IOS 学习笔记（Resize Image,PagedView）PART 14

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之前一篇唠叨的各种疑问，都随着MyEF在上周五通过审核而烟消云散了，可喜可贺！我向EF的老师（Erick）展示了这个程序，他非常开心，还希望我能找时间跟Billy展示一下，我接着又提交了一个版本上去，修正了一些bug，总之，这个第一步已经迈出去了。

[caption id=”” align=”alignnone” width=”384”] 这么看起来，还挺像样子啊~[/caption]

可能是春天的缘故，一些新机会也开始出现，我准备静观其变。又到了要搬家的时候，上周末和白爷一起去顺利的定下了四居室里面的两间，面向消防队，春暖花开。比较头疼的时候，我收拾东西的时候发现，我居然可以收拾出6大箱子以上的东西，不请搬家公司不行了，不知不觉在北京又积存了一堆书。鲜花完毕。

Resize Image

iOS中修改图片尺寸的写法似曾相识，下面列出的办法是保持原图比例的情况下，在中心位置截取正方形的图片：

- (UIImage *)squareImageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    double ratio;
    double delta;
    CGPoint offset;

    //make a new square size, that is the resized imaged width
    CGSize sz = CGSizeMake(newSize.width, newSize.width);

    //figure out if the picture is landscape or portrait, then
    //calculate scale factor and offset
    if (image.size.width > image.size.height) {
        ratio = newSize.width / image.size.width;
        delta = (ratio*image.size.width - ratio*image.size.height);
        offset = CGPointMake(delta/2, 0);
    } else {
        ratio = newSize.width / image.size.height;
        delta = (ratio*image.size.height - ratio*image.size.width);
        offset = CGPointMake(0, delta/2);
    }

    //make the final clipping rect based on the calculated values
    CGRect clipRect = CGRectMake(-offset.x, -offset.y,
                                 (ratio * image.size.width) + delta,
                                 (ratio * image.size.height) + delta);

    //start a new context, with scale factor 0.0 so retina displays get
    //high quality image
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(sz, YES, 0.0);
    } else {
        UIGraphicsBeginImageContext(sz);
    }
    UIRectClip(clipRect);
    [image drawInRect:clipRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

引用文章在此.

AddMask to image

有好几种为图片设置mask的办法，这种是最简单的。首先要准备作为mask的图片,然后做如下的代码操作：

CALayer *mask = [CALayer layer];
mask.contents = (id)[[UIImage imageNamed:@"mask.png"] CGImage];
mask.frame = CGRectMake(0, 0, 100,100);
self.teacherIcon.layer.mask = mask;
self.teacherIcon.layer.masksToBounds = YES;
self.teacherIcon.image = [UIImage imageNamed:@"theImage.png"];

真怀念ActionScript的设置mask的办法啊。

Page View Controller

现在横向滚动页面，一页一页显示的向导视图，一直想做一个，找到一篇很不错的写这个部分的教程,摘录部分思路如下，首先建立要显示内容的控件，方法是在Storyboard上拽一个UIViewController,并指定它的Storyboard ID:

这个UIViewController是用作显示页面内容，可以向拼接任何自定义视图一样调整它，之后又如上图，拽一个PageViewController上去，一样给定Storyboard ID，下面是在代码中组合他们的代码：

self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"GuidePageController"];
self.pageViewController.dataSource = self;
self.pageContentViews = [NSMutableArray array];
GuidePageViewController *pageContent;
for (int i = 1; i < 5; i++) {
    pageContent = [self.storyboard instantiateViewControllerWithIdentifier:@"GuidePageViewController"];
    pageContent.imageFileName = [NSString stringWithFormat:@"GuidePage%d.png",i];
    pageContent.index = i - 1;
    if (i == 4) {
        pageContent.parentView = self;
    }
    [self.pageContentViews addObject:pageContent];
}
[self.pageViewController setViewControllers:@[self.pageContentViews[0]] direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
[self addChildViewController:_pageViewController];
[self.view addSubview:_pageViewController.view];
[self.pageViewController didMoveToParentViewController:self];

Storyboard ID的作用是，可以利用storyboard对象的instantiateViewControllerWithIdentifier方法创建视图对象。接下来要实现UIPageViewControllerDataSource的对应方法：

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController {
    // The number of items reflected in the page indicator.
    return self.pageContentViews.count;
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController {
    // The selected item reflected in the page indicator.
    return 0;
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {

    NSUInteger index = [(GuidePageViewController *)viewController index];

    if (index == 0) {
        return nil;
    }

    index--;

    return [self.pageContentViews objectAtIndex:index];

}
//
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    NSUInteger index = [(GuidePageViewController *)viewController index];

    index++;

    if (index == self.pageContentViews.count) {
        return nil;
    }
    return [self.pageContentViews objectAtIndex:index];
}

效果如下：

最后，牙疼真要命！