Let's first confess a lie: here and there in this documentation, you have been reading that Mustache tags renders objects in a way or another: variable tags output values HTML-escaped, sections tags loop over arrays, etc.
This is an illusion. Data objects actually have full control on their rendering:
NSArray does render the {{# items }}...{{/}} tag for each of its items.
NSNumber does render as a string for {{ number }}, and decides if {{# condition }}...{{/}} should render or not.
etc.
Your objects that conform to the GRMustacheRendering protocol also take full control of their rendering.
This protocol declares the method that all rendering objects must implement. NSArray does implement it, so does NSNumber, and NSString. Your objects can, as well:
@protocol GRMustacheRendering <NSObject>
- (NSString *)renderForMustacheTag:(GRMustacheTag *)tag
context:(GRMustacheContext *)context
HTMLSafe:(BOOL *)HTMLSafe
error:(NSError **)error;
@end-
The tag represents the tag you must render for. It may be a variable tag
{{ name }}, a section tag{{# name }}...{{/}}, etc. -
The context represents the context stack, and all information that tags need to render.
-
HTMLSafe is a pointer to a BOOL: upon return, it must be set to YES or NO, depending on the safety of the string you render. If you forget to set it, it is of course assumed to be NO. Returning NO would have GRMustache HTML-escape the returned string before inserting it in the final rendering of HTML templates (see the HTML vs. Text Templates Guide for more information).
-
error is... the eventual error. You can return nil without setting any error: in this case, everything happens as if you returned the empty string.
You may declare and implement your own conforming classes. The +[GRMustache renderingObjectWithBlock:] method comes in handy for creating a rendering object without declaring any class:
id renderingObject = [GRMustache renderingObjectWithBlock:^NSString *(GRMustacheTag *tag, GRMustacheContext *context, BOOL *HTMLSafe, NSError **error)
{
return @"I'm rendered!";
}];Let's write a rendering object which wraps a section in a <strong> HTML tag:
Document.mustache:
{{#strong}}
{{name}} is awesome.
{{/strong}}
Render.m:
id strong = [GRMustache renderingObjectWithBlock:^NSString *(GRMustacheTag *tag, GRMustacheContext *context, BOOL *HTMLSafe, NSError **error)
{
// First perform a raw rendering of the tag, using its
// `renderContentWithContext:HTMLSafe:error` method.
//
// We'll get `Arthur is awesome.`
NSString *rawRendering = [tag renderContentWithContext:context HTMLSafe:HTMLSafe error:error];
// Return the raw rendering, wrapped in a <strong> HTML tag:
return [NSString stringWithFormat:@"<strong>%@</strong>", rawRendering];
}];
id data = @{
@"name": @"Arthur",
@"strong": strong,
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
<strong>Arthur is awesome.</strong>
Variable tags such as {{ name }} don't have much inner content. But section tags do: {{# name }} inner content {{/ name }}.
The renderContentWithContext:HTMLSafe:error: method returns the rendering of the inner content, processing all the inner tags with the provided context.
It also sets the HTMLSafe boolean for you, so that you do not have to worry about it. GRMustache templates render HTML by default, so HTMLSafe will generally be YES. There are also text templates (see the HTML vs. Text Templates Guide): in this case, HTMLSafe would be NO. Depending on how reusable you want your rendering object to be, you may have to deal with it.
Your rendering objects can thus delegate their rendering to the tag they are given. They can render the tag once or many times:
Document.mustache:
{{#twice}}
Mustache is awesome!
{{/twice}}
Render.m:
id data = @{
@"twice": [GRMustache renderingObjectWithBlock:^NSString *(GRMustacheTag *tag, GRMustacheContext *context, BOOL *HTMLSafe, NSError *__autoreleasing *error) {
NSMutableString *buffer = [NSMutableString string];
[buffer appendString:[tag renderContentWithContext:context HTMLSafe:HTMLSafe error:error]];
[buffer appendString:[tag renderContentWithContext:context HTMLSafe:HTMLSafe error:error]];
return buffer;
}]
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
Mustache is awesome!
Mustache is awesome!
