使用每个 UIImageView 的 UIActivityIndi​​catorView 将 UIImageView 从 URL 加载到 UIScrollView

Question

我有以下代码，可以正常工作 UIScrollView。但是加载图片时只能在最后一个子视图中看到，并且 UIActivityIndi​​catorView 无法加载每张图片。

对于这样的任务该怎么做呢？

myProject2ViewController.h

#import <UIKit/UIKit.h>
#import "PageScrollView.h"

@interface myProject2ViewController : UIViewController
{
    NSMutableArray *pages;
    PageScrollView *scrollView;
    UIView *myOneSubview;
    UIImageView *imageView;
    UIActivityIndicatorView *myIndicator;
}

@property (nonatomic, retain) PageScrollView *scrollView;
@property (nonatomic, retain) UIImageView *imageView;
@property (nonatomic, retain) UIActivityIndicatorView *myIndicator;

@end

myProject2ViewController.m

#import "myProject2ViewController.h"

@implementation myProject2ViewController

@synthesize scrollView;
@synthesize imageView;
@synthesize myIndicator;

- (void)dealloc
{
    [super dealloc];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSArray *imageUrls = [NSArray arrayWithObjects:
                          @"link_1",
                          @"link_2",
                          @"link_3",
                          nil];

    pages = [[NSMutableArray alloc] init];

    for (int i = 0; i < [imageUrls count]; i++) {

        CGRect frameOne = CGRectMake(0.0f, 50.0f, 320.0f, 416.0f);
        myOneSubview = [[UIView alloc] initWithFrame:frameOne];
        myOneSubview.backgroundColor = [UIColor blackColor];

        NSString *imageUrl = [imageUrls objectAtIndex:i];

        myIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
        myIndicator.center = CGPointMake(160.0f, 130.0f);
        myIndicator.hidesWhenStopped = YES;
        myIndicator.backgroundColor = [UIColor clearColor];

        imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0.0f, 50.0f, 320.0f, 416.0f)];

        [NSThread detachNewThreadSelector:@selector(loadImages:) toTarget:self withObject:imageUrl];

        [myOneSubview addSubview:imageView];

        [pages addObject:myOneSubview];
    }

    scrollView = [[PageScrollView alloc] initWithFrame:self.view.frame];
    scrollView.pages = pages;
    scrollView.delegate = self;
    self.view = scrollView;
}

- (void)loadImages:(NSString *)string
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    [myIndicator startAnimating];

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;


    NSData *imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:string]];
    UIImage *image = [[UIImage alloc] initWithData:imageData];
    [imageView setImage:image];

    [image release];
    [imageData release];

    [self performSelectorOnMainThread:@selector(loadImageComplete) withObject:self waitUntilDone:YES];

    [pool drain];
}

-(void)loadImageComplete
{
    NSLog(@"Load image complete!");
    [myIndicator stopAnimating];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

@end

Answer 1

当您这样做时：

CGRectMake(0.0f, 50.0f, 320.0f, 416.0f);

在 for 循环内，您为在 for 循环中创建的每个图像指定相同的精确位置和尺寸。换句话说，您创建的每个下一个图像都将位于上一个图像之上，因此，您只能看到在 for 循环中创建的最终图像。

尝试将计数器“i”变量添加到 CGRectMake() 中的 X 和 Y 值，以偏移随后创建的每个图像。

因此，假设每个图像都是 100 像素 x 100 像素，那么类似于：

CGRectMake(0.0f + (i * 100.0f), 50.0f, 320.0f, 416.0f);

将使每个图像紧邻前一个图像（因为每个图像都是 100 像素宽，所以我们将其偏移 100 像素，并使用该值作为下一张图片）。如果您在 (i * 100) 之后添加一个额外的值，使其变为 (i * 100 + 50)，那么这将为您提供距前一个图像 50 像素的左填充。

如果您的图像尺寸不同，您需要事先计算图像的宽度和高度，并将其纳入您的 CGRectMake() 方法中。

希望有帮助。

此外，您可以编写如下代码，而不是创建如此多的视图来添加到滚动视图中：

scrollView = [[UIScrollview alloc] init];

. . .

for(...)
{
    UIImageView *currentImage = [[UIImageView alloc] initWithFrame:CGRectMake(0.0f + (i * 100.0f), 50.0f, 320.0f, 416.0f);
    [currentImage setImage:[UIImage imageNamed:[imageUrls objectAtIndex:i]]];

    . . .

    [scrollView addSubview: currentImage];
    [currentImage release];
}