UITextField 禁用复制粘贴功能

- (BOOL)canPerformAction:(SEL)action withSender:(id)sender
    {
        // 禁用粘贴功能
        if (action == @selector(paste:))
            return NO;
 
        // 禁用选择功能
        if (action == @selector(select:))   
            return NO;   
 
        // 禁用全选功能
        if (action == @selector(selectAll:))   
            return NO;
 
        return [super canPerformAction:action withSender:sender];