and vice versa. It’s simple: when you serialize an object, you convert it from a Swift-only data format to a stream (or “series”) of bytes. Both properties are inferred to be of type Double by assigning a default value of 0.0. If the type conversion cannot maintain the value, the initializer fails. Before we can save and load data with NSKeyedArchiver, our Book class needs to adopt the NSCoding protocol. The example below defines a structure called Size with two properties called width and height. Designated initializers for classes are written in the same way as simple initializers for value types: Convenience initializers are written in the same style, but with the convenience modifier placed before the init keyword, separated by a space: To simplify the relationships between designated and convenience initializers, Swift applies the following three rules for delegation calls between initializers: These rules are illustrated in the figure below: Here, the superclass has a single designated initializer and two convenience initializers. These actions are described in the following sections. Write the required modifier before the definition of a class initializer to indicate that every subclass of the class must implement that initializer: You must also write the required modifier before every subclass implementation of a required initializer, to indicate that the initializer requirement applies to further subclasses in the chain. The type of the array is inferred to be [ShoppingListItem]. Each class is successfully initialized by calling its newly created convenience init method. The main difference is that during phase 1, Objective-C assigns zero or null values (such as 0 or nil) to every property. (id : Int?) In practice, this means that you do not need to write initializer overrides in many common scenarios, and can inherit your superclass initializers with minimal effort whenever it is safe to do so. The boardColors array is initialized with a closure to set up its color values: Whenever a new Chessboard instance is created, the closure is executed, and the default value of boardColors is calculated and returned. To represent this game board, the Chessboard structure has a single property called boardColors, which is an array of 64 Bool values. Following Apple's specs this 3 rules must be respected: A designated initializer must call a designated initializer from its immediate superclass. A class can have more than one designated initializer. These are optional and can be used for a custom setup. This base class declares a stored property called numberOfWheels, with a default Int value of 0. A designated initializer must call a designated initializer from its immediate superclass. When placed before the init keyword, the convenience keyword identifies a convenience initializer.. An initializer without the convenience keyword preceding is known as a designated initializer.. In the first phase, each stored property is assigned an initial value by the class that introduced it. ", "This is not a defined temperature unit, so initialization failed. A convenience initializer must call another initializer from the sameclass… convenience init:: Convenience-Initialisierer sind sekundär und unterstützen Initialisierer für eine Klasse. This designated initializer matches a designated initializer from the superclass of Bicycle, and so the Bicycle version of this initializer is marked with the override modifier. (name:) initializer with a nonfailable init(name:) initializer. First a recap on the two types of initializer: A designated initializer is the primary initializer for a class. The example below defines a structure called Chessboard, which models a board for the game of chess. Two-phase initialization prevents property values from being accessed before they are initialized, and prevents property values from being set to a different value by another initializer unexpectedly. The subclass in this figure has two designated initializers and one convenience initializer. You specify a default property value by assigning an initial value to the property when it is defined. In some cases, this requirement is satisfied by inheriting one or more designated initializers from a superclass, as described in Automatic Initializer Inheritance below. Question or problem with Swift language programming: I am having troubles to understand the difference between both, or the purpose of the convenience init. Swift’s two-phase initialization process is similar to initialization in Objective-C. Use this approach if you need to add a potential failure state to an existing initialization process that does not otherwise fail. It is automatically assigned a default value of nil, meaning “no string yet”, when a new instance of SurveyQuestion is initialized. It introduces an Int property called quantity (in addition to the name property it inherits from Food) and defines two initializers for creating RecipeIngredient instances: The figure below shows the initializer chain for the RecipeIngredient class: The RecipeIngredient class has a single designated initializer, init(name: String, quantity: Int), which can be used to populate all of the properties of a new RecipeIngredient instance. There are no further superclasses to initialize, and so no further delegation is needed. { guard let x = id else { return nil } self.init (id: x, desc: "Blah") } Unless there is a specific reason to do so, you can also avoid using a failable initializer in the first place. After the array is created, the name of the ShoppingListItem at the start of the array is changed from "[Unnamed]" to "Orange juice" and it is marked as having been purchased. swift - Was ist der Unterschied zwischen Convenience Init und Init in schnellen, expliziten Beispielen besser . You do not write the override modifier when overriding a required designated initializer: You do not have to provide an explicit implementation of a required initializer if you can satisfy the requirement with an inherited initializer. Adopting NSCoding in Swift. The memory for these stored properties is now initialized. The init() initializer provides a default placeholder name for a new food by delegating across to the Food class’s init(name: String) with a name value of [Unnamed]: The second class in the hierarchy is a subclass of Food called RecipeIngredient. A convenience initializer must ultimately call a designated initializer. Swift’s approach prevents a situation in which a simple initializer from a superclass is inherited by a more specialized subclass and is used to create a new instance of the subclass that is not fully or correctly initialized. To cope with initialization conditions that can fail, define one or more failable initializers as part of a class, structure, or enumeration definition. )", // basicRect's origin is (0.0, 0.0) and its size is (0.0, 0.0), // originRect's origin is (2.0, 2.0) and its size is (5.0, 5.0), // centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0), // Hoverboard: 0 wheel(s) in a beautiful silver, // Prints "12345.0 conversion to Int maintains value of 12345", conversion to Int does not maintain value", // Prints "3.14159 conversion to Int does not maintain value", // someCreature is of type Animal?, not Animal, "An animal was initialized with a species of, // Prints "An animal was initialized with a species of Giraffe", // anonymousCreature is of type Animal?, not Animal, "The anonymous creature could not be initialized", // Prints "The anonymous creature could not be initialized", "This is a defined temperature unit, so initialization succeeded. Strictly speaking, initializers do not return a value. However, initializers do not have an identifying function name before their parentheses in the way that functions and methods do. The example below defines a class called Document. For more information, see Automatic Initializer Inheritance below. This initializer is therefore inherited by RecipeIngredient. You also cannot use the implicit self property, or call any of the instance’s methods. You implement this initialization process by defining initializers, which are like special methods that can be called to create a new instance of a particular type. ). You write return nil within a failable initializer to indicate a point at which initialization failure can be triggered. Initializers prepare a class, struct or enum by setting stored properties before they are used. You write a failable initializer by placing a question mark after the init keyword (init?). The Food class introduces a single String property called name and provides two initializers for creating Food instances: The figure below shows the initializer chain for the Food class: Classes do not have a default memberwise initializer, and so the Food class provides a designated initializer that takes a single argument called name. A designated initializer must call a designated initializer from its immediate superclass. with init! However, it is not appropriate for an animal to have an empty string as the value of its species property. This convenience initializer assumes a quantity of 1 for any RecipeIngredient instance that is created without an explicit quantity. A designated initializer of a subclass cannot call a Convenience initfrom its superclass. Initialization parameters have the same capabilities and syntax as function and method parameters. This initializer starts by assigning the passed quantity argument to the quantity property, which is the only new property introduced by RecipeIngredient. initializer causes initialization to fail. You can write the Fahrenheit structure from above in a simpler form by providing a default value for its temperature property at the point that the property is declared: You can customize the initialization process with input parameters and optional property types, or by assigning constant properties during initialization, as described in the following sections. convenience init? How to solve the problem: Solution 1: Standard init: Designated initializers are the primary initializers for a class. You can provide initialization parameters as part of an initializer’s definition, to define the types and names of values that customize the initialization process. Although you write return nil to trigger an initialization failure, you do not use the return keyword to indicate initialization success. init (nm: nm, ad: ad)} Diese einfache Initialisierung auf Null könnte auch durch Setzen des Standardwerts der Eigenschaft auf Null erfolgen. If a stored property’s default value requires some customization or setup, you can use a closure or global function to provide a customized default value for that property. It illustrates how the designated initializers in this hierarchy act as “funnel” points for class initialization, simplifying the interrelationships among classes in the chain: Class initialization in Swift is a two-phase process. This process, known as initializer delegation, avoids duplicating code across multiple initializers. It cannot be modified by a subclass. If you want your custom value type to be initializable with the default initializer and memberwise initializer, and also with your own custom initializers, write your custom initializers in an extension rather than as part of the value type’s original implementation. For more information, see Extensions. Structure types automatically receive a memberwise initializer if they don’t define any of their own custom initializers. Otherwise they are exactly the same. In either case, if you delegate to another initializer that causes initialization to fail, the entire initialization process fails immediately, and no further initialization code is executed. What is the difference between convenience init vs init in swift, explicit examples better (4) . Swift defines two kinds of initializers for class types to help ensure all stored properties receive an initial value. You always write the override modifier when overriding a superclass designated initializer, even if your subclass’s implementation of the initializer is a convenience initializer. Once the top of the chain is reached, and the final class in the chain has ensured that all of its stored properties have a value, the instance’s memory is considered to be fully initialized, and phase 1 is complete. Here’s how phase 2 looks for the same initialization call: The superclass’s designated initializer now has an opportunity to customize the instance further (although it does not have to). If an empty string is found, an initialization failure is triggered. Likewise, the failable initializer for Product checks the name value, and the initializer process fails immediately if name is the empty string. Both initializers convert their single argument into the corresponding Celsius value and store this value in a property called temperatureInCelsius. The default value also makes it easier for you to take advantage of default initializers and initializer inheritance, as described later in this chapter. Classes, however, can inherit from other classes, as described in Inheritance. You do not have to provide convenience initializers if your class does not require them. ️ Subscribe News Apps Articles About 2019/08/25 Swift init patterns. This satisfies rules 2 and 3 from above. A class does not require convenience initializers. You can define a convenience initializer to call a designated initializer from the same class as the convenience initializer with some of the designated initializer’s parameters set to default values. A convenience initializer is a secondary initializer that must call a designated initializer of the same class. But a class has Inheritance, The main difference in their syntax, is that convenience initializers have the convenience keyword before the init.. Color provides an initializer with three appropriately named parameters of type Double for its red, green, and blue components. You can use forced unwrapping in an initializer to call a failable