MainWindow.xaml

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <DockPanel LastChildFill="False" Background="AliceBlue">
        <DockPanel.DataContext>
            <local:ViewModel/>
        </DockPanel.DataContext>
        <ProgressBar Height="40" Margin="50 150 50 0" DockPanel.Dock="Top" Value="{Binding Progress}" Maximum="{Binding Maxlength}"/>
        <Button FontSize="22" Width="150" Height="50" Margin="0 50 0 0" DockPanel.Dock="Top" Content="下载" Command="{Binding DownloadStart}" CommandParameter="{Binding}" IsEnabled="{Binding Enable}"/>
        <Button FontSize="22"  Width="150" Height="50" Margin="0 25 0 0" DockPanel.Dock="Top" Content="取消" Command="{Binding Downloadcancel}" CommandParameter="{Binding}"/>
    </DockPanel>
</Window>