Extract
Extract variable
If you come across an expression that is hard to understand, or it is duplicated in several places throughout you code, you can place the result of such expression or its part into a separate variable using the Extract Variable refactoring ⌃⌥V.
Perform the Extract Variable refactoring
In the editor, select an expression or its part you want to extract or just place the caret within this expression.
Press ⌃⌥V or select from the main menu.
If you've placed the caret within the expression, AppCode will offer you a list of potential code selections. Choose the desired selection from the list.
If the expression you want to extract is used multiple times, you can select whether you want to replace all occurrences or just the current one.
- If necessary, change the default variable name and use additional options:
For Swift: check Declare with 'var' if you want to declare a variable (with
var). Deselect this checkbox to declare a constant (withlet). Uncheck Specify type explicitly if you don't want to add a data type to the variable declaration.For Objective-C: check Declare const to declare a new reference as a constant (with
const):
Press ⏎.
Code example
| Before | After |
|---|---|
- (void)performLogin {
// self.textFieldEmail.text will be extracted
// to the email variable
BOOL isEmailValid = [self.emailValidator isEmailValid:self.textFieldEmail.text];
if (isEmailValid == NO) {
[self.loginModel loginWithEmail:self.textFieldEmail.text];
}
}
|
- (void)performLogin {
// Extracted variable
NSString *email = self.textFieldEmail.text;
BOOL isEmailValid = [self.emailValidator isEmailValid:email];
if (isEmailValid == NO) {
[self.loginModel loginWithEmail:email];
}
}
|
| Before | After |
|---|---|
private func performLogin() {
// email: self.textFieldEmail.text ?? will be extracted
// to the email variable
let isEmailValid = self.emailValidator.isEmailValid(email: self.textFieldEmail.text ?? "")
if (isEmailValid == true) {
self.loginModel.login(email: self.textFieldEmail.text ?? "")
}
}
|
private func performLogin() {
// Extracted variable
let email = self.textFieldEmail.text ?? ""
let isEmailValid = self.emailValidator.isEmailValid(email: email)
if (isEmailValid == true) {
self.loginModel.login(email: email)
}
}
|
Extract closure
The Extract Closure refactoring creates a closure based on the selected chunk of code.
The refactoring is available for Swift only.
Perform the Extract Closure refactoring
In the editor, select an expression which you want to extract into a closure.
Press ⌃⌥⇧T and select Closure. Alternatively, select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
In the dialog that opens, type the name of the new closure and change the parameter names and types if necessary.
Press ⏎.
Code example
| Before | After |
|---|---|
private func performLogin() {
let emailField = self.textFieldEmail
let email = emailField?.text ?? ""
let isEmailValid = self.emailValidator.isEmailValid(email: email)
// This expression will be extracted to closure
emailField?.textColor = isEmailValid ? UIColor.black : UIColor.red
// ...
}
|
private func performLogin() {
let emailField = self.textFieldEmail
let email = emailField?.text ?? ""
let isEmailValid = self.emailValidator.isEmailValid(email: email)
// Extracted closure
let setFieldStyle = { (textField: UITextField?, islValid: Bool) in
textField?.textColor = islValid ? UIColor.black : UIColor.red
}
setFieldStyle(emailField, isEmailValid)
// ...
}
|
Extract constant
The Extract Constant refactoring helps you avoid using hardcoded constants without any explanations about their values or purpose.
The refactoring is available for Objective-C only.
Perform the Extract Constant refactoring
In the editor, select an expression or declaration of a variable you want to replace with a constant.
Press ⌃⌥C to introduce a constant or select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
Select a name for the constant from the list of suggestions that opens or type a new one.
Check the Put to header checkbox if you want the constant to be moved to the header file.
Uncheck the Declare static checkbox if you don't want the constant to be declared as
static.Press ⏎.
Code example
| Before | After |
|---|---|
@implementation PasswordValidator
+ (BOOL)isPasswordValid:(NSString *)password {
// 4 will be extracted to a constant
return password.length > 4;
}
@end
|
// Extracted constant
static const int kMinPasswordLength = 4;
@implementation PasswordValidator
+ (BOOL)isPasswordValid:(NSString *)password {
return password.length > kMinPasswordLength;
}
@end
|
Extract instance variable
With the Extract Instance Variable refactoring, you can place an expression into an instance variable.
The refactoring is available for Objective-C only.
Perform the Extract Instance Variable refactoring
In the editor, select an expression you want to replace with an instance variable.
Press ⌃⌥F or select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
Select a name for the instance variable from the list of suggestions that opens or type a new one.
If you want to create a property for the variable or declare it in the interface, select the corresponding checkboxes in the popup that opens.
Press ⏎.
Code example
| Before | After |
|---|---|
@implementation LoginViewController {
}
- (void)performLogin {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
// success will be extracted to
// an instance variable
if (success) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
|
@implementation LoginViewController {
// Extracted instance variable
BOOL _loginSuccessful;
}
- (void)performLogin {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
_loginSuccessful = success;
if (_loginSuccessful) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
|
Extract property
The Extract Property refactoring lets you move expressions and local declarations to properties.
The refactoring is available for Objective-C only.
Perform the Extract Property refactoring
In the editor, select the expression or declaration you want to replace with a property.
Press ⌃⌥E or select Refactor | Extract/Introduce | Property from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
Select a name for the property from the list of suggestions that opens or type a new one.
If you want the property to be generated in a private category, select the Put to private category checkbox. Otherwise, the property will be declared in the header file.
Press ⏎.
Code example
| Before | After |
|---|---|
@interface LoginViewController ()
// ...
@end
@implementation LoginViewController {
}
- (void)performLogin {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
// success will be extracted to
// a property
if (success) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
|
@interface LoginViewController ()
// ...
// Extracted property
@property(nonatomic) BOOL loginSuccessful;
@end
@implementation LoginViewController {
}
- (void)performLogin {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
self.loginSuccessful = success;
if (self.loginSuccessful) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
|
Extract parameter
The Extract Parameter refactoring is used to add a new parameter to a method declaration and to update the method calls accordingly.
The refactoring is available for Objective-C only.
Perform the Extract Parameter refactoring
In the editor, place a cursor within the expression that you want to introduce as a parameter
Press ⌃⌥P or select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
If you want to declare the generated parameter as a constant, check Declare const in the popup that opens.
Press ⏎.
Code example
| Before | After |
|---|---|
@implementation Greeting {
}
- (NSString *)generateGreeting{
// This expression will be converted to
// the method's parameter
NSString *userName = @"Bob";
return [NSString stringWithFormat:@"Hello %@", userName];
}
- (void)print {
// Method's call
NSLog(@"%@", [self generateGreeting]);
}
@end |
@implementation Greeting {
}
// Method with the new parameter
- (NSString *)generateGreeting:(NSString *)userName {
return [NSString stringWithFormat:@"Hello %@", userName];
}
- (void)print {
// Method's call
NSLog(@"%@", [self generateGreeting:@"Bob"]);
}
@end
|
Extract define
The Extract Define refactoring method defines the selected set of tokens as a macro using the #define directive and replaces the set of tokens with the macro call in the code. The macro definition can be located in the current file or moved to the related header file.
The refactoring is available for Objective-C only.
Perform the Extract Define refactoring
In the editor, select the expression you want to replace with a macro call.
Press ⌃⌥D or select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
If more than one occurrence of the selected expression is found, AppCode will suggest replacing all the occurrences or just the selected one. Select the desired option from the list that opens.
Select a name for the macro from the list of suggestions that opens or type a new one.
Select Put to header if you want to move the macro definition to the header file.
Code example
| Before | After |
|---|---|
@implementation Screen{
}
- (CGPoint)getScreenCenter {
// [UIScreen mainScreen].bounds.size will be extracted
return CGPointMake(0.5 * [UIScreen mainScreen].bounds.size.width,
0.5 * [UIScreen mainScreen].bounds.size.height);
}
@end
|
// Extracted #define
#define SCREEN_SIZE [UIScreen mainScreen].bounds.size
@implementation Screen{
}
- (CGPoint)getScreenCenter {
return CGPointMake(0.5 * SCREEN_SIZE.width,
0.5 * SCREEN_SIZE.height);
}
@end
|
Extract typedef
The Extract Typedef refactoring changes the selected declaration of a type to a typedef definition. You can apply Extract Typedef when actual declaration is cumbersome, potentially confusing, or likely to vary from one implementation to another, or just to make code presentation more clear and readable.
The refactoring is available for Objective-C only.
