最近在玩"秘密",发现点击主界面的Cell进去后的页面效果不错,就写了个Demo来演示下.

           它主要效果:下拉头部视图放大,上拉视图模糊而且到一定位置固定不动,其他Cell可以继续上移.

@封装的主要效果类:MTHeadEffect.m(.h文件省略,很简单的)

#import "MTHeadEffect.h"
#import <QuartzCore/QuartzCore.h>
#import <Accelerate/Accelerate.h>

// 屏幕的物理宽度
#define ScreenWidth  [UIScreen mainScreen].bounds.size.width
#define HeadViewH  40

CGFloat const kImageOriginHight = 200.f;

@implementation MTHeadEffect

+ (void)viewDidScroll:(UIScrollView *)tableView withHeadView:(UIImageView *)headView withBlur:(CGFloat)blur{

    NSLog(@"y = %f",tableView.contentOffset.y);
    if (tableView.contentOffset.y > kImageOriginHight - HeadViewH) {
        
        headView.frame = CGRectMake(0, -(kImageOriginHight - HeadViewH), ScreenWidth, kImageOriginHight);
        [[UIApplication sharedApplication].keyWindow addSubview:headView];
        
    }else if ((tableView.contentOffset.y < kImageOriginHight - HeadViewH) && tableView.contentOffset.y > 0){
        
        blur = (tableView.contentOffset.y) / 500.0 + 0.45;
        headView.image = [[UIImage imageNamed:@"2"] boxblurImageWithBlur:blur];
        headView.frame = CGRectMake(0, 0, ScreenWidth, kImageOriginHight);
        [tableView addSubview:headView];
        
    }else if (tableView.contentOffset.y <= 0){
        
        // 放大效果---x,y坐标的增量和宽度,高度的增量保持一致
        CGFloat offset  = -tableView.contentOffset.y;
        headView.frame = CGRectMake(-offset,-offset, ScreenWidth+ offset * 2, kImageOriginHight + offset);
        headView.image = [[UIImage imageNamed:@"2"] boxblurImageWithBlur:0.01];
    }
    
}

@end

@implementation UIImage (BlurEffect)

// 为高斯模糊效果封装的一个类目
-(UIImage *)boxblurImageWithBlur:(CGFloat)blur {
    
    NSData *imageData = UIImageJPEGRepresentation(self, 1); // convert to jpeg
    UIImage* destImage = [UIImage imageWithData:imageData];
    
    
    if (blur < 0.f || blur > 1.f) {
        blur = 0.5f;
    }
    int boxSize = (int)(blur * 40);
    boxSize = boxSize - (boxSize % 2) + 1;
    
    CGImageRef img = destImage.CGImage;
    
    vImage_Buffer inBuffer, outBuffer;
    
    vImage_Error error;
    
    void *pixelBuffer;
    
    
    //create vImage_Buffer with data from CGImageRef
    
    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);
    
    
    inBuffer.width = CGImageGetWidth(img);
    inBuffer.height = CGImageGetHeight(img);
    inBuffer.rowBytes = CGImageGetBytesPerRow(img);
    
    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);
    
    //create vImage_Buffer for output
    
    pixelBuffer = malloc(CGImageGetBytesPerRow(img) * CGImageGetHeight(img));
    
    if(pixelBuffer == NULL)
        NSLog(@"No pixelbuffer");
    
    outBuffer.data = pixelBuffer;
    outBuffer.width = CGImageGetWidth(img);
    outBuffer.height = CGImageGetHeight(img);
    outBuffer.rowBytes = CGImageGetBytesPerRow(img);
    
    // Create a third buffer for intermediate processing
    void *pixelBuffer2 = malloc(CGImageGetBytesPerRow(img) * CGImageGetHeight(img));
    vImage_Buffer outBuffer2;
    outBuffer2.data = pixelBuffer2;
    outBuffer2.width = CGImageGetWidth(img);
    outBuffer2.height = CGImageGetHeight(img);
    outBuffer2.rowBytes = CGImageGetBytesPerRow(img);
    
    //perform convolution
    error = vImageBoxConvolve_ARGB8888(&inBuffer, &outBuffer2, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
    if (error) {
        NSLog(@"error from convolution %ld", error);
    }
    error = vImageBoxConvolve_ARGB8888(&outBuffer2, &inBuffer, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
    if (error) {
        NSLog(@"error from convolution %ld", error);
    }
    error = vImageBoxConvolve_ARGB8888(&inBuffer, &outBuffer, NULL, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
    if (error) {
        NSLog(@"error from convolution %ld", error);
    }
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef ctx = CGBitmapContextCreate(outBuffer.data,
                                             outBuffer.width,
                                             outBuffer.height,
                                             8,
                                             outBuffer.rowBytes,
                                             colorSpace,
                                             (CGBitmapInfo)kCGImageAlphaNoneSkipLast);
    CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
    UIImage *returnImage = [UIImage imageWithCGImage:imageRef];
    
    //clean up
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
    
    free(pixelBuffer);
    free(pixelBuffer2);
    CFRelease(inBitmapData);
    
    CGImageRelease(imageRef);
    
    return returnImage;
}


@end

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    // tableView
    self.testTableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 568) style:UITableViewStylePlain];
    self.testTableView.delegate = self;
    self.testTableView.dataSource = self;
    [self.view addSubview:_testTableView];
    
    /**
     *  隐藏状态栏效果
     *  1.系统提供了2种动画,一种是偏移,一种是渐隐
     *  2.在plist文件中将”View controller-based status bar appearance” 设置为 “No”
     */
    [[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation:UIStatusBarAnimationNone];
    
    // headView不作为tableHeadView,而是覆盖在第一个Cell上
    self.headView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 200)];
    self.headView.image = [[UIImage imageNamed:@"2"] boxblurImageWithBlur:0.01];
    self.headView.contentMode = UIViewContentModeScaleAspectFill;  //  图片展示全高度
    self.headView.clipsToBounds = YES;
    [self.testTableView addSubview:self.headView];
    
}

#pragma mark - scroll delegate 头部视图效果方法
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    
    [MTHeadEffect viewDidScroll:scrollView withHeadView:self.headView withBlur:0.01];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{

    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{

    return 25;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{

    if (indexPath.row == 0) {
        return 200;
    }
    return 40;

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    
    static NSString *cellIdentf = @"cell";
    UITableViewCell *cell = [tableView dequeueReusableHeaderFooterViewWithIdentifier:cellIdentf];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentf];
    }
    cell.textLabel.text = [NSString stringWithFormat:@"section = %ld row = %ld",indexPath.section,indexPath.row];
    return cell;

}