iOS開發之自定義View

iOS sdk中的view是UIView，我們可以很方便的自定義一個View。

創建一個 Window-based Application程序，在其中添加一個Hypnosister的類，這個類選擇繼承UIObject。修改這個類，使他繼承：UIView

@interface HypnosisView : UIView

自定義View的關鍵是定義drawRect: 方法，因爲主要是通過重載這個方法，來改變view的外觀。例如，可以使用下面代碼繪製一個很多環中環的效果的view。

- (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);
    }
}

這樣view的效果如下圖：

我們可以繼續繪製一些東西，比如繪製文字，將下面代碼添加帶這個方法後面。

   // 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過大，我們可以把它放置到一個UIScrollView中間，這樣就可以進行拖動了。UIScrollView與View的關係如下圖：

使用下面代碼創建一個比iPhone屏幕大4倍的View，然後通過UIScrollView來展示，代碼如下：

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


//創建一個窗體大小的CGRect
    CGRect wholeWindow = [[self window] bounds];

// 創建一個窗體大小的HypnosisView實例
    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;


}

這樣我們就可以拖動來展示看不到的view了，如下圖：

通過UIScrollView我們還可以設置view的縮放功能，將下面代碼添加到中。這樣我們就可以使用兩根手指縮放view了。

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

總結：文本簡單的總結了一下自定義view的使用。

代碼：Hypnosister.zip