Let's write a rendering object that wraps a section in a HTML link. The URL of the link will be fetched with the url key:
Document.mustache:
{{#link}}{{firstName}} {{lastName}}{{/link}}
Render.m:
id link = [GRMustache renderingObjectWithBlock:^NSString *(GRMustacheTag *tag, GRMustacheContext *context, BOOL *HTMLSafe, NSError **error)
{
// Build an alternate template string by wrapping the inner content of
// the section in a `<a>` HTML tag:
//
// We'll get `<a href="{{url}}">{{firstName}} {{lastName}}</a>`
NSString *innerTemplateString = tag.innerTemplateString;
NSString *format = @"<a href=\"{{url}}\">%@</a>";
NSString *templateString = [NSString stringWithFormat:format, innerTemplateString];
// Build a new template, and return its rendering:
GRMustacheTemplate *template = [GRMustacheTemplate templateFromString:templateString error:NULL];
return [template renderContentWithContext:context HTMLSafe:HTMLSafe error:error];
}];
id data = @{
@"firstName": @"Orson",
@"lastName": @"Welles",
@"url": @"/people/123",
@"link": link,
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
<a href="/people/123">Orson Welles</a>
Again, variable tags such as {{ name }} don't have much inner content, but section tags do: {{# name }} inner content {{/ name }}.
The innerTemplateString property returns the raw content of the section, with Mustache tags left untouched.
You can derive new template strings from this raw content, even by appending new tags to it (the {{url}} tag, above).
From those template strings, you create template objects, just as you usually do. Their renderContentWithContext:HTMLSafe:error: method render in the given context.
It also sets the HTMLSafe boolean for you, so that you do not have to worry about it. GRMustache templates render HTML by default, so HTMLSafe will generally be YES. There are also text templates (see the HTML vs. Text Templates Guide): in this case, HTMLSafe would be NO. Depending on how reusable you want your rendering object to be, you may have to deal with it.
When a {{> name }} Mustache tag occurs in a template, GRMustache renders in place the content of another template, the partial, identified by its name.
Such partials are hard-coded.
You can still choose the rendered partial at runtime, with simple variable tags:
Document.mustache:
{{#items}}
- {{link}}
{{/items}}
Movie.mustache:
<a href="{{url}}">{{title}}</a>
Person.mustache:
<a href="{{url}}">{{firstName}} {{lastName}}</a>
Render.m:
id data = @{
@"items": @[
@{
@"title": @"Citizen Kane",
@"url":@"/movies/321",
@"link": [GRMustacheTemplate templateFromResource:@"Movie" bundle:nil error:nil],
},
@{
@"firstName": @"Orson",
@"lastName": @"Welles",
@"url":@"/people/123",
@"link": [GRMustacheTemplate templateFromResource:@"Person" bundle:nil error:nil],
},
],
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
- <a href="/movies/123">Citizen Kane</a>
- <a href="">Orson Welles</a>
Let's say a handy technique: we haven't use the GRMustacheRendering protocol here, because GRMustacheTemplate does it for us.
Document.mustache:
{{# items }}
- {{ render(partial) }}
{{/ items }}
Movie.mustache:
<a href="{{url}}">{{title}}</a>
Person.mustache:
<a href="{{url}}">{{firstName}} {{lastName}}</a>
Render.m:
id data = @{
@"items": @[
@{
@"title": @"Citizen Kane",
@"url":@"/movies/321",
@"partial": @"Movie",
},
@{
@"firstName": @"Orson",
@"lastName": @"Welles",
@"url":@"/people/123",
@"partial": @"Person",
},
],
@"render": [GRMustacheFilter filterWithBlock:^id(id value) {
return [GRMustacheTemplate templateFromResource:value bundle:nil error:NULL];
}],
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
- <a href="/movies/123">Citizen Kane</a>
- <a href="">Orson Welles</a>
Well, filters that return rendering objects are awesome.
The above example is somewhat contrived, but you'll see a much more useful example in the Indexes Sample Code.
Let's implement something similar to Ruby on Rails's <%= render @movie %>:
Document.mustache:
{{movie}}
Movie.mustache:
{{title}} by {{director}}
Person.mustache:
{{firstName}} {{lastName}}
Render.m:
Person *director = [Person personWithFirstName:@"Orson" lastName:@"Welles"];
Movie *movie = [Movie movieWithTitle:@"Citizen Kane" director:director];
id data = @{ @"movie": movie };
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
<Movie: 0x1011052a0>
Oops. GRMustache is written in Objective-C, not Ruby: there is no built-in automagic rendering of an object with a partial, through some conversion from a class name to a partial name.
