开发细节(一)

1. iOS6+的UIScrollerView不滚动的问题

• setContentSize方法需要写到viewDidAppear里，而不是viewDidLoad里了。
• scrollEnabled需要设置为YES
• contentSize必须比控件的frame尺寸大
• 当做一些控件滑动效果时，最好是将pagingEnabled设置为NO，autoresizesSubviews最好也设置为NO。

2. 弧度与角度的转换

1角度 = π/180 弧度

1弧度 = 180/π角度

360角度 = 360 * π/180 = 2π弧度 = 一整圈

3. 图片的缩放操作

UIImage *bigImage = [UIImage imageNamed:@"myPhoto"];

CGSize scaleSize = CGSizeMake(80, 80);

//Creates a bitmap-based graphics context and makes it the current context. (创建一个基于位图的context，并设置成当前正使用的context)
UIGraphicsBeginImageContext(scaleSize);

//Draws the entire image in the specified rectangle, scaling it as needed to fit. (在指定的区域內绘制整个图形，并缩放以适应该区域)
[bigImage drawInRect:CGRectMake(0, 0, scaleSize.width, scaleSize.height)];

//Returns an image based on the contents of the current bitmap-based graphics context. (从当前基于位图的context里得到图片)
UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();

//Removes the current bitmap-based graphics context from the top of the stack. (将当前基于位图的context从堆栈移除)
UIGraphicsEndImageContext();

UIImageView *imageView = [[UIImageView alloc] initWithImage:smallImage];
[self.view addSubview:imageView];

4. 画线

CGSize scaleSize = CGSizeMake(200, 200);

UIGraphicsBeginImageContext(scaleSize);

CGContextRef cgContext = UIGraphicsGetCurrentContext();

//style
CGContextSetLineCap(cgContext, kCGLineCapRound);
CGContextSetLineWidth(cgContext, 3.0);
CGContextSetRGBStrokeColor(cgContext, 1.0, 0.0, 1.0, 1.0);

//line 1
CGContextBeginPath(cgContext);
CGContextMoveToPoint(cgContext, 20, 20);
CGContextAddLineToPoint(cgContext, 100, 100);
CGContextStrokePath(cgContext);

//line 2
CGPoint aPoints[3];
aPoints[0] =CGPointMake(100, 80);
aPoints[1] =CGPointMake(130, 80);
aPoints[2] =CGPointMake(60, 140);
CGContextAddLines(cgContext, aPoints, 3);
CGContextDrawPath(cgContext, kCGPathStroke);

CGContextFlush(cgContext);

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
[self.view addSubview:imageView];

5. 随机数的生成

1. 获取一个随机整数范围：0<=rand<100
arc4random() % 100;

2. 获取一个随机整数范围：100<=rand<500
(arc4random() % 101) + 400;

3. 获取一个随机整数，from<=rand<to
- (int)getRandomNumber:(int)from to:(int)to
{
    return (int)(from + (arc4random() % (to – from + 1))); //+1,result is [from to]; else is [from, to)
    
    //from 100 to 500
    //100 + arc4randow()% (500-100+1)
    //100 + arc4random()%401
}

6. 控件的复制

NSData *archivedData = [NSKeyedArchiver archivedDataWithRootObject: myLabel1];

UILabel *myLabel2 = [NSKeyedUnarchiver unarchiveObjectWithData: archivedData];