<ProgressBar HorizontalAlignment="Center" VerticalAlignment="Top" Margin="0,620,0,0"
                     Width="300" Height="20" Background="White"

                     IsIndeterminate="True" Foreground="White"/>

备注：
 IsIndeterminate＝"True"为progressDialog
 IsIndeterminate＝"False"为progressBar

摘自 xiechengfa的专栏