iOS小知识集合

1. 局部圆角

    CGRect rect = CGRectMake(0, 0, 100, 50);
    CGSize radio = CGSizeMake(5, 5);//圆角尺寸
    UIRectCorner corner = UIRectCornerTopLeft|UIRectCornerTopRight;//这只圆角位置
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:corner cornerRadii:radio];
    CAShapeLayer *masklayer = [[CAShapeLayer alloc]init];//创建shapelayer
    masklayer.frame = button.bounds;
    masklayer.path = path.CGPath;//设置路径
    button.layer.mask = masklayer;

2. 给WebView添加头视图方便一起滚动

    UIView *webBrowserView = self.webView.scrollView.subviews[0];//拿到webView的webBrowserView
    self.backHeadImageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, kScreenWidth,kScreenWidth*2/3.0)];
    [_backHeadImageView sd_setImageWithURL:[NSURL URLWithString:self.imageUrl] placeholderImage:[UIImageimageNamed:@"placeholderImage"]];
    [self.webView insertSubview:_backHeadImageView belowSubview:self.webView.scrollView];
    //把backHeadImageView插入到webView的scrollView下面
    CGRect frame = self.webBrowserView.frame;
    frame.origin.y = CGRectGetMaxY(_backHeadImageView.frame);
    self.webBrowserView.frame = frame;
    //更改webBrowserView的frame向下移backHeadImageView的高度，使其可见

3. 设置模态跳转动画

    DetailViewController *detailVC = [[DetailViewController alloc]init];
    //UIModalTransitionStyleFlipHorizontal 翻转
    //UIModalTransitionStyleCoverVertical 底部滑出
    //UIModalTransitionStyleCrossDissolve 渐显
    //UIModalTransitionStylePartialCurl 翻页
    detailVC.modalTransitionStyle = UIModalTransitionStylePartialCurl;
    [self presentViewController:detailVC animated:YES completion:nil];

4. 给UIView设置图片

    UIImage *image = [UIImage imageNamed:@"playing"];
    _layerView.layer.contents = (__bridge id)image.CGImage;
    _layerView.layer.contentsCenter = CGRectMake(0.25, 0.25, 0.5, 0.5);//啥意思？先看书吧。contentsRect
    _layerView.contentsGravity = kCAGravityResize;

5. 给TableView或者CollectionView的cell添加简单动画

  - (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath*)indexPath{
    NSArray *array =  tableView.indexPathsForVisibleRows;
    NSIndexPath *firstIndexPath = array[0];
    //设置anchorPoint
    cell.layer.anchorPoint = CGPointMake(0, 0.5);
    //为了防止cell视图移动，重新把cell放回原来的位置
    cell.layer.position = CGPointMake(0, cell.layer.position.y);
    //设置cell 按照z轴旋转90度，注意是弧度
    if (firstIndexPath.row < indexPath.row) {
        cell.layer.transform = CATransform3DMakeRotation(M_PI_2, 0, 0, 1.0);
    }else{
        cell.layer.transform = CATransform3DMakeRotation(- M_PI_2, 0, 0, 1.0);
    }
    cell.alpha = 0.0;
    [UIView animateWithDuration:1 animations:^{
        cell.layer.transform = CATransform3DIdentity;
        cell.alpha = 1.0;
    }];
}

6. “别挤我”和“紧抱我”
   我们都知道，UIButton和UILabel，在布局时并不需要给它们设置宽高约束，因为他们可以根据自身内容决定大小（intrinsic size）。但是当两个label的intrinsic size加起来比superview还要大或者小的时候，那么label就可能会受到压缩或者拉伸。也就引出了“Content Compression Resistance Priority（别挤我）”和“Content Hugging Priority（紧抱我）”，即通过设置优先级来决定拉伸或者压缩哪个label。
   比如：两个label的size加起来比superview小，那么label1“Content Compression Resistance Priority”值比label2“Content Compression Resistance Priority”值大，那么就会压缩label2。