shouldn't release str, since you didn't alloc, retain or copy
    > it. See the docs on memory management.
    >
    > NSString* className = [NSString stringWithFormat:@"toPawn%i", i];
    > Class theClass = NSClassFromString(className);
    > [theClass showYourself];

    However it looks like showYourself is an instance method give what
    little information has been posted so far... so I don't think the
    above would do what he wants in the end.

    -Shawn
  • Clearly, "z" has a situation where he declared a bunch of variables

    SomeClass* pawn1;
    SomeClass* pawn2;
    .
    .
    .
    SomeClass* pawn16;

    and wants to iterate over them.

    Unfortunately, "z" also thinks that Obj-C has some way to dynamically
    construct "references by name" to these objects (you can do this in
    JavaScript, for example).

    I'm unaware of any scheme to get this JavaScript like idiom to work
    in Obj-C, certainly none that are as simple as just stuffing all
    those pawns in an array to begin with and iterating over that.

    "z", you should probably spend some time with some of the
    introductory Objective-C docs out there.

    _murat

    On Oct 25, 2007, at 1:52 PM, Shawn Erickson wrote:

    > On 10/25/07, Glen Simmons <glen.simmons...> wrote:
    >> On Oct 25, 2007, at 2:35 PM, z wrote:
    >>
    >>>
    >>> I'll appreciate someone to help me understand the problem and
    >>> suggest solution.
    >>> I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it
    >>> doesn't work from inside the loop.
    >>> Thanks.
    >>>
    >>> - (IBAction)resetAll: (id)sender {
    >>>
    >>> //    [toPawn1 showYourself];                //--- This works fine.
    >>> //    .......
    >>> //    [toPawn16 showYourself];
    >>>
    >>> / but the following generates a warning: 'NSMutableString' may not
    >>> respond to '-showYourself'
    >>>
    >>> for (i = 1; i <= 16; ++i) {
    >>> NSMutableString *str = [NSMutableString
    >>> stringWithFormat: @"toPawn
    >>> %i", i];
    >>> [ [str className] showYourself];
    >>> [str release];
    >>> }
    >>> }
    >>
    >>
    >> 1. You're not sending the showYourself method to the class, but to
    >> the object that is returned from the -className message, which is an
    >> NSString instance. That's why you're getting the warning. To get a
    >> class object from an NSString, you need to use NSClassFromString
    >> function.
    >> 2. You shouldn't release str, since you didn't alloc, retain or copy
    >> it. See the docs on memory management.
    >>
    >> NSString* className = [NSString stringWithFormat:@"toPawn%i", i];
    >> Class theClass = NSClassFromString(className);
    >> [theClass showYourself];
    >
    > However it looks like showYourself is an instance method give what
    > little information has been posted so far... so I don't think the
    > above would do what he wants in the end.
    >
    > -Shawn
  • Ah. Definitely a terminology problem. He referred to sending a
    message to classes, which got me going the wrong direction. Yes, I'd
    definitely recommend that z at least read the intro to ObjC pdf.

    Glen

    On Oct 25, 2007, at 4:27 PM, Murat Konar wrote:

    > Clearly, "z" has a situation where he declared a bunch of variables
    >
    > SomeClass* pawn1;
    > SomeClass* pawn2;
    > .
    > .
    > .
    > SomeClass* pawn16;
    >
    >
    > and wants to iterate over them.
    >
    > Unfortunately, "z" also thinks that Obj-C has some way to
    > dynamically construct "references by name" to these objects (you
    > can do this in JavaScript, for example).
    >
    > I'm unaware of any scheme to get this JavaScript like idiom to work
    > in Obj-C, certainly none that are as simple as just stuffing all
    > those pawns in an array to begin with and iterating over that.
    >
    > "z", you should probably spend some time with some of the
    > introductory Objective-C docs out there.
    >
    > _murat
    >
    >
    > On Oct 25, 2007, at 1:52 PM, Shawn Erickson wrote:
    >
    >> On 10/25/07, Glen Simmons <glen.simmons...> wrote:
    >>> On Oct 25, 2007, at 2:35 PM, z wrote:
    >>>
    >>>>
    >>>> I'll appreciate someone to help me understand the problem and
    >>>> suggest solution.
    >>>> I'm trying to send a msg. to Pawn1 thru Pawn16 classes, but it
    >>>> doesn't work from inside the loop.
    >>>> Thanks.
    >>>>
    >>>> - (IBAction)resetAll: (id)sender {
    >>>>
    >>>> //    [toPawn1 showYourself];                //--- This works
    >>>> fine.
    >>>> //    .......
    >>>> //    [toPawn16 showYourself];
    >>>>
    >>>> / but the following generates a warning: 'NSMutableString' may not
    >>>> respond to '-showYourself'
    >>>>
    >>>> for (i = 1; i <= 16; ++i) {
    >>>> NSMutableString *str = [NSMutableString
    >>>> stringWithFormat: @"toPawn
    >>>> %i", i];
    >>>> [ [str className] showYourself];
    >>>> [str release];
    >>>> }
    >>>> }
    >>>
    >>>
    >>> 1. You're not sending the showYourself method to the class, but to
    >>> the object that is returned from the -className message, which is an
    >>> NSString instance. That's why you're getting the warning. To get a
    >>> class object from an NSString, you need to use NSClassFromString
    >>> function.
    >>> 2. You shouldn't release str, since you didn't alloc, retain or copy
    >>> it. See the docs on memory management.
    >>>
    >>> NSString* className = [NSString stringWithFormat:@"toPawn%i", i];
    >>> Class theClass = NSClassFromString(className);
    >>> [theClass showYourself];
    >>
    >> However it looks like showYourself is an instance method give what
    >> little information has been posted so far... so I don't think the
    >> above would do what he wants in the end.
    >>
    >> -Shawn
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