Fix/reload data animation glitch fix

Example/LongListViewController.swift

@@ -23,9 +23,21 @@
 import UIKit
 import SwiftReorder
 
+private extension String {
+
+    /// Generates random string with spaces.
+    static func random(length: Int, averageWordLength: Int? = nil) -> String {
+        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+        let spacesCount = averageWordLength == nil ? 0 : letters.count / averageWordLength!
+        let lettersWithSpace = letters.appending(String(repeating: " ", count: spacesCount))
+        return String((0..<length).map{ _ in lettersWithSpace.randomElement()! })
+    }
+}
+
+
 class LongListViewController: UITableViewController {
 
-    var items = (1...50).map { "Item \($0)" }
+    var items = (1...10000).map { _ in String.random(length: Int.random(in: 0...200), averageWordLength: 5) }
 
     required init?(coder aDecoder: NSCoder) {
         fatalError("init(coder:) has not been implemented")
@@ -41,6 +53,8 @@ class LongListViewController: UITableViewController {
         title = "Long List"
 
         tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell")
+        tableView.estimatedRowHeight = 44
+        tableView.rowHeight = UITableView.automaticDimension
         tableView.allowsSelection = false
         tableView.reorder.delegate = self
     }
@@ -60,6 +74,7 @@ extension LongListViewController {
 
         let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
         cell.textLabel?.text = items[indexPath.row]
+        cell.textLabel?.numberOfLines = 0
 
         return cell
     }

Source/ReorderController+DestinationRow.swift

@@ -46,10 +46,7 @@ extension ReorderController {
 
         delegate?.tableView(tableView, reorderRowAt: context.destinationRow, to: newContext.destinationRow)
 
-        tableView.beginUpdates()
-        tableView.deleteRows(at: [context.destinationRow], with: .fade)
-        tableView.insertRows(at: [newContext.destinationRow], with: .fade)
-        tableView.endUpdates()
+        tableView.moveRow(at: context.destinationRow, to: newContext.destinationRow)
     }
 
     func proposedNewDestinationRow() -> IndexPath? {

Source/ReorderController+SnapshotView.swift

@@ -28,7 +28,6 @@ extension ReorderController {
         guard let tableView = tableView, let superview = tableView.superview else { return }
 
         removeSnapshotView()
-        tableView.reloadRows(at: [indexPath], with: .none)
 
         guard let cell = tableView.cellForRow(at: indexPath) else { return }
         let cellFrame = tableView.convert(cell.frame, to: superview)

Source/ReorderController.swift

@@ -183,14 +183,14 @@ public class ReorderController: NSObject {
 
     // MARK: - Internal state
 
-    struct ReorderContext {
+    struct ReorderContext: Equatable {
         var sourceRow: IndexPath
         var destinationRow: IndexPath
         var snapshotOffset: CGFloat
         var touchPosition: CGPoint
     }
 
-    enum ReorderState {
+    enum ReorderState: Equatable {
         case ready(snapshotRow: IndexPath?)
         case reordering(context: ReorderContext)
     }
@@ -233,14 +233,25 @@ public class ReorderController: NSObject {
         let tableTouchPosition = superview.convert(touchPosition, to: tableView)
 
         guard let sourceRow = tableView.indexPathForRow(at: tableTouchPosition),
+            let sourceCell = tableView.cellForRow(at: sourceRow),
             delegate.tableView(tableView, canReorderRowAt: sourceRow)
         else { return }
 
         createSnapshotViewForCell(at: sourceRow)
         animateSnapshotViewIn()
         activateAutoScrollDisplayLink()
 
-        tableView.reloadData()
+        reorderState = .ready(snapshotRow: sourceRow)
+        tableView.reloadRows(at: [sourceRow], with: .none)
+
+        // So after I started to use `reloadRows` instead of `reloadData` I faced with
+        // strange animation glitches that was caused by too damn smart UITableView
+        // wasn't removing previous cell while I was dragging during `animateSnapshotViewIn`
+        // animation. Not easy to reproduce though because need a good timing when you already dragging
+        // and recognizer decides that it's a good time to begin. Anyway, was able to fix it with removing
+        // previous cell manually. Ah yes I switched to `reloadRows` to fix cells reordering when there are like
+        // thousands of cells.
+        sourceCell.removeFromSuperview()
 
         let snapshotOffset = (snapshotView?.center.y ?? 0) - touchPosition.y
 
@@ -312,15 +323,19 @@ public class ReorderController: NSObject {
         let cell = UITableViewCell()
         let height = snapshotView.bounds.height
 
-        NSLayoutConstraint(
-            item: cell,
+        let constraint = NSLayoutConstraint(
+            item: cell.contentView,
             attribute: .height,
             relatedBy: .equal,
             toItem: nil,
             attribute: .notAnAttribute,
             multiplier: 0,
             constant: height
-        ).isActive = true
+        )
+
+        // Prevent broken constraints
+        constraint.priority = .init(999)
+        constraint.isActive = true
 
         let hideCell: Bool
         switch spacerCellStyle {