Why when I use method respondsToSelector: or instancesRespondToSelector: at line 43 I cannot bypass STAssertTrue?
//My test case code
- (void)testApiClass {
//Check object
NSString* classKey = #"Api";
id obj = NSClassFromString(classKey);
STAssertNotNil(obj, [NSString stringWithFormat:#"Model '%#' not found.", classKey]);
//Check properties
NSArray* properties =
#[
#"performSyncRequestWithUri::",
#"performAsyncRequestWithUri:::",
];
for (NSString* property in properties) {
SEL propertySel = NSSelectorFromString(property);
BOOL isRespondsToSel = [obj respondsToSelector:propertySel];
STAssertTrue(isRespondsToSel, [NSString stringWithFormat:#"Property '%#' not found on object of class name '%#'", property, [obj class]]);
}
}
#interface Api : NSObject
- (NSDictionary*)performSyncRequestWithUri:(NSString *)requestUri params:(NSDictionary *)params;
- (void)performAsyncRequestWithUri:(NSString *)requestUri params:(NSDictionary *)params completionHandler:(void (^)(NSDictionary *, NSError *))completionBlock;
#end
The string constants in your properties array don't match the selectors in your Api interface.
Also, neither of those selectors refers to a property. A property has two selectors: a getter, like stringValue, which has no colons, and a setter, like setStringValue:, which has one colon and (usually) starts with set.
Instead of embedding your selectors in strings, make an array of selectors:
SEL selectors[] = {
#selector(performSyncRequestWithUri:params:),
#selector(performAsyncRequestWithUri:params:completionHandler:),
NULL
};
for (size_t i = 0; selectors[i]; ++i) {
SEL selector = selectors[i];
BOOL respondsToSelector = [obj respondsToSelector:selector];
STAssertTrue(respondsToSelector, [NSString stringWithFormat:
#"Object %# doesn't respond to selector %s",
obj, sel_getName(selector)]);
}
The advantages here are that Xcode will autocomplete the selectors for you, and you can command-click the selectors to jump to their definitions.
The methods are called performAsyncRequestWithUri:params:completionHandler: and performSyncRequestWithUri:params:
Related
I would like to pass a variable argument list from one method (functionOne) to another (functionTwo). Everything works fine, except that I have not been able to figure out how to setup the va_list in functionTwo in a way where I can access the first parameter in the va_list. Using va_arg advances to the second parameter in the va_list. Thx.
- (void)functionOne:(NSString *)configFiles, ... {
va_list args;
va_start(args, configFiles);
[self functionTwo:args];
va_end(args);
}
- (void)functionTwo:(va_list)files {
NSString *file;
while ((file = va_arg(configFiles, NSString *))) {
...
}
}
The first variadic argument is not the argument passed to va_start – it's the one immediately following it. If you want functionTwo: to have access to the configFiles string, you'll need to pass it in explicitly.
See Technical Q&A QA1405: Variable arguments in Objective-C methods.
Methods that take variable arguments are known as variadic methods.
Keep in mind that the implementation of an Objective-C method is just
a block of code, like a C function. The variadic argument macros
described in the stdarg(3) manual page work the same way in a method
as they do in an ordinary function.
Here's an example of an Objective-C category, containing a variadic
method that appends all the objects in a nil-terminated list of
arguments to an NSMutableArray instance:
#import <Cocoa/Cocoa.h>
#interface NSMutableArray (variadicMethodExample)
// This method takes a nil-terminated list of objects.
- (void)appendObjects:(id)firstObject, ...;
#end
#implementation NSMutableArray (variadicMethodExample)
- (void)appendObjects:(id)firstObject, ... {
id eachObject;
va_list argumentList;
if (firstObject) // The first argument isn't part of the varargs list,
{ // so we'll handle it separately.
[self addObject: firstObject];
// Start scanning for arguments after firstObject.
va_start(argumentList, firstObject);
while (eachObject = va_arg(argumentList, id)) // As many times as we can get an argument of type "id"
[self addObject: eachObject]; // that isn't nil, add it to self's contents.
va_end(argumentList);
}
}
#end
A solution that I use for debugging purposes is like
-(void) debug:(NSString*)format, ... {
if (level < MXMLogLevelDebug) return;
if(format == nil) return;
va_list args, args_copy;
va_start(args, format);
va_copy(args_copy, args);
va_end(args);
NSString *logString = [[NSString alloc] initWithFormat:format
arguments:args_copy];
NSString *funcCaller = #"";
NSArray *syms = [NSThread callStackSymbols];
if ([syms count] > 1) {
funcCaller = [syms objectAtIndex:1];
}
NSString *logMessage = [NSString stringWithFormat:#"%# DEBUG: %#", funcCaller, logString];
NSLog(#"%#",logMessage);
}
The side-effect that this can have is that you have to add a guard on the args to be sure is not NULL.
Since property named "age" would always have a selector named "age" as well, I could use respondsToSelector as this question suggests and that will tell me if a particular selector exists at runtime in any given object.
If a property named "age" exists, I can verify that. How could I know if that selector (the read method for that property) returns an object (id) or non-object (int)?
Is such type determination possible at runtime, or is the Objective-C way to always assume that someone implemented that method using the type I'm hoping it used, or can I also verify the return type?
This is using the latest Objective-C version (LLVM 4.1) in XCode 4.5.
Update: This is the utility-category-on-NSObject that I came up with:
- (NSString*) propertyType: (NSString*)propname
{
objc_property_t aproperty = class_getProperty([self class], [propname cStringUsingEncoding:NSASCIIStringEncoding] ); // how to get a specific one by name.
if (aproperty)
{
char * property_type_attribute = property_copyAttributeValue(aproperty, "T");
NSString *result = [NSString stringWithUTF8String:property_type_attribute];
free(property_type_attribute);
return result;
}
else
return nil;
}
While looking into this question I also wrote this handy-dandy utility method that
can list all the properties on this object:
- (NSArray*) properties;
{
NSMutableArray *results = [NSMutableArray array];
#autoreleasepool {
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList([self class], &outCount);
for (i = 0; i < outCount; i++) {
objc_property_t property = properties[i];
const char * aname=property_getName(property);
[results addObject:[NSString stringWithUTF8String:aname]];
//const char * attr= property_getAttributes(property);
//[results addObject:[NSString stringWithUTF8String:attr]];
}
if (properties) {
free(properties);
}
} // end of autorelease pool.
return results;
}
You could use class_copyPropertyList to get a list of properties declared in a class.
class_copyPropertyList
Describes the properties declared by a class.
And then property_getAttributes:
property_getAttributes
Returns the attribute string of an property.
Here you can find some more concrete hints and examples.
As a side note, the following statement:
Since property named "age" would always have a selector named "age" as well
is not correct, since a property can have custom getter and/or setter:
#property (nonatomic, getter=isImmediate) BOOL immediate;
EDIT:
Some sample code I found in another S.O. post:
const char * type = property_getAttributes(class_getProperty([self class], "myPropertyName"));
NSString * typeString = [NSString stringWithUTF8String:type];
NSArray * attributes = [typeString components separatedByString:#","];
NSString * typeAttribute = [attributes objectAtIndex:0];
NSString * propertyType = [typeAttribute substringFromIndex:1];
const char * rawPropertyType = [propertyType UTF8String];
if (strcmp(rawPropertyType, #encode(float)) == 0) {
//it's a float
} else if (strcmp(rawPropertyType, #encode(int)) == 0) {
//it's an int
} else if (strcmp(rawPropertyType, #encode(id)) == 0) {
//it's some sort of object
} else ....
One approach you can take, assuming you know the property name already, is to use the class_getProperty function. You can also use the property_copyAttributeValue() function to get just a particular attribute by name:
objc_property_t number_property = class_getProperty([MyClass class], "number");
char *number_property_type_attribute = property_copyAttributeValue(number_property, "T");
NSLog(#"number property type attribute = %s", number_property_type_attribute);
Will log:
2013-01-14 14:45:37.382 RuntimeFun[61304:c07] number property type
attribute = i
Assuming MyClass looks something like:
#interface MyClass : NSObject
#property (nonatomic) int number;
#end
#implementation MyClass
#end
One you have your type attribute string, you can then compare it to the various Objective-C type encodings. Once you're done with your comparison, be sure to call free() on your attribute string.
Please look at this code snipped
- (SoapRequest*)AddFlyData:(id)_target
action:(SEL)_action
sessionid:(int)sessionid
datasets:(FlyNetArrayOfDataSet*)datasets
{
if ([datasets isKindOfClass:[FlyNetArrayOfDataSet class]]) {
NSLog(#"Yeah");
} else {
NSLog(#"Not Yeah");
}
}
Why, when i look on my console, I get
2011-09-06 23:08:00.917 soap-test[2133:207] Not Yeah
I'm a beginner and I'm completely confused .. :s When I look in the Debugger, the variable type is SoapArray (who is the parent class of FlyNetArrayOfDataSet).
