obj-c 中的静态背景图片位置（类似于 background-attachment:fixed）

Question

我正在尝试创建一个视图，无论它如何移动，都会将其背景图像保持在同一位置。因此，如果拖动视图，背景会保持不变，类似于 css3 中的background-attachment:fixed。

我的问题是clipsToBounds = YES 似乎不起作用。图像仍然占据整个屏幕并且不会被剪辑到父框架。有什么想法吗？

@implementation StaticBackgroundView {
    UIImageView *imageView;
}

// Must be init'd from code or won't work
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"myImage.png"]];
        imageView.clipsToBounds = YES;
        self.clipsToBounds = YES;

        [self addSubview:imageView];
        [self sendSubviewToBack:imageView];
    }
    return self;
}

- (void) setFrame:(CGRect)frame
{
    // Call the parent class to move the view
    [super setFrame:frame];

    // Do your custom code here.
    NSLog(@"Setframe");
    imageView.frame = CGRectMake(-1*frame.origin.x, frame.origin.y, imageView.frame.size.width, imageView.frame.size.height);
}

Answer 1

每当 StaticBackgroundView 移动时 - 背景图像中心也必须调整。

在下面给出的示例中，每次在 PanGesture 更新期间移动 StaticBackgroundView 时都会调用 updateBackgroundImage。

-(void)updateBackgroundImage
{
    imageView.center = CGPointMake(( (imageView.image.size.width*0.5) - self.center.x) + (self.bounds.size.width*0.5)
                               ,     ((imageView.image.size.height*0.5) - self.center.y) + (self.bounds.size.height*0.5));
}

如果您将 StaticBackgroundView 向右移动，图像将向左移动，并且在 StaticBackgroundView 下方看起来保持静止。

下面的示例代码允许您使用手指移动 StaticBackgroundView 并在下方显示静态图像：

StaticBackgroundView.h

#import <UIKit/UIKit.h>
@interface StaticBackgroundView : UIView
-(void)updateBackgroundImage;
@end

StaticBackgroundView.m

#import "StaticBackgroundView.h"

@implementation StaticBackgroundView {
    UIImageView *imageView;
}

// Must be init'd from code or won't work
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        NSLog(@"StaticBackgroundView:initWithFrame");

        if([[UIDevice currentDevice]userInterfaceIdiom]==UIUserInterfaceIdiomPhone)
        {
            if ([[UIScreen mainScreen] bounds].size.height == 568)
            {
                NSLog(@"iPhone5 image");
                imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"myImage-568h"]];
            }
            else
            {
                NSLog(@"iPhone4 image");
                imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"myImage"]];
            }
        }
        self.clipsToBounds = YES;
        [self updateBackgroundImage];
        [self addSubview:imageView];
        [self sendSubviewToBack:imageView];
    }
    return self;
}

-(void)updateBackgroundImage
{
    imageView.center = CGPointMake(( (imageView.image.size.width*0.5) - self.center.x) + (self.bounds.size.width*0.5)
                               ,     ((imageView.image.size.height*0.5) - self.center.y) + (self.bounds.size.height*0.5));
}

ViewController.m

#import "ViewController.h"
#import "StaticBackgroundView.h"

@interface ViewController ()

@property (strong, nonatomic)  StaticBackgroundView *outletStaticView;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    self.outletStaticView = [[StaticBackgroundView alloc] initWithFrame:CGRectMake(100, 100, 120, 150)];
    [self.view addSubview:self.outletStaticView];

    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];

    [self.outletStaticView addGestureRecognizer:panGestureRecognizer];
}

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


-(void)handlePan:(UIPanGestureRecognizer *)gestureRecognizer
{

    if([gestureRecognizer state] == UIGestureRecognizerStateChanged)
    {

        CGPoint translation = [gestureRecognizer translationInView:self.view];

        gestureRecognizer.view.center = CGPointMake(gestureRecognizer.view.center.x + translation.x, gestureRecognizer.view.center.y + translation.y);

        [gestureRecognizer setTranslation:CGPointMake(0, 0) inView:self.view];

        StaticBackgroundView * theView = (StaticBackgroundView*)gestureRecognizer.view;
        [theView updateBackgroundImage];

    }

}
@end