ios - 是否可以在 PFImageView 中为新加载的图像设置动画？与 parse.com 相关的 PFImageView

Question

我正在创建一个带有默认图像的 PFImageView。然后我在后台加载图像，当图像从服务器下载完成时，它会立即显示并替换占位符/默认图像。问题是从默认图像到下载图像的过渡不是很愉快。有没有一种方法可以创建淡出默认值并淡入下载的动画？

这是我的代码。

// set the pfImageView into the webView
_pfImageView = [[PFImageView alloc] initWithImage:[UIImage imageNamed:[NSString stringWithFormat:@"%dpTall.jpg", [self.drink.glassId intValue]]]];
_pfImageView.frame = CGRectMake(244, 0, 76, 114);
[webView.scrollView addSubview:_pfImageView];

// create a query for finding images on Parse
PFQuery *query = [PFQuery queryWithClassName:@"Images"];
[query whereKey:@"drinkId" equalTo:[NSNumber numberWithInt:self.drink.primaryKey]];

    [query getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {

    if (!error) {
        PFFile *imageFile = [object objectForKey:@"image"];
        _pfImageView.file = imageFile;
        [_pfImageView loadInBackground];

    } else {
        NSLog(@"PFQuery Error:%@", [error localizedDescription]);
    }
}];

谢谢

Answer 1

我在 PFImageView 上有一个类别，可以在每次出现图像时获得交叉淡入淡出动画:

@implementation PFImageView (Utility)

// Add a fade animation to images
-(void) setImage:(UIImage *)image {
    if ([self.layer animationForKey:KEY_FADE_ANIMATION] == nil) {
        CABasicAnimation *crossFade = [CABasicAnimation animationWithKeyPath:@"contents"];
        crossFade.duration = 0.6;
        crossFade.fromValue  = (__bridge id)(self.image.CGImage);
        crossFade.toValue = (__bridge id)(image.CGImage);
        crossFade.removedOnCompletion = NO;
        [self.layer addAnimation:crossFade forKey:KEY_FADE_ANIMATION];
    }

    [super setImage:image];
}

@end

您只需要一个占位符图像，这样动画就可以在第一时间出现。