viewController.h文件:   #import <UIKit/UIKit.h> #import <Foundation/Foundation.h> @interface ViewController : UIViewController   {     //建立文本框     IBOutlet UITextField *textField;     //建立標簽顯示文字     IBOutlet UILabel *label;     } @property(nonatomic, retain) UITextField *textField; @property(nonatomic, retain) UILabel *label; -(IBAction)Click:(id)sender; @end   ViewController.m文件:   #import "ViewController.h" @implementation ViewController @synthesize textField, label;   - (void)viewDidLoad {     [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.     // 把已經讀取的Label標簽的文字替換成為本程序的顯示內容     label.text = @"請輸入文字";     }   -(IBAction)Click:(id)sender {     int textCount = textField.text.length;     //當長度大於30     if (textCount > 30) {         //輸出結果         label.text = @"Invalid Inputs";         //輸入文字清空         textField.text = NULL;     }     // 如果長度不大於30     else {         //輸出結果         NSString *result = [NSString stringWithFormat:@"輸入長度為：%d", textCount];         label.text = result;         //清空文字         textField.text = NULL;     } } - (void)viewDidUnload {     [super viewDidUnload];     // Release any retained subviews of the main view. }   -(void) didReceiveMemoryWarning  {     [super didReceiveMemoryWarning]; }   //釋放程序使用過的標簽 -(void) dealloc {     [label release];     [textField release];     //執行內存清理     [super dealloc]; } @end