ios - 使用可重复使用的单元格在 iPhone 上缓慢加载表格 View

Question

我从 Parse.com 后端加载数据，他们给我发送了一个使用可重用单元格的解决方案，但现在我仍然遇到加载速度方面的问题，这是我在 tableview 中的编码，我有一个用于制作的子类启动我的单元格 (ExploreStreamCustomCell.m)

    - (ExploreStreamCustomCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
                        object:(PFObject *)object 
{
    static NSString *CellIdentifier = @"ExploreStreamCustomCell";

    ExploreStreamCustomCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[ExploreStreamCustomCell alloc] initWithStyle:UITableViewCellStyleSubtitle 
                                              reuseIdentifier:CellIdentifier];
    }

    // Configure the cell
    cell.listItemTitle.text = [object objectForKey:@"text"];
    cell.checkinsLabel.text = [NSString stringWithFormat:@"%@", [object objectForKey:@"checkins"]];
    cell.descriptionLabel.text = [object objectForKey:@"description"];


    cell.selectionStyle = UITableViewCellSelectionStyleNone;

    PFFile *listThumbnail = [object objectForKey:@"header"];
    cell.listViewImage.image = [UIImage imageNamed:@"loading_image_stream.png"]; // placeholder image
    cell.listViewImage.file = listThumbnail;
    [cell.listViewImage loadInBackground:NULL];

    return cell;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForNextPageAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [super tableView:tableView cellForNextPageAtIndexPath:indexPath];
    cell.textLabel.font = [cell.textLabel.font fontWithSize:kPAWWallPostTableViewFontSize];
    return cell;
}

如果我在单元格中拥有//configure 单元格的所有内容 == nil 它很快但它显示 9 个唯一数据行中的 3 个并重复这 3 个唯一内容单元格 3 次？

在 ExploreStreamCustomCell.m 中编辑额外的代码

#import "ExploreStreamCustomCell.h"

@implementation ExploreStreamCustomCell

@synthesize listViewImage, 
iconLocation, 
iconPeople, 
iconCheckins, 
listItemTitle, 
locationLabel, 
peopleLabel, 
checkinsLabel, 
descriptionLabel,
listItemView;


- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier {
    if(self = [super initWithStyle:style reuseIdentifier:reuseIdentifier]){
        //Initialization code
        listItemView = [[UIView alloc] init];
        listViewImage = [[PFImageView alloc] init];
        iconLocation = [[UIImageView alloc] init];
        iconPeople = [[UIImageView alloc] init];
        iconCheckins = [[UIImageView alloc] init];
        listItemTitle = [[UILabel alloc] init];     
        locationLabel = [[UILabel alloc] init]; 
        peopleLabel = [[UILabel alloc] init];
        checkinsLabel = [[UILabel alloc] init]; 
        descriptionLabel = [[UILabel alloc] init];

        listViewImage.image = [UIImage imageNamed:@"nachtwacht_list_formaat.png"];
        iconLocation.image = [UIImage imageNamed:@"icon_magenta_location.png"];
        iconPeople.image = [UIImage imageNamed:@"icon_magenta_people.png"];
        iconCheckins.image = [UIImage imageNamed:@"icon_magenta_checkins.png"];
        listItemTitle.text = @"text";
        locationLabel.text = @"0,7 km";
        peopleLabel.text = @"34";
        checkinsLabel.text = @"61";
        descriptionLabel.text = @"Description text.";

        [self.contentView addSubview:listItemView];
        [self.contentView addSubview:listViewImage];
        [self.contentView addSubview:iconLocation];
        [self.contentView addSubview:iconPeople];
        [self.contentView addSubview:iconCheckins];
        [self.contentView addSubview:listItemTitle];
        [self.contentView addSubview:locationLabel];
        [self.contentView addSubview:peopleLabel];
        [self.contentView addSubview:checkinsLabel];
        [self.contentView addSubview:descriptionLabel];
    }
    return self;
}

- (void)layoutSubviews {
    [super layoutSubviews];
    CGRect contentRect = self.contentView.bounds;
    CGFloat boundsX = contentRect.origin.x;
    CGRect frame;

    frame= CGRectMake(boundsX+0 , 33, 280, 124);
    listViewImage.frame = frame;
    listViewImage.contentMode = UIViewContentModeScaleAspectFill;
    listViewImage.layer.masksToBounds = YES;

