Question

完成这一功能的前提是，你应该先安装好我上一节所说道的 window-Based Application 模版：

教程地址： http://blog.csdn.net/itachi85/article/details/7706549

接着我们要新建一个 window-Based Application 模版

我们创建一个名为 HypnosisView 的 objetctive-C class 文件：

HypnosisView.h:

#import <Foundation/Foundation.h>

@interface HypnosisView : UIView
{

}

@end

HypnosisView.m:
在这个文件中我们加入了绘制了一个同心圆的图形

#import "HypnosisView.h"

@implementation HypnosisView

- (void)drawRect:(CGRect)rect
{
    // 获取绘图区域
    CGRect bounds = [self bounds];

    // 计算中心点
    CGPoint center;
    center.x = bounds.origin.x + bounds.size.width / 2.0;
    center.y = bounds.origin.y + bounds.size.height / 2.0;

    // 计算中心点至边界角的距离
    float maxRadius = hypot(bounds.size.width, bounds.size.height) / 2.0;

    // 获取绘图所需要的上下文
    CGContextRef context = UIGraphicsGetCurrentContext();

    // 用 10 点的宽度来绘制所有的线条
    CGContextSetLineWidth(context, 10);

    // 线条颜色设为淡灰
    [[UIColor lightGrayColor] setStroke];

    // 绘制同心圆
    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.";

    // 获取绘图所需要的字体
    UIFont *font = [UIFont boldSystemFontOfSize:28];

    // 计算绘图位置
    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;

    // 将当前上下文的填充色设为黑色
    [[UIColor blackColor] setFill];

    [text drawInRect:textRect
            withFont:font];
}

@end

接着我们配置代理 AppDelegate.h:

#import <UIKit/UIKit.h>

@class HypnosisView;

@interface HypnosisterAppDelegate : NSObject
    <UIApplicationDelegate, UIScrollViewDelegate> {

    HypnosisView *view;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;

@end

AppDelegate.m:
在代理中我们添加了 ScrollView,并将先前的 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];

    // 将视图的大小设为窗口的二倍
    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 对象里居中
    CGPoint offset;
    offset.x = wholeWindow.size.width * 0.5;
    offset.y = wholeWindow.size.height * 0.5;
    [scrollView setContentOffset:offset];

    // 启用缩放功能
    [scrollView setMinimumZoomScale:0.5];
    [scrollView setMaximumZoomScale:5];
    [scrollView setDelegate:self];

    // 创建视图
    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

最后运行一下看下效果：

http://blog.csdn.net/itachi85/article/details/7706549