initializer from the superclass as part of the implementation of a subclass’s nonfailable initializer. CartItem introduces a stored constant property called quantity and ensures that this property always has a value of at least 1: The failable initializer for CartItem starts by validating that it has received a quantity value of 1 or more. This initializer simply assigns the origin and size argument values to the appropriate stored properties: The third Rect initializer, init(center:size:), is slightly more complex. You can omit either property or both properties, and the initializer uses the default value for anything you omit—for example: Initializers can call other initializers to perform part of an instance’s initialization. When you assign a default value to a stored property, or set its initial value within an initializer, the value of that property is set directly, without calling any property observers. Warum sollte Swift mich zwingen, convenience vor meinen Initialisierer zu stellen, nur weil ich self.init aufrufen self.init? The init() initializer for Bicycle starts by calling super.init(), which calls the default initializer for the Bicycle class’s superclass, Vehicle. Therefore, the question is.. What is the defference between (designated) init and convenience init? Instead of making an explicit call to super.init(), this initializer relies on an implicit call to its superclass’s initializer to complete the process. This protocol formalizes the way custom classes, like Book, can be serialized and deserialized.. What’s serialization anyway? Their primary role is to ensure that new instances of a type are correctly initialized before they are used for the first time. Calling this initializer returns a Rect instance whose origin and size properties are both initialized with the default values of Point(x: 0.0, y: 0.0) and Size(width: 0.0, height: 0.0) from their property definitions: The second Rect initializer, init(origin:size:), is functionally the same as the memberwise initializer that the structure would have received if it did not have its own custom initializers. The rules for how initializer delegation works, and for what forms of delegation are allowed, are different for value types and class types. A failable initializer is used to find an appropriate enumeration case for a Character value representing a temperature symbol: You can use this failable initializer to choose an appropriate enumeration case for the three possible states and to cause initialization to fail if the parameter does not match one of these states: Enumerations with raw values automatically receive a failable initializer, init? As soon as all properties of the superclass have an initial value, its memory is considered fully initialized, and phase 1 is complete. Note that if you define a custom initializer for a value type, you will no longer have access to the default initializer (or the memberwise initializer, if it is a structure) for that type. Subclasses can modify inherited variable properties during initialization, but can not modify inherited constant properties. Once the superclass’s designated initializer is finished, the subclass’s designated initializer can perform additional customization (although again, it does not have to). An initializer can also perform other required setup before the programmer deems it to be ready for use. Stored properties cannot be left in an indeterminate state. It then calls (or delegates) to the init(origin:size:) initializer, which stores the new origin and size values in the appropriate properties: The init(center:size:) initializer could have assigned the new values of origin and size to the appropriate properties itself. The example above uses the default initializer for the ShoppingListItem class to create a new instance of the class with initializer syntax, written as ShoppingListItem(), and assigns this new instance to a variable called item. They must call a designated initializer of the same class. The following example shows designated initializers, convenience initializers, and automatic initializer inheritance in action. One convenience initializer calls another convenience initializer, which in turn calls the single designated initializer. The following example defines a structure called Color, with three constant properties called red, green, and blue. However, it is more convenient (and clearer in intent) for the init(center:size:) initializer to take advantage of an existing initializer that already provides exactly that functionality. initialization convenience-methods (5) Ich habe Probleme, den Unterschied zwischen beiden zu verstehen, oder den Zweck des Convenience Init. Reading the documentation I found that these two rules apply to my question: In the code below I fall under the first rule and all my convenience initializers are inherited into ClassB. Both initializers can be used to create a new Color instance, by providing named values for each initializer parameter: Note that it is not possible to call these initializers without using argument labels. -- Chris McIntyre > On Jul 18, 2017, at 6:46 PM, Jens Persson via swift-users wrote: > > That is not true. The Food class does not have a superclass, and so the init(name: String) initializer does not need to call super.init() to complete its initialization. Properties of optional type are automatically initialized with a value of nil, indicating that the property is deliberately intended to have “no value yet” during initialization. The superclass’s designated initializer makes sure that all of the superclass properties have a value. The default initializer (when available) is always a designated initializer for a class, and can be used to create a new Vehicle instance with a numberOfWheels of 0: The next example defines a subclass of Vehicle called Bicycle: The Bicycle subclass defines a custom designated initializer, init(). Unlike subclasses in Objective-C, Swift subclasses do not inherit their superclass initializers by default. Following Apple's specs this 3 rules must be respected: Image source: The Swift Programming Language, This modified text is an extract of the original Stack Overflow Documentation created by following, Function as first class citizens in Swift, Getting Started with Protocol Oriented Programming, Customizing initialization with paramaters. As mentioned above, subclasses do not inherit their superclass initializers by default. Color also provides a second initializer with a single white parameter, which is used to provide the same value for all three color components. 注意事项： 增加init的初始化方法 ; 必须调用Swift同一个类中的designated初始化完成设置 ; convenience的初始化方法不能被子类重写或者是从子类中以super的方式被调用 Was it ever explained why the syntax is different label of fromKelvin and Size. Initializer ’ s stored properties—including any properties is found multiple ways of being initialized initialization. Not appropriate for an Animal to have only one this ensures that the constant! 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