从“Class”分配给“id”的指针类型不兼容

我有一个 ”Utility“ 实现的类AVAudioPlayerDelegate协议。

这是我的实用程序.h

@interface Utility : NSObject <AVAudioPlayerDelegate>
{
}

这是它的对应物实用程序.m

@implementation Utility

static AVAudioPlayer *audioPlayer;

+ (void)playAudioFromFileName:(NSString *)name ofType:(NSString *)type withPlayerFinishCallback:(SEL)callback onObject:(id)callbackObject
{
    ... 
    audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL: [self getResourceURLForName:name ofType:type] error: nil];
    audioPlayer.delegate = self; // this is the line that causes the Warning
    ...
}

我的 iOS 应用程序运行良好，但是在迁移到 iOS 5 和 Xcode 4.2 后，编译器开始抛出此警告，位于audioPlayer.delegate = self; line:

Incompatible pointer types assigning to id <AVAudioPlayerDelegate> from 'Class'

我怎样才能摆脱它？

您已将方法声明为类方法，并且尝试使用 Class 对象作为委托。但是您不能将协议添加到 Class 对象。

你需要改变playAudioFromFileName:...到一个实例方法并创建一个实例Utility用作代表。也许您想要一个实例Utility由所有呼叫者共享。这就是 Singleton 模式，在 Cocoa 中很常见。你做这样的事情：

实用程序.h

@interface Utility : NSObject <AVAudioPlayerDelegate>
+ (Utility *)sharedUtility;
@end

实用程序.m

@implementation Utility

+ (Utility *)sharedUtility
{
    static Utility *theUtility;
    @synchronized(self) {
        if (!theUtility)
            theUtility = [[self alloc] init];
    }
    return theUtility;
}

- (void)playAudioFromFileName:(NSString *)name ofType:(NSString *)type withPlayerFinishCallback:(SEL)callback onObject:(id)callbackObject
{
    ... 
    audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL: [self getResourceURLForName:name ofType:type] error: nil];
    audioPlayer.delegate = self;
    ...
}

@end

Usage

[[Utility sharedUtility] playAudioFromFileName:@"quack" ofType:"mp3" withPlayerFinishCallback:@selector(doneQuacking:) onObject:duck];