I am on the project with Vue.js, and it's the first time I see that type of thing #property etc. Can anyone explain to me what this thing is?
P.S. with global search I cannot find references in my project folder, so don't know where it's derived from
I just tried to search the property name with Ctrl+Shift+F inside the project folder. That's about it. Just want to know something about this pattern.
It's just documenting the component arguments/properties.
From the docunentation:
If your event returns arguments/properties use the #property tag to describe them
/**
* Triggers when the number changes
*
* #property {number} newValue new value set
* #property {number} oldValue value that was set before the change
*/
this.$emit('change', newValue, oldValue)
Related
I want to deffine a bool variable and set default value for it. I can do this
First
#implementation ViewController1
BOOL var1 = false;
Second
And I can add it in ViewController1.h file
#property (nonatomic, assign) BOOL var1
Is it possible to set default value in second way
What is difference between these two?
First way is global. That means you have potential to disturb other library or framework that you use in your app.
Second way is the correct way to do it but of course it limits to only your class. Also memorywise, is better.
Also, if you want "global" variable, use singleton. :D
What's going on inside the brackets when variables are declared inside the public interface of the .h file? What is a case that you would do something like this? It seems to me you should just make properties that are backed by these variables public and remove the variables from the .h file.
#interface GSFullscreenAdViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate>
{
/**
* This view controller's view.
*/
GSFullscreenAdView * m_adView;
/**
* The ad that is currently fetched or displaying. Resets to nil on ad dismissal.
*/
GSFullscreenAd * m_currentAd;
/**
* The view controller that this GSFullscreenAdViewController is being
* displayed from.
*/
UIViewController * m_parentViewController;
/**
* Whether the ad is currently displaying
*/
BOOL m_isDisplaying;
/**
* Whether the ad is currently animating onto the screen
*/
BOOL m_isPresenting;
/**
* Whether the ad is in the process of being dismissed
*/
BOOL m_isDismissing;
UIImagePickerController * m_imagePickerController;
}
#property (readonly) GSFullscreenAdView * adView;
#property (readonly) BOOL isDisplaying;
#property (nonatomic) BOOL allowOrientationChange;
The ability to declare your instance variables in your #implementation section is actually a relatively new addition to Objective-C. Before Xcode 4.2 (released 2011/10/12), you could only declare your instance variables in the #interface section. Perhaps the code you're looking at was written before Xcode 4.2 (or later) was in wide use.
Check it yourself in the Objective-C Feature Availability Index.
Nowadays just declaring a property would do for most cases. For older versions of objective-c the corresponding iVar had to be declared manually. For doing so the iVar had to be declared within curly brackets before the property was declared.
Even today you may want so associate a property with a given iVar (by naming the iVar in the #synthezise statement. However, for that it should be sufficient to declare the iVar within curly brackets following the #interface statement. In those cases you could declare them within brackets following a second #interface statement in the .m file.
Well, it still works. Some oder tutorials still use this pattern. You or your team/company may still use older code that does this.
And finally it is hard, sometimes, to overcome an old peculiar :-)
I often have a hard time deciding if certain data should be exposed through a property or a method. You can say "use properties for object state", but that's not very satisfying. Take this example for instance:
- (NSString *)stringOne
{
return _stringOne;
}
- (NSString *)stringTwo
{
return _stringTwo;
}
- (NSString *)mainString
{
return [_stringOne length] > 0 ? _stringOne : _stringTwo;
}
It's clear that stringOne and stringTwo should be properties because they are clearly object state. It's not clear, however, if mainString should be a property. To the end user mainString acts like state. To your object, mainString is not state.
This example is contrived but hopefully you get the idea. Yes, properties are nothing more than a convenient way to create getters and setters but they also communicate something to the user. Does anyone have decent guidelines for deciding when to use a property vs a method.
Hiding the split between "true" state (string1 and string2 in your example) and "dynamic" state (mainString) is, I would say, exactly what properties are for.
The canonical example would probably be an object that represents a person, with given and family names as "state". A third piece of state, "full name" can be presented from those two pieces, but clients have absolutely no reason to know whether the full name is constructed on demand, or is created and stored when both of its pieces are set. It simply doesn't matter.
Properties are an interface -- what bits of data does this class provide to its clients (and what can the clients configure about the class)? The implementation of each property is encapsulated and does not affect its status as a property.
In ObjC, of course, we use methods to access properties. Other methods, however, represent actions that an object can take, possibly being passed some piece of data to operate on.
Another consideration to take into account : do you want to store the value of the property ? (via NSCoding or in Core Data for example)
I guess you NEED to create properties for things you need to "save" (in "encodeWithCoder" for instance. Deciding what you want to put in encodeWithCoder could help you decide which way you want to define things).
For things you don't need to save and can recalculate easily, you have the choice between a method and a readonly property (which is equivalent under the hood : a readonly property only creates a getter accessor method, and does not have an instance variable to back it). So that's more a question of style.
Speaking of style, if you use dot notation for properties only (as I do), you'd maybe wonder :
- do I want to access the full name as foo.fullName, and not make a difference with other properties like foo.firstName and foo.lastName ?
- or do you want to make a difference by accessing the full name with [foo fullName], showing to the world that this is calculated ?
I created an app for following stock quotes, and the model was inspired from an example in the Big Nerd Ranch book about Objective C (good read, by the way).
Here is how properties and methods are defined :
// properties
#property (nonatomic, copy) NSString *name;
#property (nonatomic, copy) NSString *symbol;
#property (nonatomic, copy) NSString *currency;
#property (nonatomic, copy) NSString *market;
#property (nonatomic) int numberOfShares;
#property (nonatomic) double purchaseSharePrice;
#property (nonatomic) double currentSharePrice;
// Stock Calculation methods
- (double)costInLocalCurrency; // purchaseSharePrice * numberOfShares
- (double)valueInLocalCurrency; // currentSharePrice * numberOfShares
- (double)gainOrLossInLocalCurrency // valueInLocalCurrency - costInLocalCurrency
You can see that they are clearly distinguished.
The BNR does not use dot notation at all in their book, so it would all look the same : [foo currentSharePrice] or [foo valueInLocalCurrency], but as I use dot notation for properties, I would make a difference in style between foo.currentSharePrice and [foo valueInLocalCurrency].
Hope this is helpful.
By design, you should always respect the end user - if you think it's object state for the user of your class (which it apparently is), then go ahead and make a property out of it.
I am just learning OOP from a book I picked up (Big Nerd Ranch), and it just went through the getter and setter chapter. I would just like to clarify I understand what I have just done. Instead of creating a method to set the value of an instance, and then another method to extract the value and display it, I create use the #property and #synthesize syntax to define both methods.
Instead of doing this:
-(void) setHeightOfObject:(int)h;
-(void) setWeightOfObject:(float)w;
-(int) heightOfObject;
-(float) weightOfObject;
and defining it like this:
- (int)heightOfObject
{
return heightOfObject;
}
- (void)setHeightOfObject:(int)h
{
heightInMeters = h;
}
- (float)weightOfObject
{
return weightOfObject;
}
- (void)setWeightOfObject:(float)w
{
weightOfObject = w;
}
I would do this with getter and setters in the .h file:
#property int heightOfObject;
#property float weightOfObject;
And then go to my .m file and link it:
#synthesize heightInMeters, weightOfObject;
This then gives me the ability to set the value of my object, and then get it if I need it printed? I know this is an important concept and I want to make sure I have the proper grasp of it.
You are correct. The #synthesize essential expands out to the implementation you wrote while compiling.
Since writing getters and setters is boring and repetitive (and most objects have a bunch of properties you'd want getters and setters for) having this little shortcut makes you spend less time on boilerplate code and more time implementing something interesting.
If you'd like more detailed information about objective-c's properties, you can have a look at the programming guide (although this might be somewhat unnecessarily detailed for you at this point).
There are two parts to what you are achieving by using #property and #synthesize.
#property tells the compiler that it should allow you to use dot syntax to call the accessors of heightOfObject and weightOfObject. So doing this
int height = myObject.heightOfObject;
myObject.weightOfObject = 10;
becomes legal code and is exactly equivalent to this:
int height = [myObject heightOfObject];
[myObject setWeightOfObject:10];
You can use #property without #synthesize, in which case you must implement the accessors exactly as you have done in your question.
Using #synthesize tells the compiler that it should generate the accessors for you and it will also generate the instance variables themselves if your runtime supports it (e.g. on iOS and 64-bit OS X).
Property and synthesise were introduced in Objective C 2.0 in order to provide a straightforward way to create getters and setters.
Check this link it will be of help:
http://cocoacast.com/?q=node/103
You not only get getters and setters. You also get a neat syntax: self.heightOfObject which you can assign to or read from.
#property has a lot of settings though so you might want to read in detail. In particular you can control whether you need both read and write access or only one of them.
I'm currently using the iOS 5 SDK trying to develop my app.
I'm trying to make an NSString a property, and then to synthesize it in the .m file (I have done this before with no issues). Now, I came across this: "Semantic Issue: Property's synthesized getter follows Cocoa naming convention for returning 'owned' objects."
This is my code:
.h
#interface ViewController : UIViewController {
NSString *newTitle;
}
#property (strong, nonatomic) NSString *newTitle;
.m
#synthesize newTitle;
Does anyone have a clue how I could fix this?
Thanks!!
