MJRefresh自定义下拉刷新动画样式

在使用MJRefresh实现下拉刷新时，经常有自定义刷新动画样式的需求，那么我们就要在MJRefresh库的基础上代码改造，并尽量做到改动工作量最小。

1、新建一个对象，继承自MJRefreshGifHeader

#import "MJRefreshGifHeader.h"

@interface YtGifHeader : MJRefreshGifHeader

@end

2、然后重写方法- (void)prepare，重写后记得实现[super prepare]

#pragma mark - 重写父类的方法
- (void)prepare{
    [super prepare];
    
    // 设置普通状态的动画图片
    NSMutableArray *idleImages = [NSMutableArray array];
    for (NSUInteger i = 1; i<8; i++) {
        UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"load%lu", (unsigned long)i]];
        // 设置Gif的size 对image等比例压缩
        UIImage *newImage = [image imageByScalingToSize:CGSizeMake(75, 65)];
        [idleImages addObject:newImage];
    }
    [self setImages:idleImages forState:MJRefreshStateIdle];
    
    // 设置即将刷新状态的动画图片（一松开就会刷新的状态）
    NSMutableArray *refreshingImages = [NSMutableArray array];
    for (NSUInteger i = 1; i<8; i++) {
        UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"load%lu", (unsigned long)i]];
        // 设置Gif的size 对image等比例压缩
        UIImage *newImage = [image imageByScalingToSize:CGSizeMake(75, 65)];
        [refreshingImages addObject:newImage];
    }
    [self setImages:refreshingImages forState:MJRefreshStatePulling];
    
    // 设置正在刷新状态的动画图片
    [self setImages:refreshingImages forState:MJRefreshStateRefreshing];
    
    //隐藏时间
    self.lastUpdatedTimeLabel.hidden = YES;
    //隐藏状态
    self.stateLabel.hidden = YES;
}

3、在需要下拉刷新的控制器这样实现既可

#import "YtGifHeader.h"

self.tableView.mj_header = [YtGifHeader headerWithRefreshingBlock:^{
        //刷新请求
    }];

注意事项：

mj_header视图展示出来的是GIF原图的大小，如果美工给的切图稍大则效果很丑，那么我们就要在程序中控制GIF动图的Size，思路是对image等比例缩放

1、新建类别UIImage+Extras继承自UIImage

#import <UIKit/UIKit.h>

@interface UIImage (Extras)

- (UIImage *)imageByScalingToSize:(CGSize)targetSize;

@end

2、配置对Image等比例缩放的代码

#import "UIImage+Extras.h"

@implementation UIImage (Extras)

- (UIImage *)imageByScalingToSize:(CGSize)targetSize {
    
    UIImage *sourceImage = self;
    UIImage *newImage = nil;
    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
    
    if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;
        if (widthFactor < heightFactor)
            scaleFactor = widthFactor;
        else
            scaleFactor = heightFactor;
        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;
        // center the image
        if (widthFactor < heightFactor) {            
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
        } else if (widthFactor > heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
    }
    // this is actually the interesting part:
    UIGraphicsBeginImageContext(targetSize);
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    [sourceImage drawInRect:thumbnailRect];
    newImage = UIGraphicsGetImageFromCurrentImageContext(); 
    UIGraphicsEndImageContext(); 
    if(newImage == nil) 
        NSLog(@"could not scale image");   
    return newImage ; 
}

@end

3、调用方法

        // 设置Gif的size 对image等比例压缩
        UIImage *newImage = [image imageByScalingToSize:CGSizeMake(75, 65)];