您好:我在我的应用程序中使用了集合 View ，我注意到使用 reloadData 刷新所需的时间比预期的要长。 .我的收藏 View 有 1 section ，我正在用 5 cell 测试它s(每个都有 2 个按钮和一个标签)。我将一些日志放入我的代码中，以显示系统实际需要多长时间来刷新。有趣的是，日志表明它的刷新速度比现在快。例如，在设备上，它最多需要约 0.2 秒(明显)，但这里是日志:
0.007s从时间 reloadData被叫到时间cellForItemAtIndexPath第一次被称为
0.002s每个单元格加载和返回
0.041s从时间 reloadData被调用到单元格 #5 返回的时间
cellForItemAtIndexPath 中没有什么特别密集的地方函数(基本上只是在 NSArray 的 indexPath 的 row 中找到具有 3 个值的字典)。 然而，即使我删除它并返回一个带有空白按钮的单元格，我也看到了相同的行为。

有没有人知道为什么会发生这种情况？顺便说一下，它只发生在物理设备(iPad Air)上。谢谢!

编辑 #1

根据@brian-nickel 的评论，我使用了 Time Profiler 工具，发现它确实每次都出现峰值 reloadData叫做。这是一个屏幕截图:



@ArtSabintsev，这是围绕 reloadData 的函数调用，然后是 cellForItemAtIndexPath :

//Arrays were just reset, load new data into them
//Loop through each team
for (NSString *team in moveUnitsView.teamsDisplaying) { //CURRENT TEAM WILL COME FIRST

    //Create an array for this team
    NSMutableArray *teamArr = [NSMutableArray new];

    //Loop through all units
    for (int i = [Universal units]; i > 0; i--) {

        //Set the unit type to a string
        NSString *unitType = [Universal unitWithTag:i];

        //Get counts depending on the team
        if ([team isEqualToString:currentTeam.text]) {

            //Get the number of units of this type so that it supports units on transports. If the territory is a sea territory and the current unit is a ground unit, check the units in the transports instead of normal units
            int unitCount = (ter.isSeaTerritory && (i == 1 || i == 2 || i == 8)) ? [self sumOfUnitsInTransportsOfType:unitType onTerritory:ter onTeam:team] : [ter sumOfUnitsOfType:unitType onTeam:team];

            //Get the number of movable units on this territory
            int movableCount = 0;
            if (queue.selectedTerr != nil && queue.selectedTerr != ter) { //This is here to prevent the user from selecting units on another territory while moving units from one territory
                movableCount = 0;
            } else if (ter.isSeaTerritory && (i == 1 || i == 2 || i == 8)) { //Units on transports - can be an enemy territory
                movableCount = [self sumOfUnitsInTransportsOfType:unitType onTerritory:ter onTeam:team];
            } else if ([Universal allianceExistsBetweenTeam:team andTeam:ter.currentOwner] || i == 3 || i == 9) { //Other units - only planes can be on an enemy territory
                movableCount = [ter sumOfMovableUnitsOfType:unitType onTeam:team];
            }

            //See if there are units of this type on this territory on this team
            if (unitCount > 0) {

                //Add data to this team's dictionary
                NSMutableDictionary *unitInfo = [NSMutableDictionary new];
                [unitInfo setObject:@(i) forKey:@"UnitTag"];
                [unitInfo setObject:unitType forKey:@"UnitType"];
                [unitInfo setObject:@(unitCount) forKey:@"Count"];
                [unitInfo setObject:@(movableCount) forKey:@"MovableCount"];
                [unitInfo setObject:team forKey:@"Team"];

                //Add the dictionary
                [teamArr addObject:unitInfo];

                //Increment the counter
                if (unitsOnCT) { //Must check or it could cause a crash
                    *unitsOnCT += 1;
                }
            }
        }
    }

    //Add the team array
    [moveUnitsView.unitData addObject:teamArr];
}

//Reload the data in the collection view
[moveUnitsView.collectionV reloadData];

    //Dequeue a cell
    UnitSelectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"UnitSelectionCell" forIndexPath:indexPath];

    //Get the team array (at the index of the section), then the unit's data (at the index of the row)
    NSMutableDictionary *unitData = (moveUnitsView.unitData[indexPath.section])[indexPath.row];

    //Get values
    int unitTag = [[unitData objectForKey:@"UnitTag"] intValue];
    int count = [[unitData objectForKey:@"Count"] intValue];
    int movableCount = [[unitData objectForKey:@"MovableCount"] intValue];
    NSString *unitType = [unitData objectForKey:@"UnitType"];

    //Set the cell's values
    [cell.upB addTarget:self action:@selector(upMoveUnits:) forControlEvents:UIControlEventTouchUpInside]; [cell.upB setTag:unitTag];
    [cell.iconB setBackgroundImage:[UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[Universal imageNameForUnit:unitType team:[unitData objectForKey:@"Team"]] ofType:nil]] forState:UIControlStateNormal];
    [cell.iconB setTitle:[Universal strForExpDisplay:count] forState:UIControlStateNormal];
    [Universal adjustTitlePlacementOfB:cell.iconB autosize:FALSE]; //Don't autosize because this is a collection view
    cell.unitTypeL.text = unitType;
    cell.unitTypeL.adjustsFontSizeToFitWidth = cell.unitTypeL.adjustsLetterSpacingToFitWidth = TRUE;

    //Set fonts
    [Universal setFontForSubviewsOfView:cell];

    //Return the cell
    return cell;

[moveUnitsView.collectionV registerNib:[UINib nibWithNibName:@"UnitSelectionCell" bundle:nil] forCellWithReuseIdentifier:@"UnitSelectionCell"];

    //Dequeue a cell
    UnitSelectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"UnitSelectionCell" forIndexPath:indexPath];

    //Get the team array (at the index of the section), then the unit's data (at the index of the row)
    NSMutableDictionary *unitData = (moveUnitsView.unitData[indexPath.section])[indexPath.row];

    //Get values
    int unitTag = [[unitData objectForKey:@"UnitTag"] intValue];

    [cell setBackgroundColor:[UIColor redColor]];
    [cell.upB removeTarget:nil action:NULL forControlEvents:UIControlEventTouchUpInside];
    [cell.upB addTarget:self action:@selector(upMoveUnits:) forControlEvents:UIControlEventTouchUpInside]; [cell.upB setTag:unitTag];

    //Return the cell
    return cell;

    if (indexPath.row == [self collectionView:collectionView numberOfItemsInSection:indexPath.section] - 1) {

        [self performSelector:@selector(performMyCPUIntensiveTask:) withObject:myObject afterDelay:0.1];
    }

最佳答案

当您调用 reloadData 时，请确保您在主线程上.

NSLog("on main thread: %@", [NSThread isMainThread] ? @"YES" : @"NO");

dispatch_async(dispatch_get_main_queue(), ^{
    [moveUnitsView.collectionV reloadData];
});

关于ios - UICollectionView reloadData 看起来很慢/滞后(不是即时的)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25614210/