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@implementation ThisObject

-(void)start {

       SomeOtherObject *someOtherObject = [SomeOtherObject alloc];

       [someOtherObject doSomethingAndCallThisFunctionWhenUrDone:myCallBackFunction :self];

}

-(void)myCallBackFunction {

       // :)

}

基本上,我怎样才能做到这一点？

-(void)myFunction {

        unichar myBuffer[5];
        NSRange range = {0, 3};
        NSString *string = [NSString alloc];
        string = @"123";
        [string getCharacters:myBuffer :range];
}

得到警告

!NSString可能无法响应'-getCharacters ::'

然后在运行时执行SIGABRT.为什么？？？？？或者更好,我怎样才能让它发挥作用？