不兼容的指针类型分配给'id< AVAudioPlayerDelegate>'来自'班级' [英] Incompatible pointer types assigning to 'id<AVAudioPlayerDelegate>' from 'Class'

问题描述

我有一个实用程序类来实现 AVAudioPlayerDelegate 协议。

I have a "Utility" class that implements the AVAudioPlayerDelegate protocol.

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：

My iOS application works well, however after migrating to iOS5 and XCode 4.2 the compiler started throwing this warning, located at the audioPlayer.delegate = self; line:

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

我怎么能摆脱它？

推荐答案

您已将方法声明为类方法，并且您尝试使用Class对象作为委托。但您无法向Class对象添加协议。

You've declared your method as a class method, and you're trying to use the Class object as the delegate. But you can't add protocols to Class objects.

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

You need to change playAudioFromFileName:... to an instance method and create an instance of Utility to use as the delegate. Maybe you want to have a single instance of Utility shared by all callers. This is the Singleton pattern, and it's pretty common in Cocoa. You do something like this:

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

Utility.m

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

Usage

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

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