当app进入前台时，如何在ViewController中更改标签

Question

我想在应用程序进入前台时更改视图控制器中的标签....：

SalaryAppV4AppDelegate.h

@interface SalaryAppV4AppDelegate：NSObject {

// --------------------------------------------- -

NSTimeInterval appEnteredBackground;

NSTimeInterval appEnteredForeground;

NSTimeInterval difference;

NSString *times;

// --------------------------------------------- -

SalaryAppV4AppDelegate.m

• （void）applicationWillEnterForeground：（UIApplication *）application

{

//perform -(IBAction)DoThis

FirstViewController* controller = [FirstViewController alloc];
[controller DoThis]; 




//releasing
[dateFormatter release];

}

// --------------------------------------------- ------------------------

FirstViewController.h

导入UIKit / UIKit.h＆gt; 导入“SalaryAppV4AppDelegate.h”

@interface FirstViewController：UIViewController {

IBOutlet UITextField *text1;
IBOutlet UILabel *label;
IBOutlet UILabel *labeltotal;
IBOutlet UILabel *differenceLabel;


int i;
float number1;
NSTimer *timer;

SalaryAppV4AppDelegate *appDelegate;

}

//操作

- （IBAction为）复位：（ID）发送者;

- （IBAction为）backgroundTouched：（ID）发送者;

- （IBAction）beginTimer;

- （void）DoThis;

//属性

@end

// --------------------------------------------- -----------------------

FirstViewController.m

- （IBAction）DoThis {

appDelegate = [[[UIApplication sharedApplication] delegate] retain];

//This Doesn't Work :(
label.text = @"IT Has Worked";


//This Works
NSLog(@"%@", appDelegate.times);

}

// --------------------------------------------- -----------

我只想将label.text ti更改为任何内容，但在viewcontroller更改中没有任何内容......