Question

我的表滚动速度非常慢，我认为它是由我的cellForRowAtIndexPath中的Core Data方法引起的。下面是我的cellForRowAtIndexPath方法：

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

static NSString *CellIdentifier = @"Cell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}

NSManagedObject *info = [buildingArray objectAtIndex: [indexPath row]];
// all rooms have been scanned for building
if([self allRoomsScanned: [[info valueForKey:@"buildingid"] intValue]]) {
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
    [cell.textLabel setTextColor: [UIColor lightGrayColor]];
}
else {
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    [cell.textLabel setTextColor: [UIColor blackColor]];
}
[cell.textLabel setFont:[UIFont fontWithName:@"Helvetica-Bold" size:16.0]];
[cell.textLabel setText:[info valueForKey:@"buildingname"]];

return cell;
}

这是allRoomsScanned方法和allDevicesScanned方法：

- (BOOL) allRoomsScanned: (int) buildingID {
NSMutableArray *scannedRoomArray = [[NSMutableArray alloc] init];
// Get all user_device
NSManagedObjectContext *context = [self managedObjectContext];
NSError *error;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:@"user_device" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
NSNumber *deviceid = [NSNumber numberWithInt: 0];
NSNumber *roomid = [NSNumber numberWithInt: 0];
//int lastRoomID = 0;

for (NSManagedObject *info in fetchedObjects) {
    // Get all device
    deviceid = [info valueForKey:@"deviceid"];
    fetchRequest = [[NSFetchRequest alloc] init];
    entity = [NSEntityDescription 
              entityForName:@"device" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(deviceid = %d)", [deviceid intValue]];
    [fetchRequest setPredicate:predicate]; 
    NSArray *fetchedDevices = [context executeFetchRequest:fetchRequest error:&error];
    for (NSManagedObject *infod in fetchedDevices) {
        // Get all room
        roomid = [infod valueForKey:@"roomid"];
        fetchRequest = [[NSFetchRequest alloc] init];
        entity = [NSEntityDescription 
                  entityForName:@"room" inManagedObjectContext:context];
        [fetchRequest setEntity:entity];

        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(roomid = %d) AND (buildingid = %d)", [roomid intValue], buildingID];
        [fetchRequest setPredicate:predicate]; 
        NSMutableArray *fetchedRoom = [[context executeFetchRequest:fetchRequest error:&error] mutableCopy];

        // add room to array if room belongs to selected building and room not already added
        if([fetchedRoom count] > 0) { //&& lastRoomID != [roomid intValue]) {
            for (NSManagedObject *info in fetchedRoom) {
                NSLog(@"room id: %@", [info valueForKey:@"roomid"]);
                // add room ids to array if not already there
                if (![scannedRoomArray containsObject:[info valueForKey:@"roomid"]] && [self allDevicesScanned:[[info valueForKey:@"roomid"] intValue]])
                    [scannedRoomArray addObject: [info valueForKey:@"roomid"]];
            }
            //lastRoomID = [roomid intValue];
        }
    }
}

fetchRequest = [[NSFetchRequest alloc] init];
entity = [NSEntityDescription 
          entityForName:@"room" inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(buildingid = %d)", buildingID];
[fetchRequest setPredicate:predicate]; 
NSArray *fetchedRoomTotal = [context executeFetchRequest:fetchRequest error:&error];
//NSLog(@"Total Rooms for Building: %d", [fetchedRoomTotal count]);
//NSLog(@"Scanned Rooms for Building: %d", [scannedRoomArray count]);
//NSLog(@"Scanned rooms: %@", scannedRoomArray);
if([fetchedRoomTotal count] == [scannedRoomArray count] && [fetchedRoomTotal count] > 0) {
    return YES;
}
else {
    return NO;
}
}

- (BOOL) allDevicesScanned: (int) roomID {
NSMutableArray *scannedDeviceArray = [[NSMutableArray alloc] init];
// Get all user_device
NSManagedObjectContext *context = [self managedObjectContext];
NSError *error;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:@"user_device" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
NSNumber *deviceid = [NSNumber numberWithInt: 0];
//NSNumber *roomid = [NSNumber numberWithInt: 0];

for (NSManagedObject *info in fetchedObjects) {
    // Get all device
    deviceid = [info valueForKey:@"deviceid"];
    fetchRequest = [[NSFetchRequest alloc] init];
    entity = [NSEntityDescription 
              entityForName:@"device" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(deviceid = %d) AND (roomid = %d)", [deviceid intValue], roomID];
    [fetchRequest setPredicate:predicate]; 
    NSArray *fetchedDevices = [context executeFetchRequest:fetchRequest error:&error];
    for (NSManagedObject *infod in fetchedDevices) {

        // add device to array
        if([fetchedDevices count] > 0) {
            NSLog(@"room id: %d", roomID);
            // add device ids to array if not already there
            if (![scannedDeviceArray containsObject:deviceid])
                [scannedDeviceArray addObject: deviceid];
        }
    }
}

fetchRequest = [[NSFetchRequest alloc] init];
entity = [NSEntityDescription 
          entityForName:@"device" inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(roomid = %d)", roomID];
[fetchRequest setPredicate:predicate]; 
NSArray *fetchedDeviceTotal = [context executeFetchRequest:fetchRequest error:&error];
//NSLog(@"Total Devices for Room: %d", [fetchedDeviceTotal count]);
//NSLog(@"Scanned Devices for Room: %d", [scannedDeviceArray count]);
//NSLog(@"Scanned Devices: %@", scannedDeviceArray);
if([fetchedDeviceTotal count] == [scannedDeviceArray count] && [fetchedDeviceTotal count] > 0) {
    return YES;
}
else {
    return NO;
}
}

关于如何在滚动时摆脱延迟的任何想法？我假设我可能使用我的核心数据调用或我在cellForRowAtIndexPath中调用方法的方式效率低下。

感谢您的帮助。非常感谢。

Answer 1

在滚动表视图时，您确实不应该在主线程上进行获取请求和处理。正如rokjarc所说，你绝对应该保存你的（非常重）allRoomsScanned方法的结果。我建议添加一个新样式，即带有活动指示符，当你还没有输入结果时，单元格会得到。加载完成后，立即刷新表格视图单元格。

注意：您无法在allRoomsScanned和allDevicesScanned中使用默认的NSManagedObjectContext。 您需要在后台线程中初始化新的上下文。在块的开头初始化新的上下文并将其作为方法参数传递或在方法中创建一个新的上下文。

NSManagedObject *info = [buildingArray objectAtIndex: [indexPath row]];

NSNumber *cachedResult = [self.scanResults objectForKey:info.objectID];
if (cachedResult == nil) {
    // style loading state

    int scanInfo = [[info valueForKey:@"buildingid"] intValue];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        BOOL result = [self allRoomsScanned: scanInfo];
        [self.scanResults setObject:[NSNumber numberWithBool:result] forKey:info.objectID];
        [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic]
    });

} else if (cachedResult.boolValue == YES) {
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
    [cell.textLabel setTextColor: [UIColor lightGrayColor]];
} else if (cachedResult.boolValue == NO) {
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    [cell.textLabel setTextColor: [UIColor blackColor]];
}

[cell.textLabel setFont:[UIFont fontWithName:@"Helvetica-Bold" size:16.0]];
[cell.textLabel setText:[info valueForKey:@"buildingname"]];

return cell;

UITableView cellForRowAtIndexPath导致慢滚动

1 个答案: