NSInvocation invocationWithMethodSignature，方法签名参数不能为nil [英] NSInvocation invocationWithMethodSignature, method signature argument cannot be nil

问题描述

我遵循了cocos2d官方网站上的教程。我尝试在创建菜单时为菜单创建一些项目，但我会通过带有一个参数的选择器。对于每个项目，我都要通过不同的选择器。我认为这是问题所在，但我不明白为什么这是问题所在。我的头文件看起来是：

I followed tutorial from cocos2d official site . I try to create some items for a menu when creating them i pass a selector with one parameter. For each item i pass different selector . I think here is the problem , but i dont see realy why here is the problem. My header file looks :

// When you import this file, you import all the cocos2d classes
#import "cocos2d.h"
#import "CCTouchDispatcher.h"

// HelloWorldLayer
@interface HelloWorldLayer : CCLayer {

    CCSprite *first;
    CCSprite *second;
}

// returns a CCScene that contains the HelloWorldLayer as the only child
+(CCScene *) scene;
- (void) setUpMenus;
- (void) doSomethingOne: (CCMenuItem  *) menuItem;
- (void) doSomethingTwo: (CCMenuItem  *) menuItem;
- (void) doSomethingThree: (CCMenuItem  *) menuItem;

@end

执行文件：

// Import the interfaces
#import "HelloWorldLayer.h"

// HelloWorldLayer implementation
@implementation HelloWorldLayer

+(CCScene *) scene
{
    // 'scene' is an autorelease object.
    CCScene *scene = [CCScene node];

    // 'layer' is an autorelease object.
    HelloWorldLayer *layer = [HelloWorldLayer node];

    // add layer as a child to scene
    [scene addChild: layer];

    // return the scene
    return scene;
}

- (void) doSomethingOne: (CCMenuItem  *) menuItem 
{
    NSLog(@"The first menu was called");
}
- (void) doSomethingTwo: (CCMenuItem  *) menuItem 
{
    NSLog(@"The second menu was called");
}
- (void) doSomethingThree: (CCMenuItem  *) menuItem 
{
    NSLog(@"The third menu was called");
}


// on "init" you need to initialize your instance
-(id) init
{
    // always call "super" init
    // Apple recommends to re-assign "self" with the "super" return value
    if( (self=[super init])) {

        first = [CCSprite spriteWithFile:@"seeker.png"];
        first.position = ccp(100, 100);

        [self addChild:first];

        second = [CCSprite spriteWithFile:@"Icon.png"];
        second.position = ccp(50, 50);

        [self addChild:second];

        [self schedule:@selector(nextFrame:)];

        [self setUpMenus];

        self.isTouchEnabled = YES;
    }

    return self;
}


- (void) registerWithTouchDispatcher {

    [[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:YES];
}

- (BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {

    return YES;
}

- (void) ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event {

    CGPoint location = [self convertTouchToNodeSpace: touch];

    [second stopAllActions];

    [second runAction: [CCMoveTo actionWithDuration:1 position:location]];

}

- (void) nextFrame:(ccTime)dt {

    first.position = ccp( first.position.x + 100*dt, first.position.y );

    if (first.position.x > 480+32) {

        first.position = ccp( -32, first.position.y );
    }
}

- (void) setUpMenus {

    CCMenuItemImage *menuItem1 = [CCMenuItemImage itemFromNormalImage:@"myfirstbutton.png" 
                                                        selectedImage:@"myfirstbutton_selected.png" 
                                                               target:self 
                                                             selector:@selector(doSomenthingOne:)];

    CCMenuItemImage *menuItem2 = [CCMenuItemImage itemFromNormalImage:@"mysecondbutton.png" 
                                                        selectedImage:@"mysecondbutton_selected.png" 
                                                               target:self
                                                             selector:@selector(doSomenthingTwo:)];
    CCMenuItemImage *menuItem3 = [CCMenuItemImage itemFromNormalImage:@"mythirdbutton.png" 
                                                        selectedImage:@"mythirdbutton_selected.png" 
                                                               target:self selector:@selector(doSomenthingThree:)];

    CCMenu *myMenu = [CCMenu menuWithItems:menuItem1,menuItem2,menuItem3, nil];

    [myMenu alignItemsVertically];

    [self addChild:myMenu];

}



// on "dealloc" you need to release all your retained objects
- (void) dealloc
{
    // in case you have something to dealloc, do it in this method
    // in this particular example nothing needs to be released.
    // cocos2d will automatically release all the children (Label)

    // don't forget to call "super dealloc"
    [super dealloc];
}
@end

推荐答案

在所有三个菜单项创建调用中，您都有相同的错字。您告诉菜单项应该使用的选择器称为 doSomenthing ... （请注意中间是虚假的 n ）：

You've got the same typo in all three menu item creation calls. You're telling the menu items that the selector they should use is called doSomenthing... (note the spurious n in the middle):

CCMenuItemImage *menuItem1 = [...  selector:@selector(doSomenthingOne:)];
CCMenuItemImage *menuItem2 = [...  selector:@selector(doSomenthingTwo:)];
CCMenuItemImage *menuItem3 = [...  selector:@selector(doSomenthingThree:)];

但方法的实际名称为 doSomethingOne：， doSomethingTwo：和 doSomethingThree：。

but the actual names of your methods are doSomethingOne:, doSomethingTwo:, and doSomethingThree:.

错误消息的确切原因是，稍后，当菜单项需要执行该选择器时，它将要求您的类告诉它给您选择器的方法签名。由于您为商品指定了错误的选择器，因此您的班级不知道签名，并且它返回 nil 。该菜单项尝试以任何方式构造 NSInvocation 对象以执行其操作，此操作失败，因为无法使用 nil 签名。

The exact cause of the error message is that later, when the menu item needs to perform that selector, it will ask your class to tell it the method signature for the selector you gave it. Since you gave the item an incorrect selector, your class doesn't know the signature, and it returns nil. The menu item tries to construct an NSInvocation object anyways to perform its action, which fails because the invocation can't be created with a nil signature.

修正错别字，一切都会正常。

Fix the typos and everything should work fine.

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