Objective-C中的构造函数

我正在尝试下面的示例程序

我不是在类B中调用+（void）initialise和-（id）init方法，而是自动调用它

是否-（void）初始值等于目标C中的默认构造函数

[super init]是否指向NSObject

如果我没有使用-（id）init方法，我会收到一条警告，说明该类的实现不完整

A.h级

#import <Foundation/Foundation.h>

static int ab;

@interface ClassA : NSObject {
    int a;
}

+ (void) initialize;
- (id) init;
- (void) displayNumOfInstance;
- (void) disp;

@end

B.h类

#import <Foundation/Foundation.h>
#import "ClassA.h"

@interface ClassB : ClassA {

}

- (void) display;

@end

类别2.m

#import <Foundation/Foundation.h>
#import "ClassA.h"

int main (int argc, const char * argv[]) {
    ClassA *a = [[ClassA alloc]init];
    [a disp];
    [a release];

    ClassB *b = [[ClassB alloc]init];
    [b display];
    [b release];

    ClassA *a1 = [[ClassA alloc]init];
    [a1 disp];
    [a1 release];

    ClassB *b1 = [[ClassB alloc]init];
    [b1 display];
    [b1 release];

    return 0;
}

---

默认构造通常以以下格式开始，即

-init

或其任何变体，例如

-initWithFrame:

方法

+initialize

是一种类方法（静态方法），在应用程序启动时至少调用一次。您可以使用此方法初始化对类的所有实例都有用的静态变量。此方法可能有助于初始化类的共享缓存或共享查找映射

对于

NSObject

，

-init

方法是指定的初始值设定项，但对于其他类，这可能有所不同。Apple使用

NS\u designed\u initializer

宏在其类标题中记录指定的初始值设定项。例如，

UIView

子类应该替代

-initWithFrame:

和

-initWithCoder:

，因为这些方法被标记为指定的初始值设定项

当子类化和实现自定义指定的初始值设定项时，不要忘记初始化超类。例如，让我们有一个

UIView

子类，它有一个自定义指定的初始值设定项

-initWithFrame:title:

。我们将按以下方式实施：

// A custom designated initializer for an UIView subclass. 
- (id)initWithFrame:(CGRect)frame title:(NSString *)title 
{
    // Initialize the superclass first. 
    //
    // Make sure initialization was successful by making sure 
    // an instance was returned. If initialization fails, e.g. 
    // because we run out of memory, the returned value would
    // be nil.
    self = [super initWithFrame:frame];
    if (self) 
    {
        // Superclass successfully initialized.
        self.titleLabel.text = title
    }
    return self;
}

// Override the designated initializer from the superclass to 
// make sure the new designated initializer from this class is 
// used instead.
- (id)initWithFrame:(CGRect)frame
{
    return [[self alloc] initWithFrame:frame title:@"Untitled"];
}

---

有关初始化的更多详细信息，请访问Apple开发者网站：

#import <Foundation/Foundation.h>
#import "ClassA.h"

int main (int argc, const char * argv[]) {
    ClassA *a = [[ClassA alloc]init];
    [a disp];
    [a release];

    ClassB *b = [[ClassB alloc]init];
    [b display];
    [b release];

    ClassA *a1 = [[ClassA alloc]init];
    [a1 disp];
    [a1 release];

    ClassB *b1 = [[ClassB alloc]init];
    [b1 display];
    [b1 release];

    return 0;
}

// A custom designated initializer for an UIView subclass. 
- (id)initWithFrame:(CGRect)frame title:(NSString *)title 
{
    // Initialize the superclass first. 
    //
    // Make sure initialization was successful by making sure 
    // an instance was returned. If initialization fails, e.g. 
    // because we run out of memory, the returned value would
    // be nil.
    self = [super initWithFrame:frame];
    if (self) 
    {
        // Superclass successfully initialized.
        self.titleLabel.text = title
    }
    return self;
}

// Override the designated initializer from the superclass to 
// make sure the new designated initializer from this class is 
// used instead.
- (id)initWithFrame:(CGRect)frame
{
    return [[self alloc] initWithFrame:frame title:@"Untitled"];
}