• Uitableview diffable data source

    Uitableview diffable data source

    Diffable Data Sources come with a few benefits over using the classic data source approach and are the preferred way nowadays to work with collection- and table views. However, it might not always be easy to rewrite existing code which is heavily integrated into using the old approach.

    This is too bad as it takes away the opportunity to benefit from this great new API. An example of construction could look as follows:.

    The data source is generic and defines a type for section identifiers and a type for the data that is listed. The cell provider will take this generic as output for the third argument containing the data for which a cell needs to be returned. Data is provided through so-called snapshots: a snapshot of data.

    This already describes how diffable data sources work. Snapshots of data are compared with each other to determine the minimum amount of changes needed to go from one snapshot to another.

    The data source is smart enough to calculate the differences and replaces code like performBatchUpdatesfor example. Diffable Data Sources result in code that is more compact and centralized while at the same time bringing several benefits. In the end, the system takes over a lot of the heavy lifting. Invalid update: invalid number of items in section 0.

    The number of items contained in an existing section after the update 1 must be equal to the number of items contained in that section before the update 1plus or minus the number of items inserted or deleted from that section 1 inserted, 0 deleted and plus or minus the number of items moved into or out of that section 0 moved in, 0 moved out. Diffable Data Sources aims to take away this error completely by taking over the responsibility to calculate changes between snapshots.

    Another place in which diffable data sources really shine is the delegate of an NSFetchedResultsController. We would iterate over each NSFetchedResultsChangeType to make sure we perform all those changes using the correct collection- or table view method.

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    Each update is executed inside a performBatchUpdates and we cross our fingers to hope for the best result possible. This is another point in which the earlier mentioned error could occur. Luckily enough, we can now adopt one of the methods that replace all this logic inside the NSFetchedResultsControllerDelegate :. But how about migrating old code? I promised you a simple extension that simplifies the migration to diffable data sources. The code reuses the existing data source methods to provide cell configurations.Hey guys.

    I am trying to work out how to add headers to my sections in my uitableview. I have seen a post from here about that and the guy had a solutions. But it doesnt work for me tho. I have created an enum for sections:. It's my third month into programming so I am gonna be honest. I would highly appriciate some slow explanation what am I doing wrong and what could I do better. Let me explain the app exactly. It's a simple Note app. UITableView has two sections. By filling the textField and clicking an actionButton, program creates a cell with that string and update the first section of the table view.

    Before creating viewForHeaderInSection everyhting worked just fine. Now it does not. I would like to know how to create two headers with the two different names for the section1 and section2.

    Many thanks for any help and your own time. I think you are missing the code to register the header class with the TableView. Without the registration TableViews does. Hey Filip. You were right I did miss that in my collectionView configuration. That however did not solve the issue entirely. It seems like the headerViewCell is indeed registered as program proceed and does not crush. However that cell did not appear in my tableView.

    I missed that you have a diffable data source, you need to set the supplementaryViewProvider method on the data source. The method you have is for older collectionView or tableView implementations that dont use diffable. Also I have this open source project on GitHub which shows how to use Diffable with section headers.As good developers, we need to implement the protocol methods and making sure to sync our backing model with the data source properly to avoid any crashes because of inconsistencies between them.

    Also, when we need to perform granular updates for sections and rows in our TableViewwe need to use the API like the sample code below. It's actually pretty hard to make sure all the section and rows are correctly updated for each insert, reload, and deletion based on the value between the old and new data.

    It is called Diffable Data Source. Snapshot acts as a source of truth between our view and data source, whenever there are changes in our model, we just need to construct a new snapshot and applies it to the current snapshot. All the diffing, view update with animation will be performed automagically for us. Also, we don't need to deal with indexPath when we dequeue our cell, the exact model will be given to us to render in the cell based on generic API.

    Advances in UI Data Sources. There is a mandatory requirement that developer must follow to make sure the diffing works correctly. We need to provide sections and item type representation that can provide unique value.

    As we can see the SectionIdentifierType and ItemIdentifierType are generic that we must provide when we declare and initialise the class. We also need to make sure the hashValue are unique for each instance to avoid hash collision. There are several features that we want to build such as:.

    The starter project already provides the resources such as cells, image assets, and JSON stubs file for the cities and places. Here are the essential components from the starter project:. Our section will be represented by the City enum. In this case we have 3 cities: Osaka, Kyoto, and Tokyo.

    The enum underlying raw type will be String. This enum will automatically conforms to Hashable protocol using the rawValue as the unique hashValue.

    Create a new file called City.

    Using Diffable Data Source iOS 13 API in UITableView

    Fill the file using the code below to create the enum for the City. For the row representation, we will create struct called Place. The struct has several underlying properties such as namedescriptionimageName. We also have the UUID as the properties to make sure each of the place instance is unique. Create a new file called Place.

    Fill the file using the code below to create the struct for the Place. Next, we need to make it conform the Hashable protocol. Below the code, create an extension for the Place that implements Hashable. Then, we need to provide the hasher value that will be used to create the hashValue. In this case we combine all the properties of the Place into the hasher. The starter project already provide a helper extension method for the bundle to load the data from a JSON file and decode it using generic method with Decodable type as the placeholder.

    uitableview diffable data source

    Inside the Place. With the constraint, the extension will only be applied to array of Place. In the extension, we just create 3 static computed property that returns array of place for Osaka, Kyoto, and Tokyo using our extension bundle static method. Next, we will associate the stub places for each of the City enum. Go to City. We declare a static computed property with array of tuple containing the city associated with array of places.

    That's it! We now have our model with the stub data as well, let's move on to our ViewController to build our TableView using Diffable Data Source.Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. The uitableviewdiffabledatasource tag has no usage guidance.

    Learn more. Questions tagged [uitableviewdiffabledatasource]. Ask Question. Learn more… Top users Synonyms. Filter by. Sorted by. Tagged with. Apply filter.

    I have been trying to debug it for 2 days now and can't seem to figure out a way to resolve this issue. Vandan Patel 1 1 gold badge 10 10 silver badges 22 22 bronze badges.

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    But my When I'm creating a new snapshot with the same data and apply that snapshot, it results Nonouf 2 2 gold badges 4 4 silver badges 17 17 bronze badges.

    Austin Conlon 8 8 silver badges 20 20 bronze badges. Ahmed Ghrib 1 1 gold badge 11 11 silver badges 20 20 bronze badges. Moritz Schaub 48 6 6 bronze badges. Andy Nadal 66 5 5 bronze badges. I am trying to understand the correct way to handle Replacing all the data - pull to refresh Append new items Teddy K 2 2 silver badges 10 10 bronze badges.

    Harshal Wani 1, 1 1 gold badge 19 19 silver badges 36 36 bronze badges. It's working fine in IOS When I run this application below iOS 13 Version then it gives me warning that it available on ios Yogesh Patel 1, 8 8 silver badges 24 24 bronze badges. Peter Lapisu 18k 14 14 gold badges silver badges bronze badges. The Overflow Blog.

    uitableview diffable data source

    Episode Gaming PCs to heat your home, oceans to cool your data centers. Featured on Meta. Hot Network Questions. Newest uitableviewdiffabledatasource questions feed. Stack Overflow works best with JavaScript enabled.Some incredible advancements have also been made within the existing UI frameworks, such as the new built-in, diffable data sources for table views and collection views — which could potentially eliminate a whole class of very common bugs found in many different apps.

    One such benefit — arguably one of the major ones — is that declarative APIs tend to reduce the opportunity for errors to occur, by reducing statefulness. When an app has less state to keep track of, fewer bugs tend to appear — since the risk of various states ending up out-of-sync is heavily reduced. So this year, Apple is outfitting both of these classes with brand new data source APIs — which come together as a big step forward in terms of developer experience, robustness, and efficiency.

    Along those same lines, the reason we specify our model type — Contact — as the second generic type, is because our data source will use those values to uniquely identify each cell and its corresponding data. No more passing around index paths — and again improving type safety. Second, our model — which contains the name and email address of one of our contacts — and has been made Hashable in order for our diffable data source to be able to uniquely identify it.

    But now, updating our table view is just a matter of constructing a snapshot of its current data, and passing that directly to our data source by calling its apply method. No batch updates, no fiddling around with index paths, none of that stuff! When doing the above, our UITableViewDiffableDataSource will take the snapshot we constructed, diff it — and then update our UI with the resulting changes — all automatically, including calculating the most appropriate animations to use.

    Really cool! Diffable data sources is a huge leap forward in terms of how easy both table views and collection views are to work with — and how stable the implementations we build on top of them are likely to become. By providing a more declarative API that moves much of the complexity of dealing with UI state into UIKit itself, a huge class of mistakes and bugs can be avoided — most likely resulting in fewer crashes, and better-performing apps.

    What do you think?

    Modern table views with diffable data sources

    Let me know on Twitter johnsundell. Brought to you by these wonderful sponsors: BitriseElementsInstabugand Duolingo.Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Apple's sample code 1 has:.

    I wrapped my different data in an enum with associated values. I'd add that you should ensure that your backing associated values are Hashableor else you'll need to implement that.

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    That is what the diff'ing algorithm uses to identify each cell, and resolve movements, etc. The key is to use a more generic type. Swift's AnyHashable works well here.

    And you just need to cast the instance of AnyHashable to a more specific class. Learn more. DiffableDataSource with multiple cell types Ask Question. Asked 1 year, 5 months ago.

    How to use Lazy in Swift

    Active 10 months ago. Viewed 1k times. Am I missing something obvious? Jason Moore Jason Moore 6, 1 1 gold badge 40 40 silver badges 45 45 bronze badges. Active Oldest Votes. You definitely need to have a single data source.

    Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.Published by donnywals on December 21, December 21, These new diffable data source classes allow us to define data sources for collection- and table views in terms of snapshots that represent the current state of the underlying models.

    uitableview diffable data source

    The diffable data source will then compare the new snapshot to the old snapshot and it will automatically apply any insertions, deletions, and reordering of its contents. Since the table view data source is pretty much the same as the collection view version apart from some class names, I will focus only on the table view variant. The following topics are covered in this article:. By the end of this article, you will know exactly how to use diffable data sources and what their caveats are.

    This means that it will supply your table view with the number of sections and items it needs to render, and it supplies your table view with the cells it needs to display.

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    To do all this the diffable data source requires a snapshot of your model data. This snapshot contains the sections and items that are used to render your page. Apple refers to these sections and items as identifiers. The reason for this is that these identifiers must hashable, and the diffable data source uses the hash values for all identifiers to determine what's changed.

    Let's look at this a little bit more in-depth by exploring the type signatures of both the data source and the snapshot. That's quite the mouthful! Both are constrained so that whatever type fills the generic type must conform to Hashable.

    If you're not familiar with generics, check out this post I wrote as an introduction to generics in Swift. But, as the name of the generic suggests that might not be the greatest idea. I will explain why in the best practices section. For now, what matters is that you understand that both identifiers must conform to Hashable and that the data source will use hash values to determine changes in your data set. The snapshot object is a struct rather than a class, and it has the same generic parameters as the diffable data source it's applied to.

    This means that you can't apply a snapshot with a set of identifiers to a data source with different identifiers and your code will fail to compile. Now that you know how a diffable data source is defined, and have a rough idea of how it works, let's get more practical and see how you can use a diffable data source in your apps.

    In this section, I will use a very simple data model where my section identifiers are integers, and my model contains only a title property. In reality, your models will be much complicated than what I'm using here.


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