Question

我是iphone开发和Xcode的新手。而且我很难运行一个简单的演示应用程序，用于将我的文本域文本从一个视图传递到另一个视图中的标签编程.... 而且我不知道我哪里出错了[甚至NSLOG检查字符串来了......它说Null :(]

看看你们是否可以帮我找到我缺少代码的地方？提前谢谢！

这是我做的事情：

#import <UIKit/UIKit.h>


@interface ViewController : UIViewController<UITextFieldDelegate>{
    NSString *str;

}
@property(nonatomic,retain)NSString *str;

@end

ViewController.m *

#import "ViewController.h"
#import "nextViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize str;

- (void)viewDidLoad
{

    UITextField *txt =[[UITextField alloc]initWithFrame:CGRectMake(40, 40, 200, 30)];
    txt.borderStyle = UITextBorderStyleRoundedRect ;
    txt.delegate=self;
    [self.view addSubview:txt];


    UIButton *btn=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    btn.frame = CGRectMake(80, 80, 200, 30);
    [btn setTitle:@"Press" forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(btn:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];

    [super viewDidLoad];
}

- (BOOL)textFieldShouldEndEditing:(UITextField *)textField{
    self.str = [textField text];
    return YES;
}

-(IBAction)btn:(id)sender{



    nextViewController *next =[[nextViewController alloc]init];

[self.navigationController pushViewController:next animated:YES];

}

nextViewController.h *

#import <UIKit/UIKit.h>
#import "ViewController.h"

@interface nextViewController : UIViewController{
    NSString *str;
}
    @property(nonatomic,retain)NSString *str;

@end

nextViewController.m *

#import "nextViewController.h"
#import "ViewController.h"

@interface nextViewController ()

@end

@implementation nextViewController
@synthesize str;
- (void)viewDidLoad
{
    UILabel *lbl = [[UILabel alloc]init];
    lbl.frame=CGRectMake(40, 40, 200, 30);
    ViewController *VC =[[ViewController alloc]init];
    lbl.text=VC.str;`enter code here`

    [self.view addSubview:lbl];
    [super viewDidLoad];
}

Answer 1

您没有将nextViewController的{{1}}属性设置为您要将其设置为的字符串。

str

此外，您正在创建一个ViewController的新实例，没有明显的原因。只需使用以下命令将传递给nextViewController的字符串设置为标签：

-(IBAction)btn:(id)sender{
    nextViewController *next =[[nextViewController alloc]init];
    if (self.str)
        next.str = self.str;
    [self.navigationController pushViewController:next animated:YES];
}

Answer 2

你的错误就在这里

- (void)viewDidLoad
{
    UILabel *lbl = [[UILabel alloc]init];
    lbl.frame=CGRectMake(40, 40, 200, 30);
    ViewController *VC =[[ViewController alloc]init];
    lbl.text=VC.str;`enter code here`

    [self.view addSubview:lbl];
    [super viewDidLoad];
}

您正在创建ViewController的新实例（因此str中没有有效值）。

你应该在这里将str从viewcontroller设置为nextviewcontroller：

-(IBAction)btn:(id)sender{
    nextViewController *next =[[nextViewController alloc]init];
    next.str = [textField text];
    [self.navigationController pushViewController:next animated:YES];
}

并将viewdidlog从nextviewcontroller更改为

- (void)viewDidLoad
{
    UILabel *lbl = [[UILabel alloc]init];
    lbl.frame=CGRectMake(40, 40, 200, 30);
    lbl.text=self.str;
    [self.view addSubview:lbl];
    [super viewDidLoad];
}

Answer 3

尝试修改“btn”函数，如下所示：

-(IBAction)btn:(id)sender{
    nextViewController *next =[[nextViewController alloc]init];

    next.str = self.str; //<--- Add this.

    [self.navigationController pushViewController:next animated:YES];
}

Answer 4

我发现此链接对您有帮助

http://pragmaticstudio.com/blog/2013/2/5/unwind-segues

通过编程方式将Textfield值传递给另一个视图中的Label

4 个答案: