iOS项目开发中遇到的问题

1、加载大图，内存崩溃

问题描述：在加载多张高清大图时，会出现崩溃的现象。
解决方案：客户端在显示缩略图时，将宽度大于320的图片，裁剪为宽度为320，高度等比例缩小的图片。

//代码调用方式
[imgView setImageWithURL:[NSURL URLWithString:imageUrl]
                         placeholder:DefaultIcon
                             options:kNilOptions
                             manager:[MGCircleHelper bigImageManager]
                            progress:nil
                           transform:nil
                          completion:nil];

//MGCircleHelper.m
static const CGFloat MGCircleHelperTransformWidthValue = 320;

@implementation MGCircleHelper

+ (YYWebImageManager *)bigImageManager {
    static YYWebImageManager *manager;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSString *path = [[UIApplication sharedApplication].cachesPath stringByAppendingPathComponent:@"migu.bigImage"];
        YYImageCache *cache = [[YYImageCache alloc] initWithPath:path];
        manager = [[YYWebImageManager alloc] initWithCache:cache queue:[YYWebImageManager sharedManager].queue];
        manager.sharedTransformBlock = ^(UIImage *image, NSURL *url) {
            if (!image || image.size.width <= MGCircleHelperTransformWidthValue) {
                return image;
            }
            CGFloat aspectRatio = image.size.width / image.size.height;
            CGFloat resultHeight = MGCircleHelperTransformWidthValue / aspectRatio;
            
            return [image imageByResizeToSize:CGSizeMake(MGCircleHelperTransformWidthValue, resultHeight)]; 
        };
    });
    return manager;
}

@end

2、截图，出现内存泄漏问题

问题描述：排查内存泄漏时，发现网上通用的截屏实现方式，会出现内存泄漏
解决方案：修改截屏的实现方式

 - (UIImage *)screenshot {
     UIWindow *window = [UIApplication sharedApplication].keyWindow;
     UIGraphicsBeginImageContextWithOptions(window.bounds.size, YES, [UIScreen mainScreen].scale);
    [window.layer renderInContext:UIGraphicsGetCurrentContext()]; 
     UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
    return image; 
 } 

改为

- (UIImage *)screenshot {
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    UIGraphicsBeginImageContextWithOptions(window.bounds.size, YES, [UIScreen mainScreen].scale);
    
    [window drawViewHierarchyInRect:window.bounds afterScreenUpdates:YES];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image; 
}

3、实现弹幕功能

技术调研

在github上搜索，找到的stars数比较高的开源三方库为 BarrageRenderer和OCBarrage，因 BarrageRenderer stars数较多，引入到项目中，实测发现在直播时，会出现卡顿的情况。且点击键盘输入弹幕时，在弹出键盘的瞬间，必现卡顿，遂排除掉 BarrageRenderer。选择使用**OCBarrage**来实现弹幕功能。

遇到的问题

引入**OCBarrage**库后发现，业务要求弹幕先在第一条轨道显示，显示不下再在第二条轨道显示，以此类推。此库未提供现成的接口来实现此功能，亦未实现防碰撞功能，阅读其源码发现，在OCBarrageDescriptor类中，有提供一个bindingOriginY属性，来改变弹幕视图Y轴的值。于是尝试自己来实现防碰撞功能。

防碰撞功能实现

//MGCustomLiveBarrageManager.h
#import 

@class MGCustomLivePlayerView;
@interface MGCustomLiveBarrageManager : NSObject 

- (instancetype)init UNAVAILABLE_ATTRIBUTE;

+ (instancetype)new UNAVAILABLE_ATTRIBUTE;

-(instancetype)initWithPlayerContainer:(MGCustomLivePlayerView *)playerContainer;

/**
 显示弹幕
 */
- (void)showBarrage;

/**
 关闭弹幕
 */
- (void)closeBarrage;

@end

//MGCustomLiveBarrageManager.m
static const CGFloat kBarrageDefaultTextSize = 20;
static const CGFloat MGCustomLiveBarrageManagerTopMarge = 3;

@interface MGCustomLiveBarrageManager ()

/**
 视频播放容器
 */
@property (nonatomic, weak) MGCustomLivePlayerView *playerContainer;

@property (nonatomic, strong) OCBarrageManager *barrageManager; 

@end

@implementation MGCustomLiveBarrageManager

#pragma mark - life cycle

- (instancetype)initWithPlayerContainer:(MGCustomLivePlayerView *)playerContainer {
    self = [super init];
    if (self) {
        _playerContainer = playerContainer; 
        _danMuTextSizeRate = [JHPlayerSetting shareInstance].danMuTextSizeRate;
        _danMuSpeed = [JHPlayerSetting shareInstance].danMuSpeed;
        
        [self addListener];
        [self.playerContainer insertSubview:self.barrageManager.renderView atIndex:1];
         
        [self.barrageManager.renderView mas_makeConstraints:^(MASConstraintMaker *make) {
            make.leading.equalTo(self.playerContainer);
            make.trailing.equalTo(self.playerContainer);
            make.top.equalTo(self.playerContainer).offset(44-MGCustomLiveBarrageManagerTopMarge);
            make.bottom.equalTo(self.playerContainer).offset(-49);
        }];
    }
    return self;
}

