I have a page for users in a grid view and would like to paginate the view to reduce bandwidth when a user scrolls. For now i know how to paginate a feed view but cannot for a user grid view. Below is my code and what i am trying to achieve.
This is the code i use to paginate a feed view:
func fetchUserPosts() {
let query = Firestore.firestore().collection("posts").limit(to: 15).order(by: "timestamp", descending: true)
if let last = lastDoc {
let next = query.start(afterDocument: last)
next.getDocuments { snapshot, _ in
guard let documents = snapshot?.documents, !documents.isEmpty else { return }
self.lastDoc = snapshot?.documents.last
self.posts.append(contentsOf: documents.compactMap({ try? $0.data(as: Post.self) }))
}
} else {
query.getDocuments { snapshot, _ in
guard let documents = snapshot?.documents else { return }
self.posts = documents.compactMap({ try? $0.data(as: Post.self) })
self.lastDoc = snapshot?.documents.last
}
}
}
I am trying to achieve the same for a usergrid view, below is how far i have gone with errors i have encountered. Any help is appreciated.
class PeopleViewModel: ObservableObject {
#Published var users = [User]()
func fetchAllUsers() {
let query = Firestore.firestore().collection("users").limit(to: 20).order(by: "id", descending: true)
if let last = lastDoc {
let next = query.start(afterDocument: last)
next.getDocuments { snapshot, _ in
guard let documents = snapshot?.documents, !documents.isEmpty else { return }
self.lastDoc = snapshot?.documents.last
self.users //Property is accessed but result is unused
}
} else {
query.getDocuments { snapshot, _ in
guard let documents = snapshot?.documents else { return }
self.users //Property is accessed but result is unused
self.lastDoc = snapshot?.documents.last
}
}
}
}
I am trying to transition an app from UIKit to SwiftUI which depends on basic DynamoDB resources but I have hit a snag in forcing the view to refresh as data is added to the list. I have been at this set of code for hours trying different things and I thought I might see if anyone might know why the 'SessionsData' seems to be thrown away and will not accumulate the 'Sessions' objects.
Does anyone have any quick thoughts???
class SessionsData: ObservableObject {
let didChange = PassthroughSubject<SessionsData, Never>()
#Published var data: [Sessions] = [] {
didSet {
didChange.send(self)
}
}
init() {
load()
}
func load() {
let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
let scanExpression = AWSDynamoDBScanExpression()
scanExpression.limit = 20
var temp : [Sessions] = []
dynamoDBObjectMapper.scan(Sessions.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
if let error = task.error as NSError? {
print("The request failed. Error: \(error)")
} else if let paginatedOutput = task.result {
for session in paginatedOutput.items as! [Sessions] {
print("Item Found")
temp.append(session)
}
DispatchQueue.main.async {
self.data = temp
self.didChange.send(self)
}
}
print(self.data.count)
return true
})
}
}
struct Events: View {
#ObservedObject var sessionsData = SessionsData()
var body: some View {...}
}
Looks like you've over-complicated the code. The PassthroughSubject is unnecessary. Whenever you change a #Published property, it should trigger an update.
class SessionsData: ObservableObject {
#Published var data: [Sessions] = []
init() {
load()
}
func load() {
let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
let scanExpression = AWSDynamoDBScanExpression()
scanExpression.limit = 20
var temp : [Sessions] = []
dynamoDBObjectMapper.scan(Sessions.self, expression: scanExpression).continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
if let error = task.error as NSError? {
print("The request failed. Error: \(error)")
} else if let paginatedOutput = task.result {
for session in paginatedOutput.items as! [Sessions] {
print("Item Found")
temp.append(session)
}
DispatchQueue.main.async {
self.data = temp
}
}
print(self.data.count)
return true
})
}
}
I don't have experience with DynamoDB, but here are a few things from SwiftUI / Combine perspective. In ObseravbleObjects have change a significant bit and and are now declared with objectWillChange and then sending newValue in willSet:
class SessionsData: ObservableObject {
public let objectWillChange = PassthroughSubject<[Sessions], Never>()
public private(set) var items: [Sessions] = [] {
willSet {
objectWillChange.send(newValue)
}
}
init() {
self.items = []
}
public func load() {
let dynamoDBObjectMapper = AWSDynamoDBObjectMapper.default()
let scanExpression = AWSDynamoDBScanExpression()
scanExpression.limit = 20
var temp: [Sessions] = []
dynamoDBObjectMapper
.scan(Sessions.self,
expression: scanExpression)
.continueWith(block: { (task:AWSTask<AWSDynamoDBPaginatedOutput>!) -> Any? in
if let error = task.error as NSError? {
print("The request failed. Error: \(error)")
} else if let paginatedOutput = task.result,
let sessions = paginatedOutput.items as? [Sessions] {
temp.append(contentsOf: sessions)
}
DispatchQueue.main.async {
self.items = temp
}
}
return true
})
}
}
For the UI part you have to just call your load() method defined above in .onApear() and everything else should happen magically:
struct Events: View {
#ObservedObject var sessionsData: SessionsData
var body: some View {
List {
ForEach(self.sessionsData.items) { session in
Text(session.name) // or something of that kind
}
} .onAppear(perform: { self.sessionsData.load() })
}
}
I am working wth a data structure, and I am looping through a couple nodes and here is the json data I get.
Snap (20171012) {
"-KwM45HyW4UduQgKTGn6" = {
ImageName = "Screen Shot 2017-10-13 at 11.24.51 AM.png";
fileURL = "";
thumbFileUrl = "";
user = "User not defined";
};
"-KwM4limD2aRyHgeKE5P" = {
ImageName = "test.png";
fileURL = "";
thumbFileUrl = "";
user = "User not defined";
};
}
After this, I can access the "snap" value using my data.key to get the "20171012"
ref.child(myselected_spot!).observe(DataEventType.value, with: { (snapshot) in
if snapshot.childrenCount > 0 {
for mydata in snapshot.children.allObjects as! [DataSnapshot]
{
if mydata.key.characters.count == 8 {
self.formattedDates.append(convertDate(stringDate: mydata.key))
self.selected_dates.append(mydata.key)
How would I get the value for "ImageName"
Your mydata is another DataSnapshot, so you can access all methods and properties of that class. In this case you're looking for DataSnapshot.childSnapshotForPath::
ref.child(myselected_spot!).observe(DataEventType.value, with: { (snapshot) in if snapshot.childrenCount > 0 {
for mydata in snapshot.children.allObjects as! [DataSnapshot]
{
if mydata.key.characters.count == 8 {
self.formattedDates.append(convertDate(stringDate: mydata.key))
self.selected_dates.append(mydata.key)
print(mydata.childSnapshot(forPath: "ImageName").value)
Pretty simple - I do not know what the variable myselected_Spot is but I am going to assume it's -KwM45HyW4UduQgKTGn6. If the below code does not yield results - I will need to know what that variable is.
ref.child(myselectd_spot).observe(.value, with: { (snapshot) in
if snapshot.value is NSNull{
//handles errors
return
}
else{
if let selectedSnapDict = snapshot.value as? NSDictionary {//Can also be [String: Any]
print(selectedSnapDict["ImageName"] as! String) //We know it's a string
}
else{
//null
}
}
})
I have created a function for mapping json data to a sqlite store using sqlite.swift. I am receiving strange behavior though since the first time I try to run an insert I get a "No such table" error". But the inserts work perfectly after that initial throw. My code works by making a connection to the database onload using SQLData.instance.connect(). Then every time a call to insert is placed it initializes the table to make sure it is set up with all the columns within the data.
//attached to button
let userJSON = JSON(["user_id" : id, "username" : email])
SQLData.instance.insert(table: "users", data: userJSON) { result in
if let result = result{
print(result)
}
}
//sql class
class SQLData {
static let instance = SQLData()
var db: Connection? = nil
func connect() {
let path = NSSearchPathForDirectoriesInDomains(
.documentDirectory, .userDomainMask, true
).first!
do {
self.db = try Connection("\(path)/contacts.sqlite3")
if let db = self.db {
try db.run(Table("users").drop(ifExists: true))
}
print("SQLite connection established.")
} catch {
print("Couldn't create SQLite connection.")