I used a method from SoapArray to initiate my instance of 'datasets', that means the class is automatically defined as Soap and not as FlyNetArrayOfDataSet ?!
Thank you
EDIT: I made a mistake, it's not NSArray but it inherits from SoapArray
This is the header file of the class FlyNetArrayOfDataSet
#import "Soap.h"
#interface FlyNetArrayOfDataSet : SoapArray
{
}
+ (NSMutableString*) serialize: (NSArray*) array;
#end
But that didn't explain me why isKindOfClass returns false ..
EDIT2: Ok I have the response of my question..
I used this method to initialize my instance
FlyNetArrayOfDataSet * arr = [FlyNetArrayOfDataSet arrayWithObject:data];
This is a static method of the superclass SoapArray that create an instance of SoapArray (Helper) .. but not an instance of FlyNetArrayOfDataSet (!)
Look at its implementation :
+ (id)arrayWithObjects:(id)firstObj, ...{
SoapArray* a = [SoapArray array];
id eachObject;
va_list argumentList;
if (firstObj) {
[a.items addObject: firstObj];
va_start(argumentList, firstObj);
while (eachObject = va_arg(argumentList, id)) {
[a.items addObject: eachObject];
}
va_end(argumentList);
}
return a;
}
If I initialize my instance like this
FlyNetArrayOfDataSet * arr = [[FlyNetArrayOfDataSet alloc] init];
It's work perfectly and the method isKindOfClass return true :-)
Suppose you have a class named "FlyNetArrayOfDataSet" which inherits from (=is a subclass of) NSArray.
If you instantiate a variable like:
FlyNetArrayOfDataSet *arr = [[FlyNetArrayOfDataSet alloc] init];
As you can see, I'm initializing the array with a method of NSArray. However, my "arr" object will be of kind FlyNetArrayOfDataSet, and NOT NSArray, because I called the FlyNetArrayOfDataSet class (see [FlyNetArrayOfDataSet arrayWithObject....).
NSLog(#"%d", [arr isKindOfClass:[FlyNetArrayOfDataSet class]]);
NSLog(#"%d", [arr isKindOfClass:[NSArray class]]);
Both will return "1", which means "true", because arr is an object of the FlyNetArrayOfDataSet class, which inherits from NSArray.
EDIT
Let's see if I can explain it better:
arr1 = [[FlyNetArrayOfDataSet alloc] init];
arr2 = [[NSArray alloc] init];
Both objects, arr1 and arr2, are created with the same method, which is defined in the class NSArray. However, in the first case the class which is being called is FlyNetArrayOfDataSet and in the second case is NSArray. Thus, arr1 will be an object of class FlyNetArrayOfDataSet, while arr2 will be of class NSArray.
The difference can be seen in this code:
NSLog(#"%d %d",
[arr1 isKindOfClass:[FlyNetArrayOfDataSet class]]
[arr1 isKindOfClass:[NSArray class]]
);
NSLog(#"%d %d",
[arr2 isKindOfClass:[FlyNetArrayOfDataSet class]]
[arr2 isKindOfClass:[NSArray class]]
);
The output of this code is:
1 1 ( = true true)
0 1 ( = false true)
that's because FlyNetArrayOfDataSet is a SoapArray and SoapArray is not a FlyNetArrayOfDataSet.
if datasets were an instance of SoapArray, you will see "Soap" in the following example:
- (SoapRequest*)addFlyData:(id)target
action:(SEL)action
sessionid:(int)sessionid
datasets:(FlyNetArrayOfDataSet*)datasets
{
if ([datasets isKindOfClass:[FlyNetArrayOfDataSet class]]) {
NSLog(#"Fly");
}
else if ([datasets isKindOfClass:[SoapArray class]]) {
NSLog(#"Soap");
}
else {
NSLog(#"???");
}
}
it's possible that an instance of SoapArray is also FlyNetArrayOfDataSet. the other possibilities are:
a SoapArray
subclass other than FlyNetArrayOfDataSet.
I need a way to pass a property and get the name assigned to it. Any suggestions?
#property (nonatomic, retain) MyObject *crazyObject;
NSString *str = SOME_WAY_TO_GET_PROPERTY_NAME(crazyObject);
// Above method should return #"crazyObject"
You can try this:
unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([self class], &propertyCount);
NSMutableArray * propertyNames = [NSMutableArray array];
for (unsigned int i = 0; i < propertyCount; ++i) {
objc_property_t property = properties[i];
const char * name = property_getName(property);
[propertyNames addObject:[NSString stringWithUTF8String:name]];
}
free(properties);
NSLog(#"Names: %#", propertyNames);
It's as simple as this...expanding upon what Chuck already mentioned:
#ifndef STR_PROP
#define STR_PROP( prop ) NSStringFromSelector(#selector(prop))
#endif
You then use it like so:
NSString *strProp = STR_PROP(myProperty);
Background
Keep in mind that properties are really just, to quote Apple, "a syntactical shorthand for declaring a class’s accessor methods." In fact, by itself, the #property declaration doesn't even work. Your #synthesize statement translates the #property into the equivalent of two methods:
- (void)setCrazyObject:(MyObject *)something;
- (MyObject *)crazyObject;
Which one is used depends on the context surrounding your self.crazyObject. (#synthesize also creates a matching instance variable if you didn't do it yourself.) The offshoot of all this is that you can't really translate to and from a property with one single method.
Proposed Solution
You can use what Apple already provides:
NSString *foo = NSStringFromSelector(#selector(myClassProperty));
Or do something custom:
Given that self.crazyObject really translates to either [self crazyObject] or [self setCrazyObject:foo] by the time your code is running, ou'll probably need two methods, like:
- (NSString *)setterStringForProperty:(SEL)prop;
- (NSString *)getterStringForProperty:(SEL)prop;
You might then want at least 2 companion methods such as:
- (SEL)setterForPropertyName:(NSString *)propString;
- (SEL)getterForPropertyName:(NSString *)propString;
Within these methods, you can use the Foundation functions NSStringFromSelector and NSSelectorFromString to convert back and forth between SEL and NSString. Use whatever string manipulations you like to convert back and forth between your setter string (setCrazyObject) and your property name (crazyObject).
A complete solution is hard to provide without knowing the exact use case, but hopefully this provides some more clues for anyone trying to accomplish something similar. There might even be some useful things made possible by combining this approach with Oscar's answer.
Here is a function that returns the name of an ivar, so basically it not only returns the properties but any ivar of the class. I haven't found a way to get the property directly so I used the ivar trick.
#import <objc/objc.h>
/// -----
- (NSString *)nameOfIvar:(id)ivarPtr
{
NSString *name = nil;
uint32_t ivarCount;
Ivar *ivars = class_copyIvarList([self class], &ivarCount);
if(ivars)
{
for(uint32_t i=0; i<ivarCount; i++)
{
Ivar ivar = ivars[i];
id pointer = object_getIvar(self, ivar);
if(pointer == ivarPtr)
{
name = [NSString stringWithUTF8String:ivar_getName(ivar)];
break;
}
}
free(ivars);
}
return name;
}
After searching and debugging i find solution for me...
Added #import <objc/runtime.h>
Methods object_getIvar(id obj, Ivar ivar) send bad access and app crashes. i modify some code and it worked great:
+(NSString*)stringWithProperty:(id)property withClass:(id)controller
{
NSString *name = nil;
uint32_t ivarCount;
Ivar *ivars = class_copyIvarList([controller class], &ivarCount);
if(ivars)
{
for(uint32_t i=0; i<ivarCount; i++)
{
Ivar ivar = ivars[i];
name = [NSString stringWithUTF8String:ivar_getName(ivar)];
if ([controller valueForKey:name] == property)
{
break;
}
}
free(ivars);
}
return name;
}
Modifying the solution, it works when your object is allocated already, otherwise it returns nil:-
NSString * NSStringFromProperty(NSObject* property, NSObject* class)
{
unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([class class], &propertyCount);
NSString *name = nil;
for (unsigned int i = 0; i < propertyCount; ++i)
{
name = [NSString stringWithUTF8String:property_getName(properties[i])];
NSObject *object = [class valueForKey:name];
if (object != nil && object == property)
{
break;
}
else
{
name = nil;
}
}
free(properties);
return name;
}
You can use
NSString *str = NSStringFromSelector(#selector(crazyObject));
The good thing about this approach is that:
Xcode will autocomplete word crazyObject for you.
When later on you will change the property name from crazyObject to myCrazyObject, Xcode will add a warning saying "unrecognized selector!" -- pretty good for debugging.
