objective-c - objective C 使用字符串调用方法

Question

嗨，我是 Objective-C 的新手，想知道是否有人可以帮助我解决这个问题。我有几个不同的方法，每个方法都需要 3 个输入值，通常使用

[self methodA:1 height:10 speed:3]

但是我想从 plist 中的字符串中读取方法名称所以例如如果字符串是 methodB 我会得到

[self methodB:1 height:10 speed:3] 

对于“方法C”

[self methodC:1 height:10 speed:3]

等等。

关于如何执行此操作的任何想法，我尝试使用 NSSelectorFromString 将字符串定义为选择器

NSString *string = [plistA objectForKey:@"method"];
SEL select = NSSelectorFromString(string);
[self performSelector:select:c height:b speed:a]; 

但是这不起作用，我们将不胜感激任何帮助。已经尝试了下面的解决方案但无法在这里工作是我尝试过的。

所以为了回顾一下，我有一些方法，例如

 spawnEnemyA:2 withHeight:3 withSpeed:4  
 spawnEnemyB:3 withHeight:2 withSpeed:5 

我想从 plist 文件中读取要传递给这些方法的值以及方法类型。我的代码如下，///////////////////////////////////////////////////////////

//这些是我从 plist 中读取的值，我希望我的方法使用这些值

    int a = [[enemySettings objectForKey:@"speed"] intValue];
    int b = [[enemySettings objectForKey:@"position"] intValue];
    int c = [[enemySettings objectForKey:@"delay"] intValue];

   // I Also read the method name from the plist and combine it into a single string  
    NSString *method = [enemySettings objectForKey:@"enemytype"];
    NSString *label1 = @"spawn";
    NSString *label2 = @":withHeight:withSpeed:";
    NSString *combined = [NSString stringWithFormat:@"%@%@%@",label1, method,label2];


    //Check that the string is correct get spawnEnemyA:withHeight:withSpeed:
    CCLOG(@"%@",combined);


//This is the Invocation part 
    NSInvocation * invocation = [ NSInvocation new ];

    [ invocation setSelector: NSSelectorFromString(combined)];
    [ invocation setArgument: &c atIndex: 2 ];
    [ invocation setArgument: &b atIndex: 3 ];
    [ invocation setArgument: &a atIndex: 4 ];

    [ invocation invokeWithTarget:self ];

    [invocation release ];

/////////////////////////////////////////////////////////////////

代码编译没有任何错误，但没有调用方法。有任何想法吗？干杯

Answer 1

您不能将 performSelector 用于具有 3 个(或更多)参数的方法。
但为了您的信息，这里是如何使用它:

SEL m1;
SEL m2;
SEL m3;

m1 = NSSelectorFromString( @"someMethodWithoutArg" );
m2 = NSSelectorFromString( @"someMethodWithAnArg:" );
m1 = NSSelectorFromString( @"someMethodWithAnArg:andAnotherOne:" );

[ someObject performSelector: m1 ];
[ someObject performSelector: m2 withObject: anArg ];
[ someObject performSelector: m2 withObject: anArg withObject: anOtherArg ];

对于超过 2 个参数的方法，您必须使用 NSInvocation类。
查看文档以了解如何使用它。

基本上:

NSInvocation * invocation = [ NSInvocation new ];

[ invocation setSelector: NSStringFromSelector( @"methodWithArg1:arg2:arg3:" ) ];

// Argument 1 is at index 2, as there is self and _cmd before
[ invocation setArgument: &arg1 atIndex: 2 ];
[ invocation setArgument: &arg2 atIndex: 3 ];
[ invocation setArgument: &arg3 atIndex: 4 ];

[ invocation invokeWithTarget: targetObject ];

// If you need to get the return value
[ invocation getReturnValue: &someVar ];

[ invocation release ];