}
}
func initTable(table: String, data: JSON, completionHandler: (Table?) -> Void){
if let db = db {
let t = Table(table)
do {
try db.run(t.create(temporary: false, ifNotExists: true) { r in
r.column(Expression<Int>("id"), primaryKey: true)
r.column(Expression<Bool>("synced"), defaultValue: false)
for (key,val) in data {
if val.bool != nil{
r.column(Expression<Bool>(key), defaultValue: false)
} else if val.int != nil {
r.column(Expression<Int>(key), defaultValue: 0)
} else if val.double != nil {
r.column(Expression<Double>(key), defaultValue: 0.0)
} else {
r.column(Expression<String?>(key), defaultValue: "")
}
}
completionHandler(t)
})
} catch let err {
print(err)
completionHandler(nil)
}
} else {
completionHandler(nil)
}
}
func insert(table: String, data: JSON, completionHandler: #escaping (Int64?) -> Void){
self.initTable(table: table, data: data) { t in
if let db = db, let t = t {
var query: [Setter] = []
for (key, val) in data {
if val.bool != nil{
query.append(Expression<Bool>(key) <- val.boolValue)
} else if val.int != nil {
query.append(Expression<Int>(key) <- val.intValue)
} else if val.double != nil {
query.append(Expression<Double>(key) <- val.doubleValue)
} else {
query.append(Expression<String?>(key) <- val.stringValue)
}
}
do {
try db.transaction {
let insert = t.insert(query)
let rowid = try db.run(insert)
completionHandler(rowid)
}
} catch let err {
print(err)
completionHandler(nil)
}
} else {
completionHandler(nil)
}
}
}
}
Change your connection function as below
func connect(){
do {
let databaseFilePath = Bundle.main.path(forResource: "contacts", ofType: "sqlite3")!
db = try Connection(databaseFilePath)
} catch {
print(error)
}
}
and bu sure your .sqlite3 (or .db) file in to your project hierarchy and copy bundle resources like images
I'm struggling with this Swift code already for some time and do not find the problem. The code
below should provide the File Directory as DataSource for a NSOutlineView. The GUI is quite simple
just a window with a NSOutlineView and a Object for the OutlineViewController instance.
When I start the application it shows the root entry, when I expand the root entry it shows for a short period the sub items. Then the application crashes with an Error in file "main.swift" at line "NSApplicationMain(C_ARGC, C_ARGV) --> "EXC_BAD_ACCESS(code=EXC_I386_GPFLT)" ?
If added some println() to proof the directory structure - this seems to be fine.
The swift code:
import Cocoa
import Foundation
class FileSystemItem {
let propertyKeys = [NSURLLocalizedNameKey, NSURLEffectiveIconKey, NSURLIsPackageKey, NSURLIsDirectoryKey,NSURLTypeIdentifierKey]
let fileURL: NSURL
var name: String! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLNameKey], error: nil)
return resourceValues[NSURLNameKey] as? NSString
}
var localizedName: String! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLLocalizedNameKey], error: nil)
return resourceValues[NSURLLocalizedNameKey] as? NSString
}
var icon: NSImage! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLEffectiveIconKey], error: nil)
return resourceValues[NSURLEffectiveIconKey] as? NSImage
}
var dateOfCreation: NSDate! {
let resourceValues = self.fileURL.resourceValuesForKeys([NSURLCreationDateKey], error: nil)
return resourceValues[NSURLCreationDateKey] as? NSDate
}
var dateOfLastModification: NSDate! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLContentModificationDateKey], error: nil)
return resourceValues[NSURLContentModificationDateKey] as? NSDate
}
var typeIdentifier: String! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLTypeIdentifierKey], error: nil)
return resourceValues[NSURLTypeIdentifierKey] as? NSString
}
var isDirectory: String! {
let resourceValues = fileURL.resourceValuesForKeys([NSURLIsDirectoryKey], error: nil)
return resourceValues[NSURLIsDirectoryKey] as? NSString
}
var children: [FileSystemItem] {
var childs: [FileSystemItem] = []
var isDirectory: ObjCBool = ObjCBool(1)
let fileManager = NSFileManager.defaultManager()
var checkValidation = NSFileManager.defaultManager()
if (checkValidation.fileExistsAtPath(fileURL.relativePath)) {
if let itemURLs = fileManager.contentsOfDirectoryAtURL(fileURL, includingPropertiesForKeys:propertyKeys, options:.SkipsHiddenFiles, error:nil) {
for fsItemURL in itemURLs as [NSURL] {
if (fileManager.fileExistsAtPath(fsItemURL.relativePath, isDirectory: &isDirectory))
{
if(isDirectory == true) {
let checkItem = FileSystemItem(fileURL: fsItemURL)