Perform the Extract Typedef refactoring
In the editor, select the type declaration to be re-declared.
Press ⌃⌥K or select from the main or context menu.
If there are several expressions available for extracting, select the required one from the list that opens and press ⏎.
If more than one occurrence of the selected expression is found, AppCode will suggest replacing all the occurrences or just the selected one. Select the desired option from the list that opens.
Select a name for the typedef from the list of suggestions that opens or type a new one.
Select Put to header if you want to move the typedef definition to the header file.
Code example
| Before | After |
|---|---|
@interface LoginModel : NSObject
- (void)loginWithEmail:(NSString *)email
password:(NSString *)password
// void (^)(BOOL success) will be extracted to a typedef
completion:(void (^)(BOOL success))completion;
@end
|
// Extracted typedef
typedef void (^LoginModelCompletion)(BOOL);
@interface LoginModel : NSObject
- (void)loginWithEmail:(NSString *)email
password:(NSString *)password
completion:(LoginModelCompletion)completion;
@end
|
Extract method
The Extract Method refactoring lets you take a code fragment that can be grouped together, move it into a separated method and replace the old code with a call to the method.
The Extract Method refactoring has the following limitations:
Refactoring does not work with multiple output values in the automatic mode. You have to change your code before applying the refactoring, for example, you may introduce a special data-class that contains all output values.
Refactoring does not work for a code fragment which conditionally returns from the containing method and is not placed at the end of it.
To reverse the Extract Method refactoring, press ⌃⌥N to invoke the Inline refactoring.
Perform the Extract Method refactoring
Select a code fragment you want to extract to a method.
Press ⌃⌥M or from the main or context menu, select .
In the dialog that opens, configure method options, such as visibility, parameter names, selector parts (for Objective-C), and so on. You can also change a name of the method if you need.
Click Extract.
Code example
| Before | After |
|---|---|
- (void)setupUI {
// ...
// This code will be extracted to a method
self.buttonLogin.layer.borderColor = [[UIColor blackColor] CGColor];
self.buttonLogin.layer.borderWidth = 1.0;
[self.buttonLogin setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[self.buttonLogin setTitle:@"Login" forState:UIControlStateNormal];
}
|
- (void)setupUI {
// ...
// Extracted method's call
[self setupLoginButton];
}
// Extracted method
- (void)setupLoginButton {
self.buttonLogin.layer.borderColor = [[UIColor blackColor] CGColor];
self.buttonLogin.layer.borderWidth = 1.0;
[self.buttonLogin setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[self.buttonLogin setTitle:@"Login" forState:UIControlStateNormal];
}
|
| Before | After |
|---|---|
private func setupUI() {
// ...
// This code will be extracted to a method
self.buttonLogin.layer.borderColor = UIColor.black.cgColor
self.buttonLogin.layer.borderWidth = 1.0
self.buttonLogin.setTitleColor(UIColor.black, for: .normal)
self.buttonLogin.setTitle("Login", for: .normal)
}
|
private func setupUI() {
// ...
// Extracted method's call
setupLoginButton()
}
// Extracted method
private func setupLoginButton() {
self.buttonLogin.layer.borderColor = UIColor.black.cgColor
self.buttonLogin.layer.borderWidth = 1.0
self.buttonLogin.setTitleColor(UIColor.black, for: .normal)
self.buttonLogin.setTitle("Login", for: .normal)
}
|
Extract block parameter
With the Extract Block Parameter refactoring, you can create a block declaration based on the selected chunk of code within a method. As a result, the created block is passed as a parameter to this method, and all existing usages of this method are changed accordingly.
The refactoring is available for Objective-C only.
Perform the Extract Block Parameter refactoring
In the editor, select a chuck of code (within a method) which you want to replace with a block declaration.
Select from the main or context menu.
In the dialog that opens, type the name of the block. If necessary, add/delete parameters, edit parameter names and types, and click Extract.
Code example
| Before | After |
|---|---|
- (void)performLogin {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
// This code block will be extracted
if (success) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
- (IBAction)buttonLoginPressed:(id)sender {
// Method's call
[self performLogin];
}
|
- (void)performLogin:(void (^)(BOOL))completion {
// ...
