我無法從Sqlite資料庫中獲取資料

我無法從 Sqlite 資料庫中獲取資料。它不會為我列印任何東西。我檢查了與資料庫的連接，并且資料庫包含資料。它沒有給出錯誤，但不列印任何內容。當我啟動應用程式時，tableView 不包含任何記錄。

在控制臺列印這個：

在 [d24547a13b] 的第 139466 行使用 NULL 資料庫連接指標濫用 API 呼叫
準備：記憶體不足

// AppDelegate.swift

import UIKit
import SQLite3

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        
DataManager.dataManager.dbOpaquePointer = DataManager.dataManager.openDatabase(dbName: "DB.sqlite")
        
return true

}

}

// TableWord.swift

import Foundation

class TableWord{

    var idword: Int = 0
    var word: String = ""
    var features: String = ""
    var number: Int = 0
    
    init(idword: Int, word: String, features: String, number: Int) {
        self.idword = idword
        self.word = word
        self.features = features
        self.number = number
    }
    
}

// DataManager.swift

import UIKit
import SQLite3


class DataManager {
    
    static let dataManager = DataManager()

    var dbOpaquePointer: OpaquePointer?
    
    // OPEN
    func openDatabase(dbName: String) -> OpaquePointer? {
        

        let documentDirectory = try? FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
        let fileUrl = documentDirectory?.appendingPathComponent(dbName).relativePath
        
        
        guard let part1DbPath = fileUrl else {
            print("part1DbPath is nil.")
            return nil
        }
        

        if sqlite3_open(part1DbPath, &dbOpaquePointer) == SQLITE_OK {
            print(“Open database in \(part1DbPath)")
            return dbOpaquePointer
        } else {
            print("\(Errors.SQLiteError.openDatabase)")
        }
        
        return dbOpaquePointer
        
    }
    
    
    
    // SELECT
    func selectTableWord() -> [TableWord] {
        
        let querySelectTableWord = "SELECT * FROM tableword;"
        
        var dbOpaquePointer2: OpaquePointer? = nil
        
        var dataTableWord: [TableWord] = []
        
        if sqlite3_prepare_v2(dbOpaquePointer, querySelectTableWord, -1, &dbOpaquePointer2, nil) == SQLITE_OK {
            
            while (sqlite3_step(dbOpaquePointer2) == SQLITE_ROW) {
                
                let idword = sqlite3_column_int(dbOpaquePointer2, 0)
                
                guard let queryResultCol1 = sqlite3_column_text(dbOpaquePointer2, 1) else {
                    print("\(Errors.SQLiteError.queryNil)")
                    return dataTableWord
                }
                
                let word = String(cString: queryResultCol1)
                
                guard let queryResultCol2 = sqlite3_column_text(dbOpaquePointer2, 2) else {
                    print("\(Errors.SQLiteError.queryNil)")
                    return dataTableWord
                }
                
                let features = String(cString: queryResultCol2)
                
                let number = sqlite3_column_int(dbOpaquePointer2, 3)
                
                dataTableWord.append(TableWord(idword: Int(idword), word: word, features: features, number: Int(number)))
                
            }
            
            
        } else {
            let errorMessage = String(cString: sqlite3_errmsg(dbOpaquePointer2))
            print("\(Errors.SQLiteError.prepare): \(errorMessage)")
        }
        
        sqlite3_finalize(dbOpaquePointer2)
        
        return dataTableWord
        
    }
    
    
}

// ViewController.swift

import UIKit
import SQLite3

class ViewController: UIViewController, UITextViewDelegate, UITableViewDataSource {
    
    @IBOutlet weak var resultTableView: UITableView!
    
    var db: DataManager = DataManager()
    
    var dataTableWord: [TableWord] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        dataTableWord = db.selectTableWord()
        
        searchTextView.delegate = self
        resultTableView.dataSource = self
        
    }

    //MARK: - UITableViewDataSource

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dataTableWord.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "idCell1Main1", for: indexPath) as! TableViewCell
        
       cell.cellLabelNumber.text = String(dataTableWord[indexPath.row].idword)
       cell.cellLabelTitle.text = dataTableWord[indexPath.row].word
       cell.cellLabelSubtitle.text = dataTableWord[indexPath.row].features

    return cell

    }

}

uj5u.com熱心網友回復：

在 viewDidLoad 你打電話

var db: DataManager = DataManager()

這意味著您正在創建一個新的 DataManager 實體，而不是使用您在應用程式委托中創建并且具有開放資料庫連接的實體

您應該始終使用您創建的靜態屬性訪問您的資料庫

let db = DataManager.databaseManager

為了避免這樣的錯誤，你可以在你的類中添加一個私有初始化

private init() {}

這樣你只能通過 DataManager.databaseManager

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