Printing from NSMutableArray

Question

所以我想在NSMutableArray中打印用户。但字符串一直显示为零。

这是我的

int users = 0;
- (IBAction)addNewUser:(id)sender {
    NSString *string;
    string = userNameTextField.text;
    [usernameArray insertObject:string atIndex:users];
    users++;
    [self showUsers];
}
-(void)showUsers{
    for (int i = 0; i < users; i++){
        NSString *s = textView.text;
        NSString *add;
        add = [NSString stringWithFormat:@"%@ ",[usernameArray objectAtIndex:i]];
        NSString *display = [NSString stringWithFormat:@"%@ n %@", s, add];
        textView.text = display;
    }
}

我也试过

-(void)showUsers{
    for (int i = 1; i < users; i++){
        NSString *s = textView.text;
        NSString *add;
        add = [usernameArray objectAtIndex:i];
        NSString *display = [NSString stringWithFormat:@"%@ n %@", s, add];
        textView.text = display;
    }
}

Answer 1

首先尝试为对象使用更全面的名称。我正在重写你的代码。问题的常见原因：数组未初始化，启动for循环时int i等于1，因此在可变数组中缺少索引0处的对象。请尝试以下代码。

@interface InterfaceName : InterfaceInherits <IfDelegate> {
int usersCount;
NSMutableArray * usernameArray;
}
@implementation InterfaceName 
/*There's no more confident way to initialize a variable than in the init method of the class. */
-(id)init{
usersCount = 0;
//You have to be sure that your array is not nil
usernameArray = [NSMutableArray alloc]init]];
return self; 
}
- (IBAction)addNewUser:(id)sender {
NSString *username = [usernameTextField text];
[usernameArray insertObject:username atIndex:usersCount];
usersCount++;
//I'll omit the display as I'm not sure what you were doing with it. 
}
-(void)showUsers{
for (int i = 0; i < usersCount; i++){
    NSString *retrievedUser = [usernameArray objectAtIndex:i];
    NSString *display = [NSString stringWithFormat:@"User Retrieved : %@",retrievedUser];
    textView.text = display;
}
}

    @end