objective c macros

Question

I want to use these lines of code from this source

#define TEXTVIEW_SET_HTML_TEXT(__textView__, __text__)\
do\
{\
    if ([__textView__ respondsToSelector: NSSelectorFromString(@"setContentToHTMLString:")])\
        [__textView__ performSelector: NSSelectorFromString(@"setContentToHTMLString:") withObject: __text__];\
    else\
        __textView__.text = __text__;\
}\
while (0)

#define TEXTVIEW_GET_HTML_TEXT(__textView__, __text__)\
do\
{\
    if ([__textView__ respondsToSelector: NSSelectorFromString(@"contentAsHTMLString")])\
        __text__ = [__textView__ performSelector: NSSelectorFromString(@"contentAsHTMLString") withObject: nil];\
    else\
        __text__ = __textView__.text;\
}\
while (0)

What should I do? I am new to macros. Should i define a uitextview variable with name __textView__?? Is it possible to help me with some basic steps in order to use this code?

Answer 1

You just have to put your macros outside your @implementation, something like this:

#import "..."

// Put the macros here

// This block may or may not be present in your code...
@interface YourClass ()

@end
// ... up to here.

@implementation YourClass

@end

You don't have to declare the variables, as these are already declared in the macro. You can think of this:

#define TEXTVIEW_SET_HTML_TEXT(__textView__, __text__)\
do\
{\
    if ([__textView__ respondsToSelector: NSSelectorFromString(@"setContentToHTMLString:")])\
        [__textView__ performSelector: NSSelectorFromString(@"setContentToHTMLString:") withObject: __text__];\
    else\
        __textView__.text = __text__;\
}\
while (0)

as this C-style function:

void TEXTVIEW_SET_HTML_TEXT(UITextView *__textView__, NSString *__text__)
{
    do
    {
        if ([__textView__ respondsToSelector: NSSelectorFromString(@"setContentToHTMLString:")])
            [__textView__ performSelector: NSSelectorFromString(@"setContentToHTMLString:") withObject: __text__];
        else
            __textView__.text = __text__;
    }
    while (0);
}

The difference is that if you have declared it as a C-style function, it would be included in your app when it is compiled/linked. However, since it was #defined, it means the compiler would change it first to the do-while before compiling.

You would call it like this:

- (void)yourMethodThatWillChangeTheText
{
    // ...
    TEXTVIEW_SET_HTML_TEXT(self.myTextView, @"Hello");
    // ...
}

As an additional info, #define is usually used to define constants, something like:

#define PI_VALUE 3.141592

which would have to be called something like:

double circumference = 2 * PI_VALUE * radius;

But as seen in the macro, it can also look/be used as a function. Thus, you have to consider how the macro/#define looks like to be sure that you call it properly.