blocks|key|2101748|text|您已经将方法声明为类方法，并且尝试使用class对象作为委托。但是不能向Class对象添加协议。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2101749|您需要将playAudioFromFileName:...更改为实例方法，并创建用作委托的Utility实例。也许您想让所有调用者共享一个Utility实例。这是单例模式，在可可中很常见。你做这样的事：|offset|length|style|CODE|2101750|Utility.h|2101751|@interface+Utility+:+NSObject+<AVAudioPlayerDelegate>
%2B+(Utility+*)sharedUtility;
@end|code-block|syntax|javascript|2101752|Utility.m|2101753|@implementation+Utility

%2B+(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|2101754|用法|2101755|[[Utility+sharedUtility]+playAudioFromFileName:@"quack"+ofType:"mp3"+withPlayerFinishCallback:@selector(doneQuacking:)+onObject:duck];|2101756|entityMap^0|0|4|P|19|7|1X|7|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@$D|10|E|11|F|G]|$D|12|E|13|F|G]|$D|14|E|15|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|16|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|17|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|19|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1A|8|@]|9|@]|A|$]]|$1|U|3|V|5|L|7|1B|8|@]|9|@]|A|$M|N]]|$1|W|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|X|$]]

<p>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.</p>

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

<h2>Utility.h</h2>

<pre><code>@interface Utility : NSObject &lt;AVAudioPlayerDelegate&gt;
+ (Utility *)sharedUtility;
@end
</code></pre>

<h2>Utility.m</h2>

<pre><code>@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
</code></pre>

<h2>Usage</h2>

<pre><code>[[Utility sharedUtility] playAudioFromFileName:@"quack" ofType:"mp3" withPlayerFinishCallback:@selector(doneQuacking:) onObject:duck];
</code></pre>


blocks|key|127150|text|当您不需要类的实例时，只需手动获得警告：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|127151|audioPlayer.delegate+=+(id<AVAudioPlayerDelegate>)self;|code-block|syntax|javascript|127152|另一方面，请注意，如果您需要一个委托，这意味着您应该有一个类的实例作为一种良好的编码实践，而不是静态类。它可以很容易地成为一个辛格尔顿：|offset|length|127153|static+id+_sharedInstance+=+nil;
%2B(instancetype)sharedInstance
{
++++static+dispatch_once_t+p;
++++dispatch_once(&p,+%5E{
++++++++_sharedInstance+=+[[self+alloc]+init];
++++});
++++return+_sharedInstance;
}|127154|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/legacy/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/CocoaObjects.html#//apple_ref/doc/uid/TP40002974-CH4-SW32^0|0|0|1R|4|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@$I|X|J|Y|1|Z]]|A|$]]|$1|K|3|L|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

<p>When you don't need an instance of a Class, just manually get ride of the warning:</p>

<pre><code>audioPlayer.delegate = (id&lt;AVAudioPlayerDelegate&gt;)self;
</code></pre>

<p>On the other hand, please note that if you need a Delegate, it means you should have an instance of a Class as a good coding practice instead of a static Class. It can be made a <a href="https://developer.apple.com/legacy/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/CocoaObjects.html#//apple_ref/doc/uid/TP40002974-CH4-SW32" rel="nofollow">singleton</a> easily:</p>

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


<p>I have a "<strong>Utility</strong>" class that implements the <strong>AVAudioPlayerDelegate</strong> protocol.</p>

<p>This is my <strong>Utility.h</strong></p>

<pre><code>@interface Utility : NSObject &lt;AVAudioPlayerDelegate&gt;
{
}
</code></pre>

<p>And this is its counterpart <strong>Utility.m</strong></p>

<pre><code>@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
    ...
}
</code></pre>

<p>My iOS application works well, however after migrating to iOS 5 and Xcode 4.2 the compiler started throwing this warning, located at the <code>audioPlayer.delegate = self;</code> line: </p>

<pre><code>Incompatible pointer types assigning to id &lt;AVAudioPlayerDelegate&gt; from 'Class'
</code></pre>

<p>How can I get rid of it?</p>


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

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个实现AVAudioPlayerDelegate协议的“实用程序”类。这是我的Utility.h@interface Utility : NSObject <AVAudioPlayerDelegate>{}这是对应的Utility.m@implementation Utilitystatic AVAudioPla...

问不兼容指针类型从“类”分配给“id<AVAudioPlayerDelegate>”
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问不兼容指针类型从“类”分配给“id<AVAudioPlayerDelegate>”EN