完成這一功能的前提是，你應該先安裝好我上一節所說道的window-Based Application模版：

  教程地址：http://www.baiduhome.net/lib/view/open1341882507072.html

接著我們要新建一個window-Based Application 模版

我們創建一個名為HypnosisView的objetctive-C class文件：

HypnosisView.h:

#import <FOUNDATION foundation.h="">

@interface HypnosisView : UIView
{
}
@end</foundation></pre>




HypnosisView.m: 
在這個文件中我們加入了繪制了一個同心圓的圖形


#import "HypnosisView.h"

@implementation HypnosisView

(void)drawRect:(CGRect)rect
{
  // 獲取繪圖區域
  CGRect bounds = [self bounds];
// 計算中心點
  CGPoint center;
  center.x = bounds.origin.x + bounds.size.width / 2.0;
  center.y = bounds.origin.y + bounds.size.height / 2.0;
// 計算中心點至邊界角的距離
  float maxRadius = hypot(bounds.size.width, bounds.size.height) / 2.0;
// 獲取繪圖所需要的上下文
  CGContextRef context = UIGraphicsGetCurrentContext();
// 用10點的寬度來繪制所有的線條
  CGContextSetLineWidth(context, 10);
// 線條顏色設為淡灰
  [[UIColor lightGrayColor] setStroke];
// 繪制同心圓
  for (float currentRadius = maxRadius; currentRadius > 0; currentRadius -= 20)
  {

  CGContextAddArc(context, center.x, center.y, 
                  currentRadius, 0.0, M_PI * 2.0, YES);
  CGContextStrokePath(context);

}



NSString *text = @"hi: i am henrymorgen.";

// 獲取繪圖所需要的字體
UIFont *font = [UIFont boldSystemFontOfSize:28];

// 計算繪圖位置
CGRect textRect;
textRect.size = [text sizeWithFont:font];
textRect.origin.x = center.x - textRect.size.width / 2.0;
textRect.origin.y = center.y - textRect.size.height / 2.0;

// 將當前上下文的填充色設為黑色
[[UIColor blackColor] setFill];

[text drawInRect:textRect
        withFont:font];

}
@end</pre>



接著我們配置代理 AppDelegate.h: 


#import <UIKIT uikit.h="">

@class HypnosisView;
@interface HypnosisterAppDelegate : NSObject
    <UIAPPLICATIONDELEGATE, uiscrollviewdelegate=""> {

HypnosisView *view;

}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@end</UIAPPLICATIONDELEGATE,></uikit></pre>

AppDelegate.m: 

在代理中我們添加了ScrollView,并將先前的HypnosisView添加到ScrollView中


#import "HypnosisterAppDelegate.h"

import "HypnosisView.h"
@implementation HypnosisterAppDelegate
@synthesize window=_window;

(BOOL)application:(UIApplication )application
  didFinishLaunchingWithOptions:(NSDictionary )launchOptions
{
CGRect wholeWindow = [[self window] bounds];
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:wholeWindow];
  [[self window] addSubview:scrollView];
// 將視圖的大小設為窗口的二倍
  CGRect reallyBigRect;
  reallyBigRect.origin = CGPointZero;
  reallyBigRect.size.width = wholeWindow.size.width  2.0;
  reallyBigRect.size.height = wholeWindow.size.height  2.0;
  [scrollView setContentSize:reallyBigRect.size];
// 在UIScrollView對象里居中
  CGPoint offset;
  offset.x = wholeWindow.size.width  0.5;
  offset.y = wholeWindow.size.height  0.5;
  [scrollView setContentOffset:offset];
// 啟用縮放功能
  [scrollView setMinimumZoomScale:0.5];
  [scrollView setMaximumZoomScale:5];
  [scrollView setDelegate:self];
// 創建視圖
  view = [[HypnosisView alloc] initWithFrame:reallyBigRect];
  [view setBackgroundColor:[UIColor clearColor]];
  [scrollView addSubview:view];
[scrollView release];
[[UIApplication sharedApplication] setStatusBarHidden:YES

                              withAnimation:UIStatusBarAnimationFade];    

[[self window] makeKeyAndVisible];
  return YES;
}

(UIView )viewForZoomingInScrollView:(UIScrollView )scrollView
{
  return view;
}

(void)dealloc
{
  [view release];
  [_window release];
  [super dealloc];
}


@end</pre>





最后運行一下看下效果： 








轉自：http://blog.csdn.net/itachi85/article/details/7726992