ios - Tableview显示警报错误

Question

我正在编写一个简单的 tableview 应用程序，当点击该行时，会出现一个警告。

(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    NSString *rowValue =self.greekLetters[indexPath.row];
   // NSString *message=[[NSString alloc] initWithFormat:@"You selected%@!",rowValue];

   if (indexPath.row==0) {
        NSString *message=[[NSString alloc] initWithFormat:@"This is course aaaaa",rowValue];
    }

    if (indexPath.row==1) {
        NSString *message=[[NSString alloc] initWithFormat:@"This is course aaaaa"];
    }


    UIAlertView *alert=[[UIAlertView alloc] initWithTitle:@"Course introduction" message:message delegate:nil cancelButtonTitle:@"Return to courses list" otherButtonTitles:nil, nil];

    [alert show];
    [tableView deselectRowAtIndexPath:indexPath animated:YES];

但是，Xcode 不喜欢我这里的 if 语句，而下面的语句有效。

NSString *message=[[NSString alloc] initWithFormat:@"You selected%@!",rowValue];

谁能给我一个如何使用这里消息的例子吗？

Answer 1

这是作用域的问题。您需要在 if 语句之前声明消息:

NSString *message;

if (indexPath.row==0) {
    message=[[NSString alloc] initWithFormat:@"This is course aaaaa",rowValue];
}

else if (indexPath.row==1) {
    message=[[NSString alloc] initWithFormat:@"This is course aaaaa"];
}

UIAlertView *alert=[[UIAlertView alloc] initWithTitle:@"Course introduction" message:message delegate:nil cancelButtonTitle:@"Return to courses list" otherButtonTitles:nil];

[alert show];
[tableView deselectRowAtIndexPath:indexPath animated:YES];

但是，如果类(class)编号由行号确定:

NSString *rowValue =self.greekLetters[indexPath.row];

NSString *message = [[NSString alloc] initWithFormat:@"This is course %@",rowValue];

UIAlertView *alert=[[UIAlertView alloc] initWithTitle:@"Course introduction" message:message delegate:nil cancelButtonTitle:@"Return to courses list" otherButtonTitles:nil];

[alert show];
[tableView deselectRowAtIndexPath:indexPath animated:YES];