Using stringByAppendingString to add character to existing string in Xcode/objective-C

Question

I am trying to add the character "1" to the existing value of a textbox "output" in Xcode objective-C.

I am trying to use the "stringByAppendingString" function, and have looked at some examples and can't seem to get this to work.

Is my syntax just wrong?

- (IBAction)pressOne:(id)sender {
    NSString *str1 = output.text;

    output.text = [str1  stringByAppendingString:[@"1"];

}

Answer 1

摆脱@符号前的迷路括号：

output.text = [str1 stringByAppendingString:@"1"];

Answer 2

试试[str1 stringByAppendingString:@"1"];

Answer 3

删除括号：

output.text = [str1  stringByAppendingString:@"1"];