childs.append(checkItem)
}
}
}
}
}
return childs
}
init (fileURL: NSURL) {
self.fileURL = fileURL
}
func hasChildren() -> Bool {
return self.children.count > 0
}
}
class OutlineViewController : NSObject, NSOutlineViewDataSource {
let rootFolder : String = "/"
let rootfsItem : FileSystemItem
let fsItemURL : NSURL
let propertyKeys = [NSURLLocalizedNameKey, NSURLEffectiveIconKey, NSURLIsPackageKey, NSURLIsDirectoryKey,NSURLTypeIdentifierKey]
init() {
self.fsItemURL = NSURL.fileURLWithPath(rootFolder)
self.rootfsItem = FileSystemItem(fileURL: fsItemURL)
for fsItem in rootfsItem.children as [FileSystemItem] {
for fsSubItem in fsItem.children as [FileSystemItem] {
println("\(fsItem.name) - \(fsSubItem.name)")
}
}
}
func outlineView(outlineView: NSOutlineView!, numberOfChildrenOfItem item: AnyObject!) -> Int {
if let theItem: AnyObject = item {
let tmpfsItem: FileSystemItem = item as FileSystemItem
return tmpfsItem.children.count
}
return 1
}
func outlineView(outlineView: NSOutlineView!, isItemExpandable item: AnyObject!) -> Bool {
if let theItem: AnyObject = item {
let tmpfsItem: FileSystemItem = item as FileSystemItem
return tmpfsItem.hasChildren()
}
return false
}
func outlineView(outlineView: NSOutlineView!, child index: Int, ofItem item: AnyObject!) -> AnyObject! {
if let theItem: AnyObject = item {
let tmpfsItem: FileSystemItem = item as FileSystemItem
return tmpfsItem.children[index]
}
return rootfsItem
}
func outlineView(outlineView: NSOutlineView!, objectValueForTableColumn tableColumn: NSTableColumn!, byItem item: AnyObject!) -> AnyObject! {
if let theItem: AnyObject = item {
let tmpfsItem: FileSystemItem = item as FileSystemItem
return tmpfsItem.localizedName
}
return "-empty-"
}
}
class AppDelegate: NSObject, NSApplicationDelegate {
#IBOutlet var window: NSWindow
func applicationDidFinishLaunching(aNotification: NSNotification?) {
// Insert code here to initialize your application
}
func applicationWillTerminate(aNotification: NSNotification?) {
// Insert code here to tear down your application
}
}
Any hints ?
I had a similar problem with EXC_BAD_ACCESS on an NSOutlineView - with an NSOutlineViewDataSource. The same behaviour of as soon as the node was expanded, the data was displayed then the crash occurred. Some profiling in instruments showed that somewhere a Zombie object was created, and then the Outline view tried to access it.
I think this is a bug - but I managed to get around it by changing all Swift 'Strings' to 'NSStrings'. This may have to be done for all Swift types if you are using them.
In order to ensure everything was an NSString, I had to declare constants within the class such as:
var empty_string : NSString = ""
Because anytime I fed it a Swift string all hell broke loose. Oh well hopefully this will be fixed in the future!
So, just to clarify what is going on. NSOutlineView does not retain objects that it is given for its "model"; it was always expected that the client would retain them. For ARC code, this doesn't work well, because if you return a new instance to the NSOutlineView methods the object will not be retained by anything and will quickly be freed. Then subsequent outlineView delegate methods the touch these objects will lead to crashes. The solution to that is to retain the objects yourself in your own array.
Note that the objects returned from objectValueForTableColumn are retained by the NSControl's objectValue.
Back to Swift: As Thomas noted the objects have to be objc objects since they are bridged to an objc class. A Swift string is implicitly bridged to a temporary NSString. This leads to a crash because of the above issue, since nothing retains the NSString instance. That is why maintaining an array of NSStrings "solves" this problem.
The solution would be for NSOutlineView to have an option to retain the items given to it. Please consider logging a bug request for it to do this through bugreporter.apple.com
Thanks,
corbin (I work on NSOutlineView)
It seems that
outlineView(outlineView: NSOutlineView!, objectValueForTableColumn tableColumn: NSTableColumn!, byItem item: AnyObject!) -> AnyObject!
needs to return an object that conforms to obj-c protocol. So you can return
#objc class MyClass {
...
}
(or NSString and the like). But not native Swift stuff like String or Array etc.
I believe one of the problems going on here is the fact that the "children" array is getting replaced every time the children property is accessed.
