不兼容的指针类型分配给＆＃39; id <avaudioplayerdelegate>＆＃39;来自＆＃39; Class＆＃39; </avaudioplayerdelegate>

Question

我有一个“实用程序”类来实现 AVAudioPlayerDelegate 协议。

这是我的 Utility.h

@interface Utility : NSObject <AVAudioPlayerDelegate>
{
}

这是它的对应 Utility.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iOS5和XCode 4.2后，编译器开始抛出此警告，位于audioPlayer.delegate = self;行：

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

我怎么能摆脱它？

Answer 1

您已将方法声明为类方法，并且您尝试将Class对象用作委托。但是你无法向Class对象添加协议。

您需要将playAudioFromFileName:...更改为实例方法，并创建Utility的实例以用作委托。也许您希望所有呼叫者共享一个Utility实例。这是Singleton模式，在Cocoa中很常见。你做这样的事情：

Utility.h

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

Utility.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

用法

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

Answer 2

如果您不需要Class的实例，只需手动获取警告：

audioPlayer.delegate = (id<AVAudioPlayerDelegate>)self;

另一方面，请注意，如果您需要Delegate，则意味着您应该将Class的实例作为良好的编码实践而不是静态类。它可以很容易地成为singleton：

static id _sharedInstance = nil;
+(instancetype)sharedInstance
{
    static dispatch_once_t p;
    dispatch_once(&p, ^{
        _sharedInstance = [[self alloc] init];
    });
    return _sharedInstance;
}