iOS--UITableViewCell图片的自适应显示

在实际的项目开发过程中，我们经常会遇到图片的处理问题，如果我们的请求结果中包含图片的宽、高，那样处理起来简单很多。一旦请求结果中没有这些信息就显得很操蛋。我们给出一个固定的宽高，又显得展示效果不是那么好。那么只知道图片url的情况下，利用UITableViewCell来显示并进行高度自适应有哪些实现方法呢？
今天我就针对这种情况，把我做知道的两种实现方式：

一、通知####

借助于SDWebImage，其原理很简单，就是在图片显示之后拿到图片的宽高，显示对应图片的cell发送通知，制定对象接受通知后，进行相应的刷新操作。
首先，我们自定义两个类：LGJCellFrameModel和LGJCellModel
LGJCellModel：包含图片的宽，高，URL
LGJCellFrameModel：包含图片的frame，所在cell的高度，LGJCellModel模型对象
其中自定义LGJCellModel的代码：

#import 

@interface LGJCellModel : NSObject

@property (nonatomic ,copy) NSString *url;
@property (nonatomic ,copy) NSString *picW;
@property (nonatomic ,copy) NSString *picH;

-(instancetype)initWithDict:(NSDictionary *)dict;
+(instancetype)modelWithDict:(NSDictionary *)dict;

@end

#import "LGJCellModel.h"

@implementation LGJCellModel

-(instancetype)initWithDict:(NSDictionary *)dict
{
    if (self=[super init]) {
        [self setValuesForKeysWithDictionary:dict];
        
        if (self.url) {
            [self setValue:[NSString stringWithFormat:@"%.0f",kScreenWidth - 20] forKey:@"picW"];
            [self setValue:@"44" forKey:@"picH"];
        }
    }
    return self;
}
+(instancetype)modelWithDict:(NSDictionary *)dict
{
    return [[self alloc] initWithDict:dict];
}
-(void)setValue:(id)value forUndefinedKey:(NSString *)key{
    
}
@end

LGJCellFrameModel的自定义

#import 
#import "LGJCellModel.h"

@interface LGJCellFrameModel : NSObject
@property (nonatomic,assign,readonly) CGRect pictureF;
@property (nonatomic,assign,readonly) CGFloat cellHeight;
@property (nonatomic,strong) LGJCellModel *cellModel;

@end

#import "LGJCellFrameModel.h"
#import "LGJCellModel.h"

@implementation LGJCellFrameModel
-(void)setCellModel:(LGJCellModel *)cellModel
{
    _cellModel=cellModel;

    if (self.cellModel.url) {
        CGFloat pictureX=10;
        CGFloat pictureY=10;
        CGFloat pictureW=[self.cellModel.picW floatValue];
        CGFloat pictureH=[self.cellModel.picH floatValue];
        _pictureF=CGRectMake(pictureX, pictureY, pictureW, pictureH);        
        _cellHeight=CGRectGetMaxY(_pictureF);
    }
    else
    {
        _cellHeight = 0;
    }
}

@end

接下来，我们自定义UITableViewCell

#import 
#import "LGJCellFrameModel.h"
@interface LGJCell : UITableViewCell

@property (nonatomic,strong) LGJCellFrameModel *modelFrame;

-(void)showCellWithModel:(LGJCellFrameModel *)frameModel indexPath:(NSIndexPath *)indexPath;

@end

#import "LGJCell.h"
#import "LGJCellFrameModel.h"
#import "LGJCellModel.h"

@interface LGJCell ()
@property (nonatomic,strong) UIImageView *pictureView;

@end

@implementation LGJCell

-(instancetype)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self=[super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        self.pictureView=[[UIImageView alloc] init];
        [self.contentView addSubview:self.pictureView];
        
    }
    return self;
}
-(void)showCellWithModel:(LGJCellFrameModel *)frameModel indexPath:(NSIndexPath *)indexPath
{
    _modelFrame = frameModel;
    
    [self settingData:(NSIndexPath *)indexPath];
    
    [self settingFrame];
}

-(void)settingData:(NSIndexPath *)tager
{
    LGJCellModel *model=self.modelFrame.cellModel;
    if (model.url) {
        self.pictureView.hidden=NO;
        NSString *imageUrl=[NSString stringWithFormat:@"%@",model.url];
        [self.pictureView sd_setImageWithURL:[NSURL URLWithString:imageUrl] placeholderImage:[UIImage imageNamed:@"[email protected]"] completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                if ([model.picH isEqualToString:@"44"]) {
                NSDictionary *userInfo = @{@"Height" : @(image.size.height*(kScreenWidth-20)/image.size.width),@"indexPath":tager};
                [[NSNotificationCenter defaultCenter] postNotificationName:@"SelectionViewController" object:nil userInfo:userInfo];
            }
        }];
    }
    else
    {
        self.pictureView.hidden=YES;
    }
    
}
-(void)settingFrame
{
    
    if (self.modelFrame.cellModel.url) {
        self.pictureView.frame=self.modelFrame.pictureF;
    }
}
@end