[self.loginModel loginWithEmail:email password:password completion:^(BOOL success) {
// Extracted block
completion(success);
}];
}
- (IBAction)buttonLoginPressed:(id)sender {
// Method's call with the extracted block
// as a parameter
[self performLogin:^(BOOL controller) {
if (controller) {
[self showAlertLoginSuccess];
} else {
[self showAlertLoginFailed];
}
}];
}
|
Extract superclass
The Extract Superclass refactoring enables extracting certain members of a class into a newly created superclass.
The refactoring is available for Objective-C only.
Perform the Extract Superclass refactoring
Select the desired class in the editor.
Select from the main or context menu.
In the dialog that opens, type the name of the new superclass, select the members that you want to move to the superclass, and click Extract.
Code example
| Before | After |
|---|---|
// All methods of the Dog class
// will moved to a superclass
// Dog.h
@interface Dog : NSObject
- (void)run;
- (void)eat;
@end
// Dog.m
@implementation Dog {
}
-(void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end
|
// New superclass
// Animal.h
@interface Animal : NSObject
- (void)run;
- (void)eat;
@end
// Animal.m
@implementation Animal {
}
-(void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end
// The Dog class is now a subclass
// of the Animal class
// Dog.h
@interface Dog : Animal
@end
// Dog.m
@implementation Dog {
}
@end
|
Extract subclass
The Extract Subclass refactoring enables extracting certain members of a class into a newly created subclass.
The refactoring is available for Objective-C only.
Perform the Extract Subclass refactoring
Select the desired class it in the editor.
Select from the main or context menu.
In the dialog that opens, type the name of the new subclass, select the members that you want to move there, and click Extract.
Code example
| Before | After |
|---|---|
// Animal.h
@interface Animal : NSObject
- (void)meow;
- (void)run;
- (void)eat;
@end
// Animal.m
@implementation Animal {
}
// This method will be moved
// to a subclass
- (void)meow{
NSLog(@"Meow!");
}
- (void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end
|
// New subclass
// Cat.h
@interface Cat : Animal
- (void)meow;
@end
// Cat.m
@implementation Cat {
}
- (void)meow{
NSLog(@"Meow!");
}
@end
// The Animal class
// Animal.h
@interface Animal : NSObject
- (void)run;
- (void)eat;
@end
// Animal.m
@implementation Animal {
}
- (void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end
|
Extract protocol
With the Extract Protocol refactoring you can create a new protocol based on the members of the current class.
The refactoring is available for Objective-C only.
Perform the Extract Protocol refactoring
Select the desired class in the editor.
Select from the main or context menu.
In the dialog that opens, type the name of the new protocol, select the members that you want to move there, and click Extract.
Code example
| Before | After |
|---|---|
// Dog.h
@interface Dog
// This method will be extracted
// to a protocol
- (void)swim;
- (void)run;
- (void)eat;
@end
// Dog.m
@implementation Dog {
}
- (void)swim {
NSLog(@"I am swimming");
}
- (void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end
|
// New protocol
// Swimmable.h
@protocol Swimmable <NSObject>>
- (void)swim;
@end
// Dog.h
@interface Dog <Swimmable>
- (void)run;
- (void)eat;
@end
// Dog.m
@implementation Dog {
}
- (void)swim {
NSLog(@"I am swimming");
}
- (void)run {
NSLog(@"I am running");
}
- (void)eat {
NSLog(@"I am eating");
}
@end |
Extract category
With the Extract Category refactoring you can create a new category based on the members of the current class.
The refactoring is available for Objective-C only.
Perform the Extract Category refactoring
Select the desired class in the editor.
Select from the main or context menu.
In the dialog that opens, type the name of the new category, select the members that you want to move there, and click Extract.
Code example
| Before | After |
|---|---|
// Cat.h
@interface Cat : NSObject
- (void)purr;
- (void)meow;
@end
// Cat.m
@implementation Cat {
}
// This method will be extracted
// to a category
- (void)purr {
NSLog(@"Purr, purr, purr...");
}
- (void)meow {
NSLog(@"Meow!");
}
@end
|
// New category
// Cat+Purr.h
@interface Cat (Purr)
- (void)purr;
@end
// Cat+Purr.m
@implementation Cat (Purr)
- (void)purr {
NSLog(@"Purr, purr, purr...");
}
@end
// Cat.h
@interface Cat : NSObject
- (void)meow;
@end
// Cat.m
@implementation Cat {
}
- (void)meow {
NSLog(@"Meow!");
}
@end
|