Windows Phone 学习 在程序中调用直接拨打电话

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
<StackPanel>
<TextBlock>显示名：</TextBlock>
<TextBox Name="txtDisplayName"/>
<TextBlock Margin="0,13,0,0">电话号码：</TextBlock>
<TextBox Name="txtPhoneNumber">
<TextBox.InputScope>
<InputScope>
<InputScopeName NameValue="NameOrPhoneNumber"/>
</InputScope>