iOS开发之自定义View

 iOS sdk中的view是UIView，我们可以很方便的自定义一个View。

创建一个 Window-based Application程序，在其中添加一个Hypnosister的类，这个类选择继承UIObject。修改这个类，使他继承：UIView

@interface HypnosisView : UIView

自定义View的关键是定义drawRect: 方法，因为主要是通过重载这个方法，来改变view的外观。例如，可以使用下面代码绘制一个很多环中环的效果的view。

View Code

- (void)drawRect:(CGRect)rect 
{
    // What rectangle am I filling?
    CGRect bounds = [self bounds];
    // Where is its center?
    CGPoint center;
    center.x = bounds.origin.x + bounds.size.width / 2.0;
    center.y = bounds.origin.y + bounds.size.height / 2.0;
    // From the center how far out to a corner?
    float maxRadius = hypot(bounds.size.width, bounds.size.height) / 2.0;
    // Get the context being drawn upon
    CGContextRef context = UIGraphicsGetCurrentContext();
    // All lines will be drawn 10 points wide
    CGContextSetLineWidth(context, 10);
    // Set the stroke color to light gray
    [[UIColor lightGrayColor] setStroke];
    // Draw concentric circles from the outside in
    for (float currentRadius = maxRadius; currentRadius > 0; currentRadius -= 20)
    {
        CGContextAddArc(context, center.x, center.y,
                        currentRadius, 0.0, M_PI * 2.0, YES);
        CGContextStrokePath(context);
    }
}

这样view的效果如下图：

我们可以继续绘制一些东西，比如绘制文字，将下面代码添加带这个方法后面。

   // Create a string
    NSString *text = @"我是朱祁林，不是朱麒麟";
    // Get a font to draw it in
    UIFont *font = [UIFont boldSystemFontOfSize:28];
    // Where am I going to draw it?
    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;
    // Set the fill color of the current context to black 
    [[UIColor blackColor] setFill];
    // Set the shadow to be offset 4 points right, 3 points down, 
    // dark gray and with a blur radius of 2 points 
    CGSize offset = CGSizeMake(4, 3);
    CGColorRef color = [[UIColor darkGrayColor] CGColor];
    CGContextSetShadowWithColor(context, offset, 2.0, color);
    // Draw the string
    [text drawInRect:textRect
            withFont:font];

效果：

如果view过大，我们可以把它放置到一个UIScrollView中间，这样就可以进行拖动了。UIScrollView与View的关系如下图：

使用下面代码创建一个比iPhone屏幕大4倍的View，然后通过UIScrollView来展示，代码如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

    
    //创建一个窗体大小的CGRect
    CGRect wholeWindow = [[self window] bounds];
    
    // 创建一个窗体大小的HypnosisView实例
    view = [[HypnosisView alloc] initWithFrame:wholeWindow];
    
    UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:wholeWindow];
    [[self window] addSubview:scrollView];
    // Make your view twice as large as the window
    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];
    CGPoint offset;
    offset.x = wholeWindow.size.width * 0.5;
    offset.y = wholeWindow.size.height * 0.5;
    [scrollView setContentOffset:offset];
    
    // Create the view
    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;
    

}

这样我们就可以拖动来展示看不到的view了，如下图：

通过UIScrollView我们还可以设置view的缩放功能，将下面代码添加到中。这样我们就可以使用两根手指缩放view了。

    // Enable zooming
    [scrollView setMinimumZoomScale:0.5];
    [scrollView setMaximumZoomScale:5];
    [scrollView setDelegate:self];

总结：文本简单的总结了一下自定义view的使用。

代码：Hypnosister.zip