My guess is that the compiler version you’re using follows the memory management rules for declared properties, too — more specifically, for declared properties’ accessors:
You take ownership of an object if you create it using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy”.
A property named newTitle, when synthesised, yields a method called -newTitle, hence the warning/error. -newTitle is supposed to be a getter method for the newTitle property, however naming conventions state that a method whose name begins with new returns an object that’s owned by the caller, which is not the case of getter methods.
You can solve this by:
Renaming that property:
#property (strong, nonatomic) NSString *theNewTitle;
Keeping the property name and specifying a getter name that doesn’t begin with one of the special method name prefixes:
#property (strong, nonatomic, getter=theNewTitle) NSString *newTitle;
Keeping both the property name and the getter name, and telling the compiler that, even though the getter name starts with new, it belongs to the none method family as opposed to the new method family:
#ifndef __has_attribute
#define __has_attribute(x) 0 // Compatibility with non-clang compilers
#endif
#if __has_attribute(objc_method_family)
#define BV_OBJC_METHOD_FAMILY_NONE __attribute__((objc_method_family(none)))
#else
#define BV_OBJC_METHOD_FAMILY_NONE
#endif
#interface ViewController : UIViewController
#property (strong, nonatomic) NSString *newTitle;
- (NSString *)newTitle BV_OBJC_METHOD_FAMILY_NONE;
#end
Note that even though this solution allows you to keep newTitle as both the property name and the getter name, having a method called -newTitle that doesn’t return an object owned by the caller can be confusing for other people reading your code.
For the record, Apple have published Transitioning to ARC Release Notes, in which they state:
You cannot give a property a name that begins with new or copy.
They’ve already been notified that their statement is not quite accurate: the culprit is the getter method name, not the property name.
Edit 17 Jan 2015: I’ve just noticed a recent commit to Clang that suggests option 3 above (using objc_method_family(none)), including a fix-it, for the general case where a property name matches one of the special method family prefixes. Xcode will likely incorporate this change eventually.
Unacceptable Object Names
newButton
copyLabel
allocTitle
Acceptable Object Names
neueButton
mCopyLabel
_allocTitle
#arc #auto-synthesized #xcode-4.6.1
** EDIT **
Apparently you can't use mutableCopy either.
The name of the member starting with new is what triggers the warning. Change the name to editedTitle and the warning will go away. I was unable to find documentation confirming this but through testing was able to determine that member variables that begin with 'new' aggravate the compiler.
ARC does not allow to use "New...." in property name. but you can use "newTitle" by changing getter name.
#property (nonatomic, strong, getter=theNewTitle) NSString *newTitle;
It doesn't look like what Bavarious was suggesting was what you wanted to do. All you want to do is declare an instance variable NewTitle and then synthesize the property. We used to have to declare the instance variable and property. No more.
Now, I believe the right way of doing this is the following:
.h
#interface ViewController : UIViewController
#property (nonatomic, strong) NSString *newTitle;
.m
#synthesize newTitle = _newTitle; // Use instance variable _newTitle for storage
The instance variable for the property newTitle is synthesized. You don't want your instance variable to be the same as your property - too easy to make mistakes.
See Example: Declaring Properties and Synthesizing Accessors
In CoreData if you use "new..." in attribute (compile normally) it will crash randomly with a "bad access" exception.
There is no crash log and the line shown with the "All Exceptions Breakpoint" will not help you at all.
Writing a setter manually with the name same as the property's removed this warning.
NS_RETURNS_NOT_RETAINED is used to solve the naming problem.
#property (nonatomic, copy) NSString *newTitle NS_RETURNS_NOT_RETAINED;
We can find its definition as follows:
#define NS_RETURNS_NOT_RETAINED __attribute__((ns_returns_not_retained))
The 'ns_returns_not_retained' attribute is the complement of 'ns_returns_retained'. Where a function or method may appear to obey the Cocoa conventions and return a retained Cocoa object, this attribute can be used to indicate that the object reference returned should not be considered as an "owning" reference being returned to the caller. The Foundation framework defines a macro NS_RETURNS_NOT_RETAINED that is functionally equivalent to the one shown below.
Besides the issue that you should/can't use "new" in front of you property names, let say one more thing: Try to avoid "new" in front of names in general. "New" is dependent on time. Currently it is new for you, but some time later you maybe want to implement something new again. So using "new" in names is always bad. Try to think this way: In the programming world, "new" is always creating something: a new instance of something.
In your case when you want to assign a different title then the current name your property titleReplacement.
One more thing: Try to name functions and methods with the verb first, like setSomething or getSomething.
But in properties try to name the object first, like heightMinimum, heightMaximum, etc. -> when you use your inspector when you are coding, you always looking for objects. Try it out. ;-)
try this:-
#property (nonatomic,retain) NSString *newTitle;