ios - 从其他类传递和获取数据时显示 null

Question

有两个类 DropDownPicker 和 editAddVehicle 类。只需在 editAddVehicle 中声明一个名为“brandID1”的字符串变量，我希望它从 DropDownPicker 类中获取数据。

这是我的代码:

DropDownPicker.h

@property(nonatomic,retain) NSArray *selectedIndex; 

DropDownPicker.m

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{

   if ([[dataArrayForPicker objectAtIndex:row] isKindOfClass:[NSString class]]){
      NSLog(@"Selected %@. Index is: %i brand id %@" , [dataArrayForPicker objectAtIndex:row], row,_selectedIndex[row]);
      editAddVehicle *controller=[[editAddVehicle alloc]init];
      controller.brandID1=_selectedIndex[row];
      NSLog(@"Brand Id %@",controller.brandID1);
      // Brand Id 50
      self->pickerTextFeild.text = [dataArrayForPicker objectAtIndex:row];
   }
   else 
      self->pickerTextFeild.text = [dataArrayForPicker objectAtIndex:row];
}

从 DropDownPicker 通过这行 controller.brandID1=_selectedIndex[row]; 代码轻松地我已将字符串存储在 crandID1 中，但为什么它editAddVehicle.m 处仍显示 null？

EditAddVehicle.h

@interface editAddVehicle : UIViewController
@property(nonatomic,retain)NSString *brandID1;
@end

EditAddVehicle.m

@interface editAddVehicle()<UITextFieldDelegate>
{
    NSString *brandID1;  
}
@end

@implementation editAddVehicle
@synthesize brandID1;
{
    UITextField *textFeild1=(UITextField *)[self.view viewWithTag:10];
    brand= [[DropDownPicker alloc]initWithTextFeild:textFeild1 withData:brandArray];
    [brand setPlaceHolder:@"Brand"];
    brand.selectedIndex=brandCode;
    [brand addTarget:self action:@selector(brandSelected:) forControlEvents:UIControlEventValueChanged];
}

-(void)brandSelected:(DropDownPicker *)sender{
    NSLog(@"%@",brandID1);
    // (null) why ?
}

Answer 1

这种错误的数据传递方式需要用户委托(delegate)或 NSNotificationCenter 传递数据。

这里是我的 NSNotificationCenter 示例

//在 DropDownPicker 中

   - (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
    {
    if ([[dataArrayForPicker objectAtIndex:row] isKindOfClass:[NSString class]]){
       NSLog(@"Selected %@. Index is: %i brand id %@" , [dataArrayForPicker objectAtIndex:row], row,_selectedIndex[row]);
       [[NSNotificationCenter defaultCenter]postNotificationName:@"NotificationForData" object:_selectedIndex[row]];

    }
        else{ 
self->pickerTextFeild.text = [dataArrayForPicker objectAtIndex:row];
// un comment if you want pass data here
// [[NSNotificationCenter defaultCenter]postNotificationName:@"NotificationForData" object:_selectedIndex[row]];
        }

}

在 editAddVehicle 中 //在viewdidload中

 [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(brandSelected:) name:@"NotificationForData" object:nil];

-(void)brandSelected:(NSNotification*)noti{
    NSString *brandID1 = [noti object];
    NSLog(@"%@",brandID1);
}