ios – 静态子视图背景图像效果

请在sample project查看结果.

为了将来的参考,我将附上以下代码：

ViewController.m

//
//  OSViewController.m
//  ScrollMasks
//
//  Created by #%$^Q& on 11/30/12.
//  Copyright (C) 2012 Demo. All rights reserved.
//

#import "OSViewController.h"

@interface OSViewController ()

// subviews
@property (strong) IBOutlet UIScrollView * scrollView;

// all the subviews
@property (strong) NSArray * maskedSubviews;
// subviews visible at scrollview,we'll update only them
@property (strong) NSArray * visibleMaskedSubviews;

// updates the views from visibleMaskedSubviews
-(void) updateVisibleSubviews;
// updates the visibleMaskedSubviews array with the given scrollView offset
-(void) updateVisibleSubviewsArrayForOffset:(CGPoint) offset;
@end

@implementation OSViewController

-(void) unused {}

#pragma mark - view

-(void) viewWillAppear:(BOOL)animated {
    [self updateVisibleSubviews];
    [super viewWillAppear:animated];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    /*
     See -updateVisibleSubviews comment for the class comments
     */
    UIView * newMaskedView = nil;
    NSMutableArray * newMaskedSubviews = [NSMutableArray array];

    const cGSize scrollViewSize = self.scrollView.bounds.size;
    const int @R_111_10586@lSubviews = 10;
    const float offset = 20.;
    const float height = 100.;

    UIImage * maskImage = [UIImage imagenamed:@"PeeringFrog.jpg"];

    /*

     // Uncomment to compare

     UIImageView * iv = [[UIImageView alloc] initWithFrame:self.scrollView.bounds];
     iv.image = maskImage;
     [self.view insertSubview:iv aTindex:0];
     */

    // add scrollview subviews
    for (int i = 0; i < @R_111_10586@lSubviews; i++) {

        CGRect newViewFrame = CGRectMake(offset,offset*(i+1) + height*i,scrollViewSize.width - offset*2,height);
        newMaskedView = [UIView new];
        newMaskedView.frame = newViewFrame;
        newMaskedView.clipsToBounds = YES;
        newMaskedView.BACkgroundColor = [UIColor redColor];
        newMaskedView.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleWidth;

        UIImageView * maskImageView = [UIImageView new];
        maskImageView.frame = CGRectMake(0,self.scrollView.bounds.size.width,self.scrollView.bounds.size.height);
        maskImageView.image = maskImage;
        [newMaskedView addSubview:maskImageView];

        [self.scrollView addSubview:newMaskedView];
        [newMaskedSubviews addObject:newMaskedView];
    }

    self.scrollView.contentSize = CGSizeMake(scrollViewSize.width,(height+offset)*@R_111_10586@lSubviews + offset*2);

    self.maskedSubviews = [NSArray arrayWithArray:newMaskedSubviews];
    [self updateVisibleSubviewsArrayForOffset:self.scrollView.contentOffset];
}

-(void) updateVisibleSubviews {
    [self updateVisibleSubviewsArrayForOffset:self.scrollView.contentOffset];

    for (UIView * view in self.visibleMaskedSubviews) {

        /*
        TODO:
         view must be UIView subclass with the imageView initializer and imageView frame update method
        */

        CGPoint viewOffset = [self.view convertPoint:CGPointZero fromView:view];
        UIImageView * subview = [[view subviews] objectATindex:0];
        CGRect subviewFrame = subview.frame;
        subviewFrame = CGRectMake(-viewOffset.x,-viewOffset.y,subviewFrame.size.width,subviewFrame.size.height);
        subview.frame = subviewFrame;
    }
}


#pragma mark - scrollview delegate & utilities
-(void) scrollViewDidScroll:(UIScrollView *)scrollView {
    [self updateVisibleSubviews];
}

-(void) updateVisibleSubviewsArrayForOffset:(CGPoint) offset {

    NSMutableArray * newVisibleMaskedSubviews = [NSMutableArray array];
    for (UIView * view in self.maskedSubviews) {
        CGRect intersectionRect = CGRecTintersection(view.frame,self.scrollView.bounds);
        if (NO == CGRectIsNull(intersectionRect)) {
            [newVisibleMaskedSubviews addObject:view];
        }
    }

    self.visibleMaskedSubviews = [NSArray arrayWithArray:newVisibleMaskedSubviews];
}

#pragma mark - memory
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

ViewController.h

//
//  OSViewController.h
//  ScrollMasks
//
//  Created by #%$^Q& on 11/30/12.
//  Copyright (C) 2012 Demo. All rights reserved.
//

/*
 PeeringFrog image is taken (and resized) from Apple sample project "PhotoScroller"
 */

#import <UIKit/UIKit.h>

@interface OSViewController : UIViewController <UIScrollViewDelegate>

@end