新建UIView的子类

大致步骤
1) 新建一个UIView的子类(@interface HypnosisView : UIView)
2) 自定义绘图函数：(void) drawRect:(CGRect)rect

• 确定绘图范围：CGRect bounds=[self bounds]
• 获得CGContext, CGContextRef context=UIGraphicsGetCurrentContext();
• 进行绘图操作

3) 将新视图绑定到主窗口

在HypnosisterAppDelegate中添加一个成员变量HypnosisView *view;

确定绘图范围

在didFinishLaunchingWithOptions中增加子视图:[_window addSubview:view];

进行显示 [_window makeKeyAndVisible];

待确定事项：
1) CGContextStrokePath的功能
2) makeKeyAndVisible消息的功能

关键代码如下：

1) 绑定处理：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    NSLog(@"didFinishLaunchingWithOptions.");
    
    CGRect drawingArea=[_window bounds];
    view = [[HypnosisView alloc] initWithFrame:drawingArea];
    [view setBackgroundColor:[UIColor yellowColor]];
    [_window addSubview:view];
    
    // Override point for customization after application launch.
    [_window makeKeyAndVisible];
    return YES;
}
2) 绘图处理：
- (void) drawRect:(CGRect)rect
{
    
    NSLog(@"Entering the drawing function of HyponsisView.");
    //Get the drawing rectangle
    CGRect bounds=[self bounds];
    
    
    //Calculate the references
    CGPoint center;
    center.x=bounds.origin.x+bounds.size.width/2.0;
    center.y=bounds.origin.y+bounds.size.height/2.0;
    
    float radius=hypot(bounds.size.width, bounds.size.height)/2.0;
    
    //Prepare Drawing
    CGContextRef context=UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context,10);
    [[UIColor greenColor] setStroke];
    
    //Drawing the circles
    for( float r=radius; r>0; r=r-25)
    {
        CGContextAddArc(context, center.x, center.y, r, 0.0, M_PI*2.0,YES);
        CGContextStrokePath(context);
    }
}

运行效果：