通过调用datalayer将数据获取到ViewModel中

本文关键字：ViewModel 数据获取 调用 datalayer | 更新日期: 2023-09-27 18:19:26

我试图将存储的数据从SQLite数据库中获取到一个简单的文本框中，但一直为null。当数据层被调用时，数据一开始加载正确，但在某个时候它再次变为空，我不知道它在哪里或为什么出错。

这是我的ViewModel

public class FirstReadViewModel : NotifyUIBase
{    
    private string _scriptNotes;
    public string ScriptNotes    //binded in the View
    {
        get { return _scriptNotes; }
        set { _scriptNotes = value; RaisePropertyChanged("ScriptNotes"); }
    }
    public FirstReadViewModel()
    {
        var dbFunctions = new DataLayer();
        dbFunctions.GetFirstReadNotes();
    } 
}

DataLayer

public void GetFirstReadNotes()
{
    String dbConnectionString = @"Data Source =DB.sqlite";
    SQLiteConnection cnn = new SQLiteConnection(dbConnectionString);
    cnn.Open();
    SQLiteCommand cmd = new SQLiteCommand(cnn);
    cmd.CommandText = "SELECT* FROM projects WHERE projectID = 1";
    SQLiteDataReader reader = cmd.ExecuteReader();
    while (reader.Read())
    {
         string ScriptNotes = reader["scriptnotes"].ToString();
    }
    reader.Close();
    cnn.Close();
    }
}

通过调用datalayer将数据获取到ViewModel中

您的数据层方法应该如下所示，因为您只想返回第一个音符：

public string GetFirstReadNotes()
{
    string scriptNotes = string.Empty;
    String dbConnectionString = @"Data Source =DB.sqlite";
    SQLiteConnection cnn = new SQLiteConnection(dbConnectionString);
    cnn.Open();
    SQLiteCommand cmd = new SQLiteCommand(cnn);
    cmd.CommandText = "SELECT* FROM projects WHERE projectID = 1";
    SQLiteDataReader reader = cmd.ExecuteReader();
    if(reader.Read())
    {
         scriptNotes = reader["scriptnotes"].ToString();
    }
    reader.Close();
    cnn.Close();
    }
    return scriptNotes;
}

和FirstReadViewModel如下：

public FirstReadViewModel()
{
        var dbFunctions = new DataLayer();
        this.ScriptNotes = dbFunctions.GetFirstReadNotes();
}

您应该使用接口将DataLayer注入到FirstReadViewModel中，并稍微更改代码

创建一个接口

interface IFirstReadViewModelDAL
{
    string GetFirstReadNotes();
}

使用它，还可以使用的使用功能

   internal class DataLayer: IFirstReadViewModelDAL
    {
        public string GetFirstReadNotes()
        {
            string ScriptNotes;
            String dbConnectionString = @"Data Source =DB.sqlite";
            using(SQLiteConnection cnn = new SQLiteConnection(dbConnectionString))
            {
                cnn.Open();
                SQLiteCommand cmd = new SQLiteCommand(cnn);
                cmd.CommandText = "SELECT* FROM projects WHERE projectID = 1";
                using (SQLiteDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        ScriptNotes = reader["scriptnotes"].ToString();
                    }
                }
            }
            return ScriptNotes;
        }
    }

使用接口注入DataLayer

    private IFirstReadViewModelDAL dbFunctions;
    private string _scriptNotes;
    public string ScriptNotes    //binded in the View
    {
        get { return _scriptNotes; }
        set { _scriptNotes = value; RaisePropertyChanged("ScriptNotes"); }
    }
    public FirstReadViewModel(IFirstReadViewModelDAL injectDAL)
    {
        dbFunctions = injectDAL;
    }
    private void LoadData();
    {
        // use your dbFunctions
    }

要注入它，你需要一个单独的类，比如

public class Controller
{
    public static FirstReadViewModel getNewFirstReadViewModel()
    {
        var dal = new DataLayer();
        var vm = new FirstReadViewModel(dal);
        return vm;
    }
}
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