Question

我正在使用UIScrollView显示多个图像。但我希望它能自动刷新。

我想在每次显示视图控制器时刷新它。

使用我的代码我每次都必须按下刷新按钮，这只是废话。

以下是代码：我该怎么做？

- (IBAction)refresh:(id)sender
{
    NSLog(@"Showing Refresh HUD");
    refreshHUD = [[MBProgressHUD alloc] initWithView:self.view];
    [self.view addSubview:refreshHUD];

    // Register for HUD callbacks so we can remove it from the window at the right time
    refreshHUD.delegate = self;

    // Show the HUD while the provided method executes in a new thread
    [refreshHUD show:YES];

    PFQuery *query = [PFQuery queryWithClassName:@"TPhoto"];
    PFUser *user = [PFUser currentUser];
    [query whereKey:@"user" equalTo:user];
    [query orderByAscending:@"createdAt"];

    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (!error) {
            // The find succeeded.
            if (refreshHUD) {
                [refreshHUD hide:YES];

                refreshHUD = [[MBProgressHUD alloc] initWithView:self.view];
                [self.view addSubview:refreshHUD];

                // The sample image is based on the work by http://www.pixelpressicons.com, http://creativecommons.org/licenses/by/2.5/ca/
                // Make the customViews 37 by 37 pixels for best results (those are the bounds of the build-in progress indicators)
                refreshHUD.customView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"37x-Checkmark.png"]];

                // Set custom view mode
                refreshHUD.mode = MBProgressHUDModeCustomView;

                refreshHUD.delegate = self;
            }
            NSLog(@"Successfully retrieved %d photos.", objects.count);

            // Retrieve existing objectIDs

            NSMutableArray *oldCompareObjectIDArray = [NSMutableArray array];
            for (UIView *view in [photoScrollView subviews]) {
                if ([view isKindOfClass:[UIButton class]]) {
                    UIButton *eachButton = (UIButton *)view;
                    [oldCompareObjectIDArray addObject:[eachButton titleForState:UIControlStateReserved]];
                }
            }

            NSMutableArray *oldCompareObjectIDArray2 = [NSMutableArray arrayWithArray:oldCompareObjectIDArray];

            // If there are photos, we start extracting the data
            // Save a list of object IDs while extracting this data

            NSMutableArray *newObjectIDArray = [NSMutableArray array];
            if (objects.count > 0) {
                for (PFObject *eachObject in objects) {
                    [newObjectIDArray addObject:[eachObject objectId]];
                }
            }

            // Compare the old and new object IDs
            NSMutableArray *newCompareObjectIDArray = [NSMutableArray arrayWithArray:newObjectIDArray];
            NSMutableArray *newCompareObjectIDArray2 = [NSMutableArray arrayWithArray:newObjectIDArray];
            if (oldCompareObjectIDArray.count > 0) {
                // New objects
                [newCompareObjectIDArray removeObjectsInArray:oldCompareObjectIDArray];
                // Remove old objects if you delete them using the web browser
                [oldCompareObjectIDArray removeObjectsInArray:newCompareObjectIDArray2];
                if (oldCompareObjectIDArray.count > 0) {
                    // Check the position in the objectIDArray and remove
                    NSMutableArray *listOfToRemove = [[NSMutableArray alloc] init];
                    for (NSString *objectID in oldCompareObjectIDArray){
                        int i = 0;
                        for (NSString *oldObjectID in oldCompareObjectIDArray2){
                            if ([objectID isEqualToString:oldObjectID]) {
                                // Make list of all that you want to remove and remove at the end
                                [listOfToRemove addObject:[NSNumber numberWithInt:i]];
                            }
                            i++;
                        }
                    }

                    // Remove from the back
                    NSSortDescriptor *highestToLowest = [NSSortDescriptor sortDescriptorWithKey:@"self" ascending:NO];
                    [listOfToRemove sortUsingDescriptors:[NSArray arrayWithObject:highestToLowest]];

                    for (NSNumber *index in listOfToRemove){
                        [allImages removeObjectAtIndex:[index intValue]];
                    }
                }
            }

            // Add new objects
            for (NSString *objectID in newCompareObjectIDArray){
                for (PFObject *eachObject in objects){
                    if ([[eachObject objectId] isEqualToString:objectID]) {
                        NSMutableArray *selectedPhotoArray = [[NSMutableArray alloc] init];
                        [selectedPhotoArray addObject:eachObject];

                        if (selectedPhotoArray.count > 0) {
                            [allImages addObjectsFromArray:selectedPhotoArray];
                        }
                    }
                }
            }

            // Remove and add from objects before this
            [self setUpImages:allImages];

        } else {
            [refreshHUD hide:YES];

            // Log details of the failure
            NSLog(@"Error: %@ %@", error, [error userInfo]);
        }
    }];
}

Answer 1

从视图控制器中的viewDidAppear调用refresh方法。

但是，如果这种情况经常发生，您应该考虑将图像保存在本地缓存中，并且只有在服务器上显示新内容时才刷新它们。

使用解析自动刷新图像

1 个答案: