同样的需求，做Android客户端时在没有文本框时也可以通过inputMethodManager.toggleSoftInput(0, InputMethodManager.HIDE_NOT_ALWAYS);调出系统键盘。
但是，IOS中貌似没有这样的接口，所以可以采用“隐藏文本框”的方式，调出系统键盘，具体实现如下：
1、在ViewController.xib上放置一个ImageView和一个UITextField（代码中将其设置为隐藏），如下：

2、ViewController.h如下：

//  ViewController.h  
//  showKeyBoard  
//  
//  Created by Zhang Yanguang on 12-11-27.  
//  Copyright (c) 2012年 MyCompanyName. All rights reserved.  
//  
  
#import   
  
@interface ViewController : UIViewController{  
    BOOL hasOpenKeyBoard;//是否打开键盘  
}  
  
@property(strong,nonatomic)IBOutlet UIImageView *imgView;  
@property(strong,nonatomic)IBOutlet UITextField *textField;  
  
-(IBAction)showKeyBoard:(id)sender;  
@end  

3、ViewController.m如下：

//  ViewController.m  
//  showKeyBoard  
//  
//  Created by Zhang Yanguang on 12-11-27.  
//  Copyright (c) 2012年 MyCompanyName. All rights reserved.  
//  
  
#import "ViewController.h"  
  
@interface ViewController ()  
  
@end  
  
@implementation ViewController  
@synthesize imgView;  
@synthesize textField;  
- (void)viewDidLoad  
{  
    [super viewDidLoad];  
    // Do any additional setup after loading the view, typically from a nib.  
    //隐藏文本框  
    textField.hidden = YES;  
    //设置代理  
    textField.delegate = self;  
    hasOpenKeyBoard = false;  
}  
  
- (void)viewDidUnload  
{  
    [super viewDidUnload];  
    // Release any retained subviews of the main view.  
}  
  
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation  
{  
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);  
}  
  
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{  
    NSLog(@"touchesBegan...");  
    //[imgView becomeFirstResponder];  
    if(!hasOpenKeyBoard){  
        [textField becomeFirstResponder];  
    }else{  
        [textField resignFirstResponder];  
    }  
    hasOpenKeyBoard=!hasOpenKeyBoard;  
}  
  
#pragma mark UITextFieldDelegate Methods  
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{  
    NSLog(@"string=%@",string);  
    return YES;  
}  
  
@end  

方法shouldChangeCharactersInRange中可以监听到键盘输入。
4、效果如下：

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