iOS GCD 用于 UITableView

Question

我有一个非常密集的 UITableView，需要稍微优化一下。问题是，如何使用大中央站有效地做到这一点。每个单元格都有一个带有几个标签和两个图像的 UIView。我已经对 TableViewCell 进行了子类化，并且 View 正在被重用，尽管当表变大时它仍然有点滞后。我将如何使用 GCD 来优化表格？或者有更好的解决方法吗？我在线程管理方面不是很擅长，正在寻找一些建议。

这是我的表格 View 的代码:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

static NSString *CellIdentifier = @"Cell";
JointCAD *currentCall = [[xmlParser calls] objectAtIndex:indexPath.row];
self.tableView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"texture3.png"]];

TableViewCell *cell = (TableViewCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil)
{
    cell = [[TableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}

cell.callTypeLabel.text = currentCall.currentCallType;
cell.locationLabel.text = currentCall.location;
cell.unitsLabel.text = currentCall.units;
cell.stationLabel.text = [@"Station: " stringByAppendingString:currentCall.station];
cell.selectedBackgroundView = cell.selectionView;

if ([currentCall.callType isEqualToString:@"F"]) {
    cell.imageType = Fire;
}
else {
    cell.imageType = EMS;
}

if ([currentCall.county isEqualToString:@"W"]) {
    cell.imageType1 = Washington;
}
else {
    cell.imageType1 = Clackamas;
}

return cell;
}

这是子类化的 tableviewcell:

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
if (self = [super initWithStyle:style reuseIdentifier:reuseIdentifier]) {

    callView = [[UIView alloc] initWithFrame:CGRectMake(7.5, 7, 305, 65)];
    [callView setAutoresizingMask:UIViewAutoresizingFlexibleLeftMargin |
     UIViewAutoresizingFlexibleRightMargin |
     UIViewAutoresizingFlexibleWidth];
    [callView setContentMode:UIViewContentModeTopLeft];
    [callView setBackgroundColor: [UIColor colorWithRed:240.0/255.0 green:240.0/255.0 blue:240.0/255.0 alpha:1.0]];
    callView.layer.borderWidth = 1.0;
    callView.layer.borderColor = [UIColor colorWithRed:(0/255.0)  green:(0/255.0)  blue:(0/255.0)  alpha:1.0].CGColor;

    [self.contentView addSubview:callView];

    callTypeLabel = [[UILabel alloc]initWithFrame:CGRectMake(5, 2, 190, 21)];
    callTypeLabel.font = [UIFont boldSystemFontOfSize:12.0];
    callTypeLabel.textColor = [UIColor blackColor];
    callTypeLabel.backgroundColor = [UIColor clearColor];
    callTypeLabel.highlightedTextColor = [UIColor whiteColor];
    callTypeLabel.adjustsFontSizeToFitWidth = YES;
    [callView addSubview:callTypeLabel];

    locationLabel = [[UILabel alloc]initWithFrame:CGRectMake(5, 17 , 190, 15)];
    locationLabel.font = [UIFont systemFontOfSize:10.0];
    locationLabel.textColor = [UIColor blackColor];
    locationLabel.backgroundColor = [UIColor clearColor];
    locationLabel.highlightedTextColor = [UIColor whiteColor];
    locationLabel.adjustsFontSizeToFitWidth = YES;
    [callView addSubview:locationLabel];

    unitsLabel = [[UILabel alloc]initWithFrame:CGRectMake(4, 43, 190, 21)];
    unitsLabel.font = [UIFont systemFontOfSize:10.0];
    unitsLabel.textColor = [UIColor blackColor];
    unitsLabel.backgroundColor = [UIColor clearColor];
    unitsLabel.highlightedTextColor = [UIColor whiteColor];
    unitsLabel.adjustsFontSizeToFitWidth = NO;
    [callView addSubview:unitsLabel];

    stationLabel = [[UILabel alloc]initWithFrame:CGRectMake(195 , 25, 75, 20)];
    stationLabel.font = [UIFont systemFontOfSize:12.0];
    stationLabel.textColor = [UIColor blackColor];
    stationLabel.backgroundColor = [UIColor clearColor];
    stationLabel.highlightedTextColor = [UIColor whiteColor];
    stationLabel.adjustsFontSizeToFitWidth = YES;
    [callView addSubview:stationLabel];

    CGRect countyImageFrame = CGRectMake(275, 10, 18, 18);
    UIImageView *countyImageView = [[UIImageView alloc] initWithFrame:countyImageFrame];
    countyImageView.image = countyImage;
    [callView addSubview:countyImageView];

    CGRect callTypeImageFrame = CGRectMake(275, 37, 18, 18);
    UIImageView *callTypeImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
    callTypeImageView.image = callTypeImage;
    [callView addSubview:callTypeImageView];

    selectionView = [[UIView alloc] initWithFrame:CGRectMake(10, 7, 200, 65)];
    [selectionView setBackgroundColor: [UIColor clearColor]];

    }

    return self;
}

- (void)setImageType:(CallType)newImageType {
imageType = newImageType;

if (imageType == Fire) {
    CGRect callTypeImageFrame = CGRectMake(275, 37, 18, 18);
    UIImageView *callTypeImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
    callTypeImageView.image = [UIImage imageNamed:@"red.png"];
    [callView addSubview:callTypeImageView];
}
else if (imageType == EMS) {
    CGRect callTypeImageFrame = CGRectMake(275, 37, 18, 18);
    UIImageView *callTypeImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
    callTypeImageView.image = [UIImage imageNamed:@"yellow.png"];
    [callView addSubview:callTypeImageView];
    }
}

- (void)setImageType1:(County)newImageType1 {
imageType1 = newImageType1;

if (imageType1 == Washington) {
    CGRect callTypeImageFrame = CGRectMake(275, 10, 18, 18);
    UIImageView *countyImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
    countyImageView.image = [UIImage imageNamed:@"blue.png"];
    [callView addSubview:countyImageView];
}
else if (imageType1 == Clackamas) {
    CGRect callTypeImageFrame = CGRectMake(275, 10, 18, 18);
    UIImageView *countyImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
    countyImageView.image = [UIImage imageNamed:@"green.png"];
    [callView addSubview:countyImageView];
    }
}

Answer 1

这有点微妙，但您的代码将挂起的主要区域在 setImageType: 方法中。

您要在此处将以编程方式创建的 ImageView 添加到您的 View 层次结构中:

UIImageView *callTypeImageView = [[UIImageView alloc] initWithFrame:callTypeImageFrame];
callTypeImageView.image = [UIImage imageNamed:@"red.png"];
[callView addSubview:callTypeImageView];

但您实际上并没有删除旧的 ImageView 。更好的方法可能是将创建的 ImageView 缓存在单元格的属性中，然后在设置图像类型时，在创建新 ImageView 之前将消息 -[UIView removeFromSuperview] 发送到旧 ImageView 。

正如您现在的代码所示，每次单元格出列时，都会向其添加一个新的 ImageView ，因此每次用户上下滚动表格 View 时，都会创建一个新的 ImageView 并将其添加到单元格中。很快每个单元格中就会有几十个 ImageView 。我怀疑这导致对 ImageView 的 drawRect 调用比实现您的目的实际需要的调用多很多倍。

更好的方法是将两种类型的 ImageView 作为您在单元格的 init 方法中创建的属性，这些属性仅在 setType 方法中配置。这样，您只需为每种类型创建一个 ImageView ，并在适当的 setType 方法中简单地设置配置其图像。这样做时，请记住 removeFromSuperview 将释放 imageview，因此您必须将其声明为强属性(假设您使用的是 ARC)。

我很欣赏这些解决方案都与 Grand Central Dispatch 没有任何关系，但希望这应该可以解决您的问题，而无需使用大锤来破解螺母:)。