I use this method so often, that I even created a function, which allows to write less letters:
NSString * __nonnull sfs(SEL __nonnull theSelector)
{
if (!theSelector)
{
abort();
}
return NSStringFromSelector(theSelector);
}
Now your final solution can look like this:
NSString *str = sfs(#selector(crazyObject));
From Get property name as string, without using the runtime reference library, just define:
#define propertyKeyPath(property) (#""#property)
#define propertyKeyPathLastComponent(property) [[(#""#property) componentsSeparatedByString:#"."] lastObject]
And then you can do something like this:
NSLog(#"%#", propertyKeyPathLastComponent(appleStore.storeLocation.street)); //result: street
You may check my approach at Gist to get the string for a property with autocompletion and compile-time check.
How to use:
Get the property name for a class:
#interface AnyClass : NSObject
#property (strong) NSData *data;
#end
// == My approach ==
// C string for a class
PropertyNameForClass(AnyClass, data); // ==> "data"
// NSString for a class
PropertyStringForClass(AnyClass, data); // ==> #"data"
// Bad approach (no autocompletion; no compile-time check):
NSString *propertyName = #"data";
Get the property name for a protocol:
#protocol AnyProtocol
#property (strong) NSDate *date;
#end
// C string for a protocol
PropertyNameForProtocol(AnyProtocol, date); // ==> "date"
// NSString for a protocol
PropertyStringForProtocol(AnyProtocol, date); // ==> #"date"
Unconventional, hacky, ugly, late, but... as strong-named as it gets and works like a charm:
#define SOME_WAY_TO_GET_PROPERTY_NAME(p) p == p ? [[[[[[[NSString alloc] initWithCString:#p encoding:NSUTF8StringEncoding] componentsSeparatedByString:#"."] lastObject] componentsSeparatedByString:#" "] lastObject] stringByReplacingOccurrencesOfString:#"]" withString:#""] : #""
Sample usage:
NSLog(SOME_WAY_TO_GET_PROPERTY_NAME(self.customer.surname)); // surname
NSLog(SOME_WAY_TO_GET_PROPERTY_NAME([[self customer] birthDate])); // birthDate
...
Say I have my class
#interface Person : NSObject { NSString *name; }
I need to get the name of NSString's within my class
Person *person = [[Person alloc] init];
NSLog(#"Name of variable %s\n", _NameofVariable_(person->name));
Thanks for the answers, here's the solution I came up from the replies
//returns nil if property is not found
-(NSString *)propertyName:(id)property {
unsigned int numIvars = 0;
NSString *key=nil;
Ivar * ivars = class_copyIvarList([self class], &numIvars);
for(int i = 0; i < numIvars; i++) {
Ivar thisIvar = ivars[i];
if ((object_getIvar(self, thisIvar) == property)) {
key = [NSString stringWithUTF8String:ivar_getName(thisIvar)];
break;
}
}
free(ivars);
return key;
}
As easy as
#define VariableName(arg) (#""#arg)
Then you do:
NSObject *obj;
NSString *str = VariableName(obj);
NSLog(#"STR %#", str);//obj
You can get the names of a class's instance variables with the Objective-C runtime API function class_copyIvarList. However, this is rather involved, rarely done and almost never the best way to accomplish something. If you have a more specific goal in mind than mere curiosity, it might be a good idea to ask about how to accomplish it in Objective-C.
Also, incidentally, person.name doesn't specify an instance variable in Objective-C — it's a property call. The instance variable would be person->name.
You might use preprocessor stringification and a bit of string twiddling:
NSUInteger lastIndexAfter(NSUInteger start, NSString *sub, NSString *str) {
NSRange found = [str rangeOfString:sub options:NSBackwardsSearch];
if(found.location != NSNotFound) {
NSUInteger newStart = NSMaxRange(found);
if(newStart > start)
return newStart;
}
return start;
}
NSString *lastMember(NSString *fullName) {
if(!fullName) return nil;
NSUInteger start = 0;
start = lastIndexAfter(start, #".", fullName);
start = lastIndexAfter(start, #"->", fullName);
return [fullName substringFromIndex: start];
}
#define NSStringify(v) (##v)
#define _NameofVariable_(v) lastMember(NSStringify(v))
If the person object is exposed as a property of the class, you can use objc_msgSend to get the value.
So, if you could access person using
[object person]
You could also do
objc_msgSend(object, "person")
For more details on message sending, including how to pass arguments to methods, see the Objective-C Runtime Programming Guide section on Messaging
The following works as a macro:
#define STRINGIZE(x) #x