c# - 仅在选择选项卡时运行查询 WPF MVVM

Question

如果选择了某个选项卡并运行一些查询，我正在寻找一种方法是检查我的 ViewModel。这是我的场景:

我有 2 个选项卡 - Tab1 包含一个带有一些代码隐藏的数据网格，而 Tab2 只有一些绑定(bind)到我的 ViewModel 的文本框。两个选项卡共享一个数据选择器。当我从 Tab1 中的数据网格中选择一行时，日期更改会触发绑定(bind)到 Tab2 中的文本框的一堆查询，因为所有查询都使用所选月份作为参数。

这使得它非常无效，并且数据网格行选择变得非常慢。我怎样才能避免这种情况？设置我的 ViewModel 以检查是否选择了 Tab2 然后才运行查询的简单方法是什么？我正在考虑在 TabControl 中绑定(bind) selectedIndex，但我无法让它工作。我对此很陌生，我真的很感激一些帮助。

查看型号

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Location.Model;
using System.Windows.Controls;

namespace Location.ViewModel
{
    public class LocationViewModel: INotifyPropertyChanged
    {
        public LocationViewModel()
        {
            SetEfficiency();
        }

        private DateTime _mDate = DateTime.Now;

        public DateTime MDate
        {
            get { return _mDate; }
            set 
            {
                _mDate = value;
                OnPropertyChanged("MDate");
                SetEfficiency();
            }
        }

        decimal efficiency;

        public decimal Efficiency
        {
            get { return efficiency; }
            set
            {
                efficiency = value;
                OnPropertyChanged("Efficiency");
            }
        }

        DailyEntities db = new DailyEntities();

        private void SetEfficiency()
        {
            var month;
            int.TryParse(MDate.ToString("MM"), out month);
            Efficiency = Convert.ToDecimal(db.LocationKPI.Where(a => a.sMonth == month).Select(a => a.Efficiency).FirstOrDefault());
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName = null)
        {
            if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

MainWindow.xaml.cs

    public MainWindow()
    {
        InitializeComponent();

        DataContext = new LocationViewModel();

        string connectionString = "datasource=xx.xx.xxx.xxx;port=xxx;username=xxxxx;password=xxxxx";
        string sMonth = DateTime.Now.ToString("MM");
        string sYear = DateTime.Now.ToString("yyyy");

        MySqlConnection connection = new MySqlConnection(connectionString);

        MySqlCommand cmd = new MySqlCommand("Select * from MyTable where MONTH(Date) = @sMonth AND YEAR(Date) = @sYear", connection);

        try
        {
            connection.Open();
            cmd.Parameters.Add(new MySqlParameter("sMonth", sMonth));
            cmd.Parameters.Add(new MySqlParameter("sYear", sYear));

            DataTable dt = new DataTable();
            dt.Load(cmd.ExecuteReader());
            dtGrid.DataContext = dt;
            connection.Close();

        }

        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }



    }

    private void vDatePick_SelectedDateChanged(object sender, SelectionChangedEventArgs e)
    {

            string connectionString = "datasource=xx.xx.xxx.xxx;port=xxx;username=xxxxx;password=xxxxx";
            string sMonth = DateTime.Parse(vDatePick.Text).ToString("MM");
            string sYear = DateTime.Parse(vDatePick.Text).ToString("yyyy");
            string vDate = DateTime.Parse(vDatePick.Text).ToString("yyyy-MM-dd");

            MySqlConnection connection = new MySqlConnection(connectionString);
            MySqlCommand cmd = new MySqlCommand("Select * from MyTable where MONTH(Date) = @sMonth AND YEAR(Date) = @sYear", connection);


            try
            {

                connection.Open();
                cmd.Parameters.Add(new MySqlParameter("sMonth", sMonth));
                cmd.Parameters.Add(new MySqlParameter("sYear", sYear));
                DataTable dt = new DataTable();
                dt.Load(cmd.ExecuteReader());
                connection.Close();
                dtGrid.DataContext = dt;

            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

    }


    private void dtGrid_SelectedCellsChanged(object sender, SelectedCellsChangedEventArgs e)
    {

        DataRowView row_selected = dtGrid.SelectedItem as DataRowView;
        if (row_selected == null) return;
        vDatePick.Text = row_selected["Date"].ToString();
        txtHours.Text = row_selected["Hours"].ToString();

    }

谢谢

Answer 1

将您的 TabControl 添加到 SelectedIndex="{Binding SelectedTabIndex, Mode=TwoWay}

更改您的方法，如下所示:

private void vDatePick_SelectedDateChanged(object sender, SelectionChangedEventArgs e) 
{
    if(SelectedTabIndex == 1)
    {
    //... your code 
   }
}