ios - 从按钮操作调用 AppDelegate 中的方法时出现错误。

Question

当我单击“保存”时，当它与 AppDelegate 对话时出现错误。

我确信，我在这里遗漏了一些小东西，但如果有人能快速给出答案，我将不胜感激。

这是我收到的错误:

-[AppDelegate saveNewUsername:username:]: unrecognized selector sent to instance 0x8e403d0

这是我的按钮操作:

-(IBAction)saveButtonPressed:(id)sender
{
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

NSString *userid = [appDelegate retrieveFromUserDefaults:@"userid"];
NSMutableArray *currentUser = [appDelegate getUserInfo:userid];
NSString *currentUsername = [currentUser objectAtIndex:0];

NSLog(@"%@", userid);

if ([currUsername.text isEqualToString:currentUsername]) {
    //here we'll check and make sure the new username is valid and doesn't already exist (for now just update local DB)
    if ([theNewUsername.text isEqualToString:@""]) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" message:@"You must enter something for your new username." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alert show];
    } else {
        int returnVal = [appDelegate saveNewUsername:userid username:theNewUsername.text];
        if (returnVal == 1) {
            [self dismissModalViewControllerAnimated:YES];
        } else {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"There was an error saving to the database." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
            [alert show];
        }
    }
} else {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"" message:@"The username you entered is not your current username." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
    [alert show];
}
}

这是我的 AppDelegate 方法:

-(int)saveNewUsername:(NSString *)user_id username:(NSString *)username
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0]; 
NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"somedbname.sqlite3"];

FMDatabase *db = [FMDatabase databaseWithPath:writableDBPath];

if (![db open]) {
    NSLog(@"Could not open db.");
    return 0;
} else {
    [db intForQuery:@"UPDATE user SET username=? WHERE user_id=?", username, user_id];

    if ([db hadError]) {
        NSLog(@"Error %d: %@", [db lastErrorCode], [db lastErrorMessage]);
        return 0;
    } else {
        return 1;
    }
}
}

Answer 1

您的代码看起来不错。所以我猜appDelegate实际上不是AppDelegate的实例。

AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

在那里设置一个断点并在调试器中查看它是否确实是 AppDelegate 的实例。