我们在UITableView的dataSource方法- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath中执行：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
        static NSString *ID=@"cellLGJCell";
        LGJCell *cell=[tableView dequeueReusableCellWithIdentifier:ID];
        if (!cell) {
            cell=[[LGJCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:ID];
        }
        else
        {
            for (UIView *sub in cell.contentView.subviews) {
                if ([sub isKindOfClass:[UIImageView class]]) {
                    UIImageView *tempImageView= (UIImageView *)sub;
                    tempImageView.image=nil;
                }
                if ([sub isKindOfClass:[UILabel class]]) {
                    UILabel *tempUILabel= (UILabel *)sub;
                    tempUILabel.text=nil;
                }
            }
        }
        [cell showCellWithModel:self.cellFrames[indexPath.row] indexPath:indexPath];
        cell.userInteractionEnabled = YES;
        
        return cell;
}

并且在对应控制器中注册通知，并实现刷新方法reloadCell：

[[GerneralTool alloc]addObserverWithNames:@[@"SelectionViewController"] selectors:@[@"reloadCell:"] observer:self objects:nil];

-(void)addObserverWithNames:(NSArray *)names selectors:(NSArray *)selectors observer:(id)observer objects:(NSArray *)objects{
    for (int index = 0; index < names.count; index++) {
        NSString *str = selectors[index];
        SEL sel =  NSSelectorFromString(str);
        [[NSNotificationCenter defaultCenter] addObserver:observer selector:sel name:names[index] object:objects[index]];
    }
}

- (void)reloadCell:(NSNotification *)info
{
    NSDictionary *dict=info.userInfo;
    NSString *picHeight=[[dict objectForKey:@"Height"] stringValue];
    NSIndexPath *indexpath=[dict objectForKey:@"indexPath"];
    if ( self.cellFrames.count>=indexpath.row) {
        LGJCellFrameModel *modelFrame=[self.cellFrames objectAtIndex:indexpath.row];
        modelFrame.cellModel.picH=picHeight;
        modelFrame.cellModel=modelFrame.cellModel;
        [self.cellFrames replaceObjectAtIndex:indexpath.row withObject:modelFrame];
        [self.detailView.tableView reloadData];
    }
}

在对应的返回高度的方法中

-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
     LGJCellFrameModel *cellFrame =    self.cellFrames[indexPath.row];
     return cellFrame.cellHeight;
}

二、先下载，后显示####

这里我们需要使用到SDWebImage中SDWebImageDownloader与SDImageCache这两个类来实现功能，分别为图片下载类于图片缓存类。具体代码如下，假设以获取所需图片网址数组为_picArr。
首先借助SDImageCache进行判断对应图片是否缓存。若已缓存，获取其真实需要显示高度（当前屏幕宽度乘图片比例即可），将获取到的高度存入高度字典中。若不存在缓存，使用SDWebImageDownloader进行下载，在下载结束后同样计算高度并缓存图片。SDWebImageDownloader下载图片为异步，无法保证图片按顺序下载完成，因此这里使用字典存储而非数组。字典键值对存储的即为所对应行应显示的高度。

for (NSInteger i = 0; i < _picArr.count; i++) {
        //获取图片网址
        NSString *picUrl = _picArr[i];
        //根据图片网址获取缓存
        UIImage *cachedImage = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey:picUrl];
        if (cachedImage) {//若存在 计算图片真实需要显示高度 存入字典
            CGFloat height = cachedImage.size.height * self.view.bounds.size.width / cachedImage.size.width;
            [_rowHeightDict setObject:[NSNumber numberWithFloat:height] forKey:[NSNumber numberWithInteger:i]];
            dispatch_async(dispatch_get_main_queue(), ^{
                [self.tableView reloadData];
            });
        } else {//不存在缓存 使用SDWebImageDownloader下载
            [[SDWebImageDownloader sharedDownloader]downloadImageWithURL:[NSURL URLWithString:picUrl] options:SDWebImageDownloaderProgressiveDownload progress:^(NSInteger receivedSize, NSInteger expectedSize) {

            } completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
                if (finished) {
                    //对现在图片进行缓存
                    [[SDImageCache sharedImageCache] storeImage:image forKey:picUrl toDisk:YES];
                    CGFloat height = image.size.height * self.view.bounds.size.width / image.size.width;
                    [_rowHeightDict setObject:[NSNumber numberWithFloat:height] forKey:[NSNumber numberWithInteger:i]];
                }
                dispatch_async(dispatch_get_main_queue(), ^{
                    [self.tableView reloadData];
                });
            }];
        }
    }

当前显示的行数需返回行高字典的键值对个数。

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return _rowHeightDict.count;
}

若图片已缓存，加载缓存图片，若无缓存，显示默认placehold图片。

- (UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    MainTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ReusableID];
    UIImage *image = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey:_picArr[indexPath.row]];
    if (!image) {
        cell.photoImageView.image = [UIImage imageNamed:@"placehold"];
    } else {
        cell.photoImageView.image = image;
    }
    return cell;
}

返回行高部分也会相应容易很多，若已计算返回计算好的行高，若无返回默认行高。