I think this causes some weak references inside the NSOutlineView to break when it queries the DataSource for information.
If you cache the "children" and access the cache to compute "numberOfChildren" and "getChildForIndex" you should see an improvement.
In Swift 3.0 I used the following code, which compiles and runs without problems. It is far away from being complete but a step in the right direction, since I am trying to translate TreeTest into Swift.
import Cocoa
import Foundation
class FileSystemItem: NSObject {
let propertyKeys: [URLResourceKey] = [.localizedNameKey, .effectiveIconKey, .isDirectoryKey, .typeIdentifierKey]
var fileURL: URL
var name: String! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.nameKey])
return resourceValues.name
}
var localizedName: String! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.localizedNameKey])
return resourceValues.localizedName
}
var icon: NSImage! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.effectiveIconKey])
return resourceValues.effectiveIcon as? NSImage
}
var dateOfCreation: Date! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.creationDateKey])
return resourceValues.creationDate
}
var dateOfLastModification: Date! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.contentModificationDateKey])
return resourceValues.contentAccessDate
}
var typeIdentifier: String! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.typeIdentifierKey])
return resourceValues.typeIdentifier
}
var isDirectory: Bool! {
let resourceValues = try! fileURL.resourceValues(forKeys: [.isDirectoryKey])
return resourceValues.isDirectory
}
init(url: Foundation.URL) {
self.fileURL = url
}
var children: [FileSystemItem] {
var childs: [FileSystemItem] = []
let fileManager = FileManager.default
// show no hidden Files (if you want this, comment out next line)
// let options = FileManager.DirectoryEnumerationOptions.skipsHiddenFiles
var directoryURL = ObjCBool(false)
let validURL = fileManager.fileExists(atPath: fileURL.relativePath, isDirectory: &directoryURL)
if (validURL && directoryURL.boolValue) {
// contents of directory
do {
let childURLs = try
fileManager.contentsOfDirectory(at: fileURL, includingPropertiesForKeys: propertyKeys, options: [])
for childURL in childURLs {
let child = FileSystemItem(url: childURL)
childs.append(child)
}
}
catch {
print("Unexpected error occured: \(error).")
}
}
return childs
}
func hasChildren() -> Bool {
return self.children.count > 0
}
}
class OutLineViewController: NSViewController, NSOutlineViewDelegate, NSOutlineViewDataSource {
#IBOutlet weak var outlineView: NSOutlineView!
#IBOutlet weak var pathController: NSPathControl!
var fileSystemItemURL: URL!
let propertyKeys: [URLResourceKey] = [.localizedNameKey, .effectiveIconKey, .isDirectoryKey, .typeIdentifierKey]
var rootfileSystemItem: FileSystemItem!
var rootURL: URL!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
let userDirectoryURL = URL(fileURLWithPath: NSHomeDirectory())
// directory "Pictures" is set as root
let rootURL = userDirectoryURL.appendingPathComponent("Pictures", isDirectory: true)
self.pathController.url = rootURL
self.rootfileSystemItem = FileSystemItem(url: rootURL)
for fileSystemItem in rootfileSystemItem.children as [FileSystemItem] {
for subItem in fileSystemItem.children as [FileSystemItem] {
print("\(fileSystemItem.name) - \(subItem.name)")
}
}
//FileSystemItem.rootItemWithPath(self.pathControl.URL.path)
//self.searchForFilesInDirectory(picturesPath)
}
override var representedObject: Any? {
didSet {
// Update the view, if already loaded.
}
}
#IBAction func pathControllerAction(_ sender: NSPathControl) {
print("controller clicked")
}
// MARK: - outline data source methods
func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.children.count
}
return 1
}
func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.hasChildren()
}
return false
}
func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.children[index]
}
return rootfileSystemItem
}
func outlineView(_ outlineView: NSOutlineView, objectValueFor tableColumn: NSTableColumn?, byItem item: Any?) -> Any? {
if let fileSystemItem = item as? FileSystemItem {
switch tableColumn?.identifier {
case "tree"?:
return fileSystemItem.localizedName
case "coordinate"?:
return " empty "
default:
break
}
}
return " -empty- "
}
// MARK: - outline view delegate methods
func outlineView(_ outlineView: NSOutlineView, shouldEdit tableColumn: NSTableColumn?, item: Any) -> Bool {
return false
}
}
With a new edit the outline view now shows all files and directories. You can influence the appearance in the children section in class FileSystemItem.