    //listViewImage.backgroundColor = [UIColor lightGrayColor];

    frame= CGRectMake(boundsX+20 , 164, 12, 18);
    iconLocation.frame = frame;
    //iconLocation.backgroundColor = [UIColor lightGrayColor];

    frame= CGRectMake(boundsX+102 , 164, 24, 18);
    iconPeople.frame = frame;
    //iconPeople.backgroundColor = [UIColor lightGrayColor];

    frame= CGRectMake(boundsX+193 , 164, 20, 16);
    iconCheckins.frame = frame;
    //iconLocation.backgroundColor = [UIColor lightGrayColor];

    frame= CGRectMake(boundsX+0 , 0, 280, 33);
    listItemView.frame = frame;
    listItemView.backgroundColor = [UIColor colorWithRed:0.749 green:0.000 blue:0.243 alpha:1.000];


    frame= CGRectMake(boundsX+20 , 3, 240, 29);
    listItemTitle.frame = frame;
    //listItemTitle.textColor = [UIColor colorWithRed:250.0f/255.0f green:194.0f/255.0f blue:9.0f/255.0f alpha:0.8f];
    listItemTitle.textAlignment = UITextAlignmentLeft;
    listItemTitle.font = [UIFont boldSystemFontOfSize:15];
    listItemTitle.textColor = [UIColor whiteColor];
    listItemTitle.backgroundColor = [UIColor clearColor];
    listItemTitle.lineBreakMode = UILineBreakModeTailTruncation;
    //listItemTitle.backgroundColor = [UIColor orangeColor];

    frame= CGRectMake(boundsX+40 , 164, 57, 21);
    locationLabel.frame = frame;
    locationLabel.textAlignment = UITextAlignmentLeft;
    locationLabel.font = [UIFont boldSystemFontOfSize:12];
    locationLabel.textColor = [UIColor colorWithRed:0.749 green:0.000 blue:0.243 alpha:1.000];
    locationLabel.backgroundColor = [UIColor clearColor];
    locationLabel.lineBreakMode = UILineBreakModeTailTruncation;
    locationLabel.numberOfLines = 1;
    //locationLabel.backgroundColor = [UIColor redColor];

    frame= CGRectMake(boundsX+134 , 164, 57, 21);
    peopleLabel.frame = frame;
    peopleLabel.textAlignment = UITextAlignmentLeft;
    peopleLabel.font = [UIFont boldSystemFontOfSize:12];
    peopleLabel.textColor = [UIColor colorWithRed:0.749 green:0.000 blue:0.243 alpha:1.000]; 
    peopleLabel.backgroundColor = [UIColor clearColor];
    peopleLabel.lineBreakMode = UILineBreakModeTailTruncation;
    peopleLabel.numberOfLines = 1;

    frame= CGRectMake(boundsX+221 , 164, 51, 21);
    checkinsLabel.frame = frame;
    checkinsLabel.textAlignment = UITextAlignmentLeft;
    checkinsLabel.font = [UIFont boldSystemFontOfSize:12];
    checkinsLabel.textColor = [UIColor colorWithRed:0.749 green:0.000 blue:0.243 alpha:1.000]; 
    checkinsLabel.backgroundColor = [UIColor clearColor];
    checkinsLabel.lineBreakMode = UILineBreakModeTailTruncation;
    checkinsLabel.numberOfLines = 1;

    frame= CGRectMake(boundsX+0 , 189, 280, 55);
    descriptionLabel.frame = frame;
    descriptionLabel.textAlignment = UITextAlignmentLeft;
    descriptionLabel.font = [UIFont systemFontOfSize:13];
    descriptionLabel.backgroundColor = [UIColor clearColor];
    descriptionLabel.lineBreakMode = UILineBreakModeTailTruncation;
    descriptionLabel.numberOfLines = 3;
}

- (void)setSelected:(BOOL)selected animated:(BOOL)animated {

    [super setSelected:selected animated:animated];

    // Configure the view for the selected state
}


/*
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    // Drawing code
}
*/

@end

Answer 1

探索代码效率低下的一个好方法是使用 Instruments 的 Time Profiler 工具。 Time Profiler 可让您在代码中逐行查看每项任务花费了多少时间。

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我建议使用以下设置进行分析:

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来自 Apple 的人脸检测示例应用:

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然后您可以双击任何一行(更高的百分比意味着更多的时间用于该方法调用)以查看代码中每个地方花费了多少时间。

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从这里开始，您可以开始找出效率低下的地方，并准确了解是什么占用了这么多时间。祝你好运!