We have to explicitely have our Movie and Person classes render with their dedicated Movie.mustache and Person.mustache partials:
// Declare categories on our classes so that they conform to the
// GRMustacheRendering protocol:
@interface Movie(GRMustache)<GRMustacheRendering>
@end
@interface Person(GRMustache)<GRMustacheRendering>
@end
// Now implement the protocol:
@implementation Movie(GRMustache)
- (NSString *)renderForMustacheTag:(GRMustacheTag *)tag context:(GRMustacheContext *)context HTMLSafe:(BOOL *)HTMLSafe error:(NSError **)error
{
// Extract the "Movie.mustache" partial from the original templateRepository:
GRMustacheTemplate *partial = [tag.templateRepository templateNamed:@"Movie" error:NULL];
// Add self to the top of the context stack, so that the partial
// can access our keys:
context = [context contextByAddingObject:self];
// Return the rendering of the partial
return [partial renderContentWithContext:context HTMLSafe:HTMLSafe error:error];
}
@end
@implementation Person(GRMustache)
- (NSString *)renderForMustacheTag:(GRMustacheTag *)tag context:(GRMustacheContext *)context HTMLSafe:(BOOL *)HTMLSafe error:(NSError **)error
{
// Extract the "Person.mustache" partial from the original templateRepository:
GRMustacheTemplate *partial = [tag.templateRepository templateNamed:@"Person" error:NULL];
// Add self to the top of the context stack, so that the partial
// can access our keys:
context = [context contextByAddingObject:self];
// Return the rendering of the partial
return [partial renderContentWithContext:context HTMLSafe:HTMLSafe error:error];
}
@endFinal rendering:
Citizen Kane by Orson Welles
Many useful things.
-
GRMustacheRenderingis a protocol.Surely
+[GRMustache renderingObjectWithBlock:]is convenient since it lets us create rendering objects from scratch. Yet the protocol is available for you to use on your custom classes. -
The tag provides a template repository.
This object lets you load partials from the same set of templates as the "main" rendering template, the one that did provide the rendered tag (check the Template Repositories Guide if you haven't yet).
This does not make much difference when all templates are loaded from your main bundle. But some of you manage their sets of templates differently.
Caveat: Make sure you own (retain) template repositories. Don't use templates returned by methods like
[GRMustacheTemplate templateFrom...]: they return autoreleased templates with an implicit autoreleased repository that will eventually be deallocated when your rendering object tries to access it. -
Rendering objects manage the context stack.
When GRMustache renders
{{ name }}, it looks for thenamekey in the context stack: for the title and names of our movies and people to render, movies and people must enter the context stack. This is the reason for the derivation of new contexts, using thecontextByAddingObject:method, before partials are rendered.There is also a
contextByAddingTagDelegate:method, that is illustrated in the Delegates Guide.
Using the same Movie and Person class introduced above, we can easily render a list of movies, just as Ruby on Rails's <%= render @movies %>:
Document.mustache:
{{movies}} {{! one movie is not enough }}
Movie.mustache:
{{title}} by {{director}}
Person.mustache:
{{firstName}} {{lastName}}
Render.m:
id data = @{
@"movies": @[
[Movie movieWithTitle:@"Citizen Kane"
director:[Person personWithFirstName:@"Orson" lastName:@"Welles"]],
[Movie movieWithTitle:@"Some Like It Hot"
director:[Person personWithFirstName:@"Billy" lastName:@"Wilder"]],
]
};
NSString *rendering = [GRMustacheTemplate renderObject:data
fromResource:@"Document"
bundle:nil
error:NULL];Final rendering:
Citizen Kane by Orson Welles
Some Like It Hot by Billy Wilder
A new perspective on the fact that arrays render the concatenation of their items.
The Mustache specification does not have the concept of "rendering objects".
However, many of the techniques seen above can be compared to "Mustache lambdas".
You can write specification-compliant "Mustache lambdas" with rendering objects. However those are more versatile.
As a consequence, if your goal is to design templates that remain compatible with other Mustache implementations, use GRMustacheRendering with great care.
The Collection Indexes Sample Code uses the GRMustacheRendering protocol for rendering indexes of an array items.
The localize helper of the standard library uses the protocol to localize full template sections, as in {{# localize }}Hello {{name}}{{/ localize }}.
Last but not least, NSFormatter instances are rendering objets as well, so that {{#decimal}}{{x}}+{{y}}={{sum}}{{/decimal}} would render nice decimal numbers. Check the NSFormatter Guide.