Question

在下面的代码中，我定义了一个创建箭头（作为图像）的函数，并将这些箭头添加到视图中。但是，我收到了Undeclared selector 'method'的警告。有人可以建议另一种方法来避免这种警告

-(void)createArrow:(NSString*)direction View:(UIView*)view
{
    int x,y;
    NSString *img;
    NSString *method;

    if ([direction isEqualToString:@"up"]){
        x = 55;
        y = 6;
        _arrow = _arrowUp;
        method = @"upTap";
        img = @"up-arrow.png";
    }else if ([direction isEqualToString:@"down"]){
        x = 55;
        y = 70;
        _arrow = _arrowDown;
        method = @"downTap";
        img = @"down-arrow.png";
    }else if ([direction isEqualToString:@"left"]){
        x = 22;
        y = 39;
        _arrow = _arrowLeft;
        method = @"leftTap";
        img = @"left-arrow.png";
    }else if ([direction isEqualToString:@"right"]){
        x = 90;
        y = 39;
        _arrow = _arrowRight;
        method = @"rightTap";
        img = @"right-arrow.png";
    }

    _arrow = [[UIImageView alloc] initWithFrame: CGRectMake(x, y, 27, 27)];
    [_arrow setImage:[UIImage imageNamed:img]];
    UITapGestureRecognizer *gest = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(method)];
    [_arrow setUserInteractionEnabled:YES];
    [_arrow addGestureRecognizer:gest];
    [view addSubview:_arrow];
}

Answer 1

选择器名称以C字符串形式给出，而不是NSStrings。将method更改为char *并删除前导@，或使用NSSelectorFromString(method)。

另一种选择是将method声明为SEL类型，并将其直接分配到if语句的每个块中。

Answer 2

Avi是对的。但更简单的是，为什么不只要method类型为SEL，并且在每种情况下，将其直接设置为要触发的选择器，然后将选择器传递给手势识别器？例如：

int x,y;
NSString *img;
SEL method;

if ([direction isEqualToString:@"up"]){
    ...
    method = @selector(upTap);
    ...
} else if ([direction isEqualToString:@"down"]){
    ...
    method = @selector(downTap);
    ...
} else if ([direction isEqualToString:@"left"]){
    ...
    method = @selector(leftTap);
    ...
} else if ([direction isEqualToString:@"right"]){
    ...
    method = @selector(rightTap);
    ...
}

...
UITapGestureRecognizer *gest = [[UITapGestureRecognizer alloc] initWithTarget:self action:method];
...

将String参数传递给UITapGestureRecognizer操作

2 个答案: