SDAutoLayout学习笔记+原理分析

UITableViewCell图片文本混排

SDAutoLayout学习分析

获取cell高度的原理
在UITableView+SDAutoTableViewCellHeight分类中，使用SDCellAutoHeightManager来对高度进行管理

- (SDCellAutoHeightManager *)cellAutoHeightManager {
    SDCellAutoHeightManager *cellAutoHeightManager = object_getAssociateObject(self, _cmd);
    if (!cellAutoHeightManager) {
        cellAutoHeightManager = [[SDCellAutoHeightManager alloc] init];
        [[self setCellAutoHeightManager: cellAutoHeightManager]];
    }
    return cellAutoHeightManager;
 }
 
 - (void)setCellAutoHeightManager:(SDCellAutoHeightManager *)cellAutoHeightManager{
        objc_setAssociateObject(self, @selector(cellAutoHeightManager), cellAutoHeightManager, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
 }

通过使用runtime的objc_setAssociateObject，objc_getAssociateObject来为当前的tableView添加关联属性的高度管理器SDCellAutoHeightManager

在cell中的设置model方法中，例如DemoVC14Cell.m中

//DemoVC14Cell.m
- (void)setModel:(DemoVC7Model *)model {
    //...设置UI的相关属性
    [self setupAutoHeightWithBottomView:bottomView bottomMargin:10];
}

//UIView+SDAutoHeightWidth
- (void)setupAutoHeightWithBottomView:(UIView *)bottomView bottomMargin:(CGFloat)bottomMargin {
    if(!bottomView) return;
    [self setupAutoHeightWithBottomViewsArray:@[bottomView] bottomMargin:bottomMargin];
}

- (void)setupAutoHeightWithBottomViewsArray:(NSArray *)bottomViewsArray bottomMarigin:(CGFloat)bottomMargin {
    if(!bottomViewsArray) return;
    //清空之前的view
    [self.sd_bottomViewsArray removeAllObjects];
    [self.sd_bottomViewsArray addObjectsFromArray:bottomViewsArray];
    self.sd_bottomViewBottomMargin = bottomMargin;
}
//上面三个方法只有一个目的，那就是确定最底部的view，以及 margin，为后面layoutSubview布局是给autoHeight赋值时做准备。

//DemoVC14.m
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    DemoVC7Model *demoVC14Model = self.modelsArray[indexPath.row];
    return [self.tableView cellHeightForIndexPath:indexPath model:demoVC14Model keyPath:@"model" cellClass:[DemoVC14Cell class] contentViewWidth:[self cellContentViewWidth]];
}

//UITableView+SDAutoTableViewCellHeight
- (CGFloat)cellHeightForIndexPath:(NSIndexPath *)indexPath model:(id)model keyPath:(NSString *)keyPath cellClass:(Class)cellClass contentViewWidth:(CGFloat)contentViewWidth{
    self.cellAutoHeightManager.modelTableview = self;
    self.cellAutoHeightManager.contentViewWidth = contentViewWidth;
    return [self.cellAutoHeightManager cellHeightForIndexPath:indexPath model:model keyPath:keyPath cellClass:cellClass];
}

- (CGFloat)cellHeightForIndexPath:(NSIndexPath *)indexPath model:(id)model keyPath:(NSString *)keyPath
{
    //取已经缓存下的对应的高度，如果有，则直接返回之前计算过的高度
    NSNumber *cacheHeight = [self heightCacheForIndexPath:indexPath];
    if (cacheHeight) {
        return [cacheHeight floatValue];
    } else {
        if (!self.modelCell) {
            return 0;
        }
        
        if (self.modelTableview && self.modelTableview != self.modelCell.sd_tableView) {
            self.modelCell.sd_tableView = self.modelTableview;
        }
        self.modelCell.sd_indexPath = indexPath;
        if (model && keyPath) {
            [self.modelCell setValue:model forKey:keyPath]; //这个地方其实就是调用的setModel方法，在里面会调用上面提到的三个方法
        } else if (self.cellDataSetting) {
            self.cellDataSetting(self.modelCell);
        }
     //...
            
            //调用layoutSubviews方法，由于在UIView+SDAutoLayout分类中已经使用runtime交换了两个方法，所以，会在那里面调用自定义的方法，计算出autoHeight
        [self.modelCell.contentView layoutSubviews];
        //对计算出来的autoHeight进行存储，方便下次调用
        NSString *cacheKey = [self cacheKeyForIndexPath:indexPath];
        [_cacheDictionary setObject:@(self.modelCell.autoHeight) forKey:cacheKey];
        
        if (self.modelCell.sd_indexPath && self.modelCell.sd_tableView) {
            if (self.modelCell.contentView.shouldReadjustFrameBeforeStoreCache) {
                self.modelCell.contentView.height_sd = self.modelCell.autoHeight;
                [self.modelCell.contentView layoutSubviews];
            }
            [self.modelCell.contentView.autoLayoutModelsArray enumerateObjectsUsingBlock:^(SDAutoLayoutModel *model, NSUInteger idx, BOOL *stop) {
            //不太明白这个地方，难道是将每个子视图的frame存储起来，下次直接调用？
                [self.modelTableview.cellAutoHeightManager setSubviewFrameCache:model.needsAutoResizeView.frame WithIndexPath:self.modelCell.sd_indexPath];
            }];
        }
        return self.modelCell.autoHeight;
    }
}

使用runtime交换两个方法

UIView+SDAutoLayout中的load方法

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        NSArray *selStringsArray = @[@"layoutSubviews"];
        
        [selStringsArray enumerateObjectsUsingBlock:^(NSString *selString, NSUInteger idx, BOOL *stop) {
            NSString *mySelString = [@"sd_" stringByAppendingString:selString];
            
            Method originalMethod = class_getInstanceMethod(self, NSSelectorFromString(selString));
            Method myMethod = class_getInstanceMethod(self, NSSelectorFromString(mySelString));
            method_exchangeImplementations(originalMethod, myMethod); //交换系统的layoutSubviews方法与自己定义的sd_layoutSubviews方法
        }];
    });
}

- (void)sd_layoutSubviews {
    [self sd_layoutSubviews];  //由于已经交换了，所以，这行代码会去调用系统自带的layoutSubviews方法
    [self sd_layoutSubviewsHandle]; //执行自己定义的layoutSubviews方法
}

UITableView+SDAutoTableViewCellHeight中的load方法

将tableView中涉及到数据源改变的方法进行自定义交换

+(void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSArray *selStringsArray = @[@"reloadData", @"reloadRowsAtIndexPaths:withRowAnimation:",@"deleteRowsAtIndexPaths:withRowAnimation:",@"insertRowsAtIndexPaths:withRowAnimation:"];
        [selStringsArray enumerateObjectsUsingBlock:^(NSString *selString, NSUInteger idx, BOOL *stop) {
            NSString *mySelString = [@"sd_" stringByAppendingString:selString];
            Method originalMethod = class_getInstanceMethod(self, NSSelectorFromString(selString));
            Method myMethod = class_getInstanceMethod(self, NSSelectorFromString(mySelString));
            method_exchangeImplementtations(originalMethod, myMethod); //交换需要交换的方法
        }];
    });
}

- (void)sd_reloadData {
    if(!self.cellAutoHeightManager.shouldKeepHeightCacheWhenReloadingData) {
        [self.cellAutoHeightManager clearHeightCache]; //清除缓存的高度
    }
    [self sd_reloadData]; //调用系统方法reloadData
    self.cellAutoHeightManager.shouldKeepHeightCacheWhenReloadingData = NO;
}

//...自定义其他需要交换的方法

难道是在返回高度方法调用的时候，将对应的约束条件都存储起来，然后在cellForRow调用的时候再直接使用？

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