#pragma mark - public method

- (void)showBarrage {
    [self.barrageManager start];
}

- (void)closeBarrage { 
    [self.barrageManager stop];
}

#pragma mark - private method
//发送弹幕
- (OCBarrageTextDescriptor *)textDescriptorWithContent:(NSString *)content
                                              textSize:(CGFloat)textSize
                                             textColor:(UIColor *)textColor
                                            isSendByMe:(BOOL)isSendByMe {
    if (!content.length || !textColor) {
        return nil;
    }
    
    CGFloat fontSize = textSize * self.danMuTextSizeRate;
    
    NSAttributedString *attributeString = [[NSAttributedString alloc] initWithString:content    attributes:@{NSForegroundColorAttributeName:textColor,NSFontAttributeName:[UIFont systemFontOfSize:fontSize],NSVerticalGlyphFormAttributeName:@0}];
     
    OCBarrageTextDescriptor *bannerDescriptor = [[OCBarrageTextDescriptor alloc] init];
    bannerDescriptor.text = content;
    bannerDescriptor.textColor = textColor;
    bannerDescriptor.attributedText = attributeString;
    
    bannerDescriptor.textFont = [UIFont systemFontOfSize:fontSize];
    bannerDescriptor.positionPriority = isSendByMe?OCBarragePositionVeryHigh: OCBarragePositionMiddle;
    bannerDescriptor.animationDuration = self.danMuSpeed;
    bannerDescriptor.barrageCellClass = [MGBarrageTextCell class];
//设置originY的值
    bannerDescriptor.bindingOriginY = [self bindingOriginY:5];
    if (isSendByMe) {
        bannerDescriptor.borderColor = textColor;
        bannerDescriptor.borderWidth = 1; 
    }
    
    return bannerDescriptor;
}

/**
 * 根据轨道数，获取弹幕的Y轴的值
 */
- (CGFloat)bindingOriginY:(NSUInteger)totalTrackNumber {
    if (totalTrackNumber == 0) {
        return 0;
    }
    
    UIFont *font = [UIFont systemFontOfSize:kBarrageDefaultTextSize * self.danMuTextSizeRate];
    CGFloat lineHeight = font.lineHeight+MGCustomLiveBarrageManagerTopMarge;
    
    NSMutableArray *trackKeys = [NSMutableArray arrayWithCapacity:totalTrackNumber];
    for (NSUInteger i = 0; i < totalTrackNumber; i++) {
        NSString *trackKey = [NSString stringWithFormat:@"track%lu",(unsigned long)i];
        [trackKeys addObject:trackKey];
    }
    
    NSMutableDictionary *trackDictionary = [NSMutableDictionary dictionaryWithCapacity:trackKeys.count];
    
    // 1、根据当前行高，区分正在显示的弹幕
    NSMutableArray *animatingCells = [self.barrageManager.renderView.animatingCells mutableCopy];
    
    for (NSInteger i = 0; i < trackKeys.count; i++) {
        NSMutableArray *lineArray = [NSMutableArray array];
        CGFloat seperateHeight = lineHeight * (i+1);
        
        NSArray *containCells = [animatingCells copy];
        for (OCBarrageCell *barrageCell in containCells) {
            CGFloat maxOrginalX = CGRectGetMaxX(barrageCell.layer.presentationLayer.frame);
            CGFloat minOrginalY = CGRectGetMinY(barrageCell.layer.presentationLayer.frame);
            
            // 保存符合要求的x轴的值
            if (minOrginalY < seperateHeight) {
                [lineArray addObject:@(maxOrginalX)];
                [animatingCells removeObject:barrageCell];
            }
        }
        NSString *key = [trackKeys objectOrNilAtIndex:i];
        [trackDictionary setValue:[lineArray copy] forKey:key];
    }
    
    // 2、根据每条轨道的数组中x轴的值，获取到需要显示的弹幕y轴的值
    CGRect renderViewFrame = self.barrageManager.renderView.frame;
    for (NSInteger i = 0; i < trackKeys.count; i++) {
        NSString *key = [trackKeys objectOrNilAtIndex:i];
        NSArray *lineArray = [trackDictionary objectForKey:key];
        
        __block BOOL fetchResult = YES;
        [lineArray enumerateObjectsUsingBlock:^(NSNumber *  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if ([obj floatValue] > CGRectGetMaxX(renderViewFrame)) {
                fetchResult = NO;
                *stop = YES;
            }
        }];
        if (fetchResult || (lineArray.count == 0)) {
            return [self barrageOriginYWithTrackNumber:i lineHeight:lineHeight];
        }
    }
    NSInteger random = arc4random() % totalTrackNumber;
    return [self barrageOriginYWithTrackNumber:random lineHeight:lineHeight];
}

- (CGFloat)barrageOriginYWithTrackNumber:(NSInteger)trackNumber
                              lineHeight:(CGFloat)lineHeight{
    CGFloat barrageOriginY = trackNumber * lineHeight + MGCustomLiveBarrageManagerTopMarge;
    CGFloat maxY = CGRectGetHeight(self.barrageManager.renderView.frame);
    
    //如果y轴的值，超出了视图范围，提供一个随机值。
    if ((barrageOriginY + lineHeight) > maxY) {
        barrageOriginY = (arc4random()%trackNumber)* lineHeight + MGCustomLiveBarrageManagerTopMarge;;
    }
    return barrageOriginY;
}

@end

小结

在实现过程中，比较耗时的是技术选型和实现防碰撞功能。OCBarrage库整体而言扩展性比较好，代码比较规范。准备去学习一下。