<hc:Window x:Class="Bddk.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:System="clr-namespace:System;assembly=mscorlib"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:hc="https://handyorg.github.io/handycontrol" xmlns:local="clr-namespace:Bddk"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="800" Height="450"
    UseLayoutRounding="True" WindowState="Maximized"
    mc:Ignorable="d">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition Width="3*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition />
        </Grid.RowDefinitions>
        <StackPanel Grid.ColumnSpan="2" Orientation="Horizontal">
            <ComboBox ItemsSource="{Binding Yıllar}" SelectedItem="{Binding SeçiliYıl}" />
            <ComboBox ItemsSource="{Binding Aylar}" SelectedItem="{Binding SeçiliAy}" />
            <ComboBox SelectedItem="{Binding ParaBirimi}">
                <System:String>TL</System:String>
                <System:String>USD</System:String>
            </ComboBox>
            <hc:CheckComboBox x:Name="CheckComboBox"
                MinWidth="200" MaxWidth="400"
                DisplayMemberPath="Value"
                ItemsSource="{Binding Taraf}"
                SelectionChanged="CheckComboBox_SelectionChanged"
                Style="{StaticResource CheckComboBoxPlus}" />
            <Button Click="Button_Click" Content="İNDİR" />
        </StackPanel>
        <ListBox Grid.Row="1" SelectedIndex="{Binding SeçiliVeri}">
            <System:String>Bilanço</System:String>
            <System:String>Kar Zarar</System:String>
            <System:String>Krediler</System:String>
            <System:String>Tüketici Kredileri</System:String>
            <System:String>Sektörel Kredi Dağılımı</System:String>
            <System:String>KOBİ Kredileri</System:String>
            <System:String>Sendikasyon Seküritizasyon Kredileri</System:String>
            <System:String>Menkul Kıymetler</System:String>
            <System:String>Mevduat Türler İtibarıyla</System:String>
            <System:String>Mevduat Vade İtibarıyla</System:String>
            <System:String>Likidite Durumu</System:String>
            <System:String>Sermaye Yeterliliği</System:String>
            <System:String>Yabancı Para Pozisyonu</System:String>
            <System:String>Bilanço Dışı İşlemler</System:String>
            <System:String>Rasyolar</System:String>
            <System:String>Diğer Bilgiler</System:String>
            <System:String>Yurt Dışı Şube Rasyoları</System:String>
        </ListBox>
        <DataGrid x:Name="Dg"
            Grid.Row="1" Grid.Column="1" />
    </Grid>
</hc:Window>

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using ExcelDataReader;

namespace Bddk
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : HandyControl.Controls.Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
            Taraf.Add(10001, "Sektör");
            Taraf.Add(10002, "Mevduat");
            Taraf.Add(10003, "Mevduat Yerli");
            Taraf.Add(10004, "Mevduat Kamu");
            Taraf.Add(10005, "Mevduat Yabancı");
            Taraf.Add(10006, "Katılım");
            Taraf.Add(10007, "Kalkınma ve Yatırım");
            Taraf.Add(10008, "Yerli Özel");
            Taraf.Add(10009, "Kamu");
            Taraf.Add(10010, "Yabancı");
        }

        public IEnumerable<int> Aylar { get; set; } = Enumerable.Range(1, DateTime.Now.Month);

        public string ParaBirimi { get; set; } = "TL";

        public int SeçiliAy { get; set; } = 1;

        public int SeçiliVeri { get; set; } = 0;

        public int SeçiliYıl { get; set; } = DateTime.Now.Year;

        public Dictionary<int, string> Taraf { get; set; } = new Dictionary<int, string>();

        public string TarafMetin { get; set; }

        public IEnumerable<int> Yıllar { get; set; } = Enumerable.Range(DateTime.Now.Year - 20, 21);

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            if (TarafMetin is null)
            {
                MessageBox.Show("Taraf Bilgisi Seçin");
                return;
            }
            string adres = $"https://www.bddk.org.tr/BultenAylik/tr/Home/BasitExceleAktar?tabloNo={SeçiliVeri + 1}&yil={SeçiliYıl}&ay={SeçiliAy}&paraBirimi={ParaBirimi}&{TarafMetin}";
            string fileName;
            using (WebClient client = new WebClient())
            {
                fileName = Path.GetTempPath() + Guid.NewGuid().ToString() + ".xlsx";
                client.DownloadFile(adres, fileName);
            }

            using (FileStream stream = File.Open(fileName, FileMode.Open, FileAccess.Read))
            {
                using (IExcelDataReader reader = ExcelReaderFactory.CreateReader(stream))
                {
                    Dg.ItemsSource = reader.AsDataSet().Tables[0].DefaultView;
                }
            }
        }

        private void CheckComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            string data = "";
            for (int i = 0; i < CheckComboBox.SelectedItems.Count; i++)
            {
                KeyValuePair<int, string> item = (KeyValuePair<int, string>)CheckComboBox.SelectedItems[i];
                data += "taraf[" + i + "]=" + item.Key + "&";
            }
            TarafMetin = data;
        }
    }
}