objective-c - "unrecognized selector sent to instance"具有继承自 NSAttributedString 的类

Question

我有一个继承自 NSAttributedString 的类，如下所示:

文本.h:

#import <Foundation/Foundation.h>

@interface Text : NSAttributedString

-(id) initWithString:(NSString*) text andFont:(NSFont*)font andLineHeight:(float) lineHeight andLetterSpacing:(float) letterSpacing;

@end

文本.m:

#import "Text.h"

#import <Cocoa/Cocoa.h>

@implementation Text

-(id) initWithString:(NSString*) text andFont:(NSFont*)font andLineHeight:(float) lineHeight andLetterSpacing:(float) letterSpacing
{
    NSMutableParagraphStyle* paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    [paragraphStyle setParagraphStyle: [NSParagraphStyle defaultParagraphStyle]];
    paragraphStyle.lineHeightMultiple = lineHeight;
    NSDictionary* attributes =
    @{
        NSFontAttributeName: font,
        NSKernAttributeName: @(letterSpacing),
        NSParagraphStyleAttributeName: paragraphStyle
    };
    self = [super initWithString:text attributes:attributes];
    return self;
}

@end

当我像这样实例化该类时:

[[Text alloc] initWithString:@"Test" andFont:welcomeLabelFont andLineHeight:52 andLetterSpacing:0.0f]];

我收到以下异常:

2017-07-17 17:21:15.771610+0300 Test[41403:10128169] -[Text initWithString:attributes:]: unrecognized selector sent to instance 0x600000000f70

选择器在基类中可用，事件 ctrl 单击它会跳转到 NSAttributedText 类。谁能指出我做错了什么吗？参数不是零指针，并且调用似乎是合法的。唯一看起来奇怪的是错误的类名是 Text 而不是 NSAttributedString。

Answer 1

使用扩展来代替子类。像这样

// in NSAttributedString+init.h
//
@interface NSAttributedString (Init)

-(instancetype) initWithString:(NSString*) text andFont:(NSFont*)font andLineHeight:(float) lineHeight andLetterSpacing:(float) letterSpacing;

@end

然后，`

// in NSAttributedString+init.m
//
#import "NSAttributedString+init.h"

@implementation NSAttributedString (Init)

-(instancetype) initWithString:(NSString*) text andFont:(NSFont*)font andLineHeight:(float) lineHeight andLetterSpacing:(float) letterSpacing {
    // ...
}

在您想要使用便捷初始化程序的任何地方导入该扩展 header 。