我想获得一些关于下面所示代码的建议。滚动在 iPhone 上有点慢，但在模拟器上则不然。我想做的是在每行上显示多个小时和消息，并且每行可能有不同的小时数和消息。
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// message + hours
static NSString *CellIdentifier = @"Cell1";
// others
static NSString *CellIdentifier1 = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
UITableViewCell *cell1 = [tableView dequeueReusableCellWithIdentifier:CellIdentifier1];
UILabel *hoursLabel;
UILabel *infoLabel;
UILabel *dayLabel;
switch (indexPath.section) {
case 0:
cell1 = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier1] autorelease];
if ([hoursArray count] > 0 && [infoArray count] > 0) {
harray = [self seperateString:[hoursArray objectAtIndex:indexPath.row]];
iarray = [self seperateString:[infoArray objectAtIndex:indexPath.row]];
// check how many hours in an array
int loop = [harray count];
int currentInfoHeight = 0;
int currentHourHeight = 0;
int labelHeight = 0;
for (int i = 0; i < loop ; i++) {
NSString *Text = [[NSString alloc] initWithFormat:@"%@", [harray objectAtIndex:i]];
NSString *Text1 = [[NSString alloc] initWithFormat:@"%@", [iarray objectAtIndex:i]];
UIFont *cellFont = [UIFont systemFontOfSize:hourfontSize];
UIFont *cellFont1 = [UIFont systemFontOfSize:messageFontSize];
CGSize constraintSize = CGSizeMake(180.0f, MAXFLOAT);
CGSize labelSize = [Text sizeWithFont:cellFont constrainedToSize:constraintSize lineBreakMode:UILineBreakModeWordWrap];
CGSize labelSize1 = [Text1 sizeWithFont:cellFont1 constrainedToSize:constraintSize lineBreakMode:UILineBreakModeWordWrap];
/* HourLabel */
hoursLabel =
[[[UILabel alloc]
initWithFrame:
CGRectMake(
70.0 + 2.0 * cell1.indentationWidth,
currentHourHeight + gap,
tableView.bounds.size.width - 70.0 - 4.0 * cell1.indentationWidth,
labelSize.height)]
autorelease];
hoursLabel.text = [NSString stringWithFormat:[harray objectAtIndex:i]];
hoursLabel.backgroundColor = [UIColor clearColor];
hoursLabel.textColor = [UIColor blackColor];
// hoursLabel.shadowColor = [UIColor blackColor];
// hoursLabel.shadowOffset = CGSizeMake(0, 1);
hoursLabel.font = [UIFont systemFontOfSize:hourfontSize];
[cell1.contentView addSubview:hoursLabel];
if (![[iarray objectAtIndex:i] isEqualToString:@"-"]) {
/* infoLabel */
infoLabel =
[[[UILabel alloc]
initWithFrame:
CGRectMake(
70.0 + 2.0 * cell1.indentationWidth,
currentInfoHeight + gap + labelSize.height,
tableView.bounds.size.width - 70.0 - 4.0 * cell1.indentationWidth,
labelSize1.height)]
autorelease];
infoLabel.text = [NSString stringWithFormat:[iarray objectAtIndex:i]];
infoLabel.numberOfLines = 0;
infoLabel.backgroundColor = [UIColor clearColor];
infoLabel.textColor = [UIColor colorWithRed:51.0/255 green:51.0/255.0 blue:51.0/255.0 alpha:1.0];
infoLabel.font = [UIFont systemFontOfSize:messageFontSize];
[cell1.contentView addSubview:infoLabel];
labelHeight = (infoLabel.bounds.size.height);
}
else
{
labelHeight=0;
}
/* store current height of label */
currentHourHeight = (hoursLabel.bounds.size.height) + labelHeight + gap + currentHourHeight;
currentInfoHeight = (hoursLabel.bounds.size.height) + labelHeight + gap + currentInfoHeight;
}
}
/* dayLabel */
dayLabel =
[[[UILabel alloc]
initWithFrame:
CGRectMake(
2.0 * cell1.indentationWidth,
[self tableView:tableView_ heightForRowAtIndexPath:indexPath] / 2.0f - dayFontSize/2 ,
tableView.bounds.size.width -
70.0 - 4.0 * cell1.indentationWidth,
dayFontSize)]
autorelease];
[cell1.contentView addSubview:dayLabel];
/* Configure the properties for the text that are the same on every row */
dayLabel.backgroundColor = [UIColor clearColor];
dayLabel.textColor = [UIColor colorWithRed:207.0/255 green:181.0/255.0 blue:59.0/255.0 alpha:1.0];
dayLabel.font = [UIFont boldSystemFontOfSize:dayFontSize];
/* Draw a line to divide info and message into two sections */
UIView *lineView = [[[UIView alloc] initWithFrame:CGRectMake(79, 0, 1.5, cell1.contentView.bounds.size.height)] autorelease];
lineView.backgroundColor = [self.tableView_ separatorColor];
lineView.autoresizingMask = 0x3f;
[cell1.contentView addSubview:lineView];
NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
[formatter setDateFormat:@"EEE"];
dayLabel.text = [NSString stringWithFormat:[daysArray objectAtIndex:[indexPath row]]];
[cell1 setSelectionStyle:UITableViewCellSelectionStyleNone];
return cell1;
case 1:
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text = @"View information for this location";
cell.textLabel.font = [UIFont systemFontOfSize:16];
cell.textLabel.textAlignment = UITextAlignmentCenter;
return cell;
case 2:
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text = @"Show building on campus map";
cell.textLabel.font = [UIFont systemFontOfSize:16];
cell.textLabel.textAlignment = UITextAlignmentCenter;
return cell;
case 3:
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text = @"Direction to building";
cell.textLabel.font = [UIFont systemFontOfSize:16];
cell.textLabel.textAlignment = UITextAlignmentCenter;
return cell;
default:
break;
}
return cell;
}
最佳答案
您正在为每个单元格分配一个 NSDateFormatter。根据我的经验，NSDateFormatter 分配和配置是一些最昂贵的调用。它们需要大量时间。
使 NSDateFormatter 成为一个实例变量，这样您就必须准确地分配和配置它一次。您没有重复使用您的细胞。如果您不重复使用单元格，您的性能将会受到影响。 重用的模式是这样的:
.
- (NSDateFormatter *)weekDayDateFormatter {
if (!myWeekDayDateFormatter) {
myWeekDayDateFormatter = [[NSDateFormatter alloc] init];
[myWeekDayDateFormatter setDateFormat:@"EEE"];
}
return myWeekDayDateFormatter;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSInteger secondLabelTag = 1001;
static NSInteger imageViewTag = 1002;
static NSString *CellIdentifier1 = @"Cell1";
static NSString *CellIdentifier2 = @"Cell2";
UITableViewCell *cell = nil;
switch (indexPath.section) {
case 0: {
cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier1];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier1];
// allocate subviews and configure properties that never change
UILabel *secondLabel = [[UILabel alloc] initWithFrame:CGRectZero];
secondLabel.tag = secondLabelTag;
secondLabel.textColor = [UIColor orangeColor];
[cell.contentView addSubview:secondLabel];
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectZero];
imageView.tag = imageViewTag;
imageView.contentMode = UIViewContentModeScaleAspectFill;
[cell.contentView addSubview:imageView];
}
// Whatever happened before you have a valid cell here
UILabel *secondLabel = (UILabel *)[cell.contentView viewWithTag:secondLabelTag];
UIImageView *imageView = (UIImageView *)[cell.contentView viewWithTag:imageViewTag];
secondLabel.text = [self.weekDayDateFormatter stringFromDate:[dataSource objectAtIndex:indexPath.row]];
imageView.image = [dataSource objectAtIndex:indexPath.row];
break;
}
case 1: {
cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier2];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier2];
// configure properties that never change between cells
cell.textLabel.textColor = [UIColor greenColor];
cell.selectionStyle = UITableViewCellSelectionStyleGray;
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
}
// configure properties that are different between cells
cell.textLabel.text = [dataSource objectAtIndex:indexPath.row];
cell.textLabel.backgroundColor = [dataSource objectAtIndex:indexPath.row];
break;
}
}
每次调用的tableView:cellForRowAtIndexPath:部分中的代码应该尽可能快地执行。在滚动期间，每个单元格都会调用此方法。
关于ios - UITableViewCell 上的自定义 subview 和滚动问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9816535/