Question

当用户有按下登录按钮时，我想在用户输入用户名和密码时在警报视图中显示特定的名字。请帮我。提前致谢。将不胜感激。

    - (IBAction)LoginPressed:(id)sender
    { 


     if (managedObjContext == nil) {

    AppDelegate *app = (AppDelegate*)[UIApplication sharedApplication].delegate;


    managedObjContext= app.managedObjectContext;
}

NSFetchRequest *request =[[NSFetchRequest alloc]init];

NSEntityDescription *rocordTableEntity = [NSEntityDescription entityForName:@"RecordTable" inManagedObjectContext:managedObjContext];


NSPredicate *predicate = [NSPredicate predicateWithFormat:@"username==% @AND password==%@",L_usernameField.text,L_passwordField.text];

NSPredicate *pred = [NSPredicate predicateWithFormat:@"firstname=%@",[managedObjContext valueForKey:@"firstname"]];

[request setEntity:rocordTableEntity];
[request setPredicate:predicate];
[request setPredicate:pred];

NSError *error;

NSArray *arrarforCheckingUserANDPass = [managedObjContext executeFetchRequest:request       error:&error];
NSString *value =  [arrarforCheckingUserANDPass valueForKey:@"firstname"];



if (arrarforCheckingUserANDPass.count != 0) {




    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Welcome" message:value d elegate:nil cancelButtonTitle:@"Ok" otherButtonTitles: nil];

    [alert show];

}
else{

    NSLog(@"not matched");
}



}

Answer 1

你的第二个setPredicate会覆盖第一个firstName。你不需要它。您获得整个实体，然后只需访问NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"RecordTable"]; request.predicate = [NSPredicate predicateWithFormat: @"username==%@ AND password==%@",L_usernameField.text,L_passwordField.text]; NSArray *result = [self.managedObjectContext executeFetchRequest:request error:nil]; RecordTable *user = result.firstObject; if (user) { NSLog(@"The first name is %@.", user.firstName); }属性。你的第一个谓词语法错误。

{{1}}

顺便说一下，为什么你的方法以大写字母开头？这是一个非常糟糕的习惯。您的实体名称也是一场灾难。 “RecordTable”是您可以选择的最糟糕的实体名称。如果是用户，请将其命名为“用户”。遵循惯例，我也使用了firstName属性。

如何选择核心数据中的特定列？

1 个答案: