Question

我有一个定义的类别：

#import <Foundation/Foundation.h>

@interface NSString (MyApp)

+ (UIColor *)colorFromHexString;

@end


#import "NSString+MyApp.h"

@implementation NSString (MyApp)

+ (UIColor *)colorFromHexString
{
    self = [self stringByReplacingOccurrencesOfString:@"#" withString:@""];
    unsigned rgbValue = 0;
    NSScanner *scanner = [NSScanner scannerWithString:hexString];
    [scanner scanHexInt:&rgbValue];
    return [UIColor colorWithRed:((rgbValue & 0xFF0000) >> 16)/255.0 green:((rgbValue & 0xFF00) >> 8)/255.0 blue:(rgbValue & 0xFF)/255.0 alpha:1.0];
}

@end

我在行self = [self stringByReplacingOccurrencesOfString:@"#" withString:@""];上收到错误消息："No know class method for selector stringByReplacingOccurrencesOfString:withString" and "cannot assign self in a class method"。

我很困惑为什么我无法在NSString Category中执行此操作。我看到examples online与NSString Category中的'self'非常相似，所以我不确定它为什么不在这里工作。

任何人都知道我做错了什么？

Answer 1

您的代码中存在多个错误。

使用实例方法（ - ）代替静态方法（+）

var tag = document.createElement('script');
tag.src = "https://www.youtube.com/iframe_api";

var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);

var player;
function onYouTubeIframeAPIReady(){
    player = new YT.Player('MyVideoID',{
        events: {
            'onReady': onPlayerReady,
            'onStateChange': onPlayerStateChange
        }
    });
}

function onPlayerReady(event){
    event.target.playVideo();
}

function onPlayerStateChange(event) {
    if (event.data == YT.PlayerState.PLAYING) {
        var slideTimeMS = 10000; /* This is a variable which exists in my external file which I would like the player state to manipulate
    }
}

同样在第1行分配// INCORRECT. self in a static method points to class object // + (UIColor *)colorFromHexString // CORRECT. self is instance method points to instance of class. - (UIColor *)colorFromHexString而不是hexString。

self

NSString类别中没有Know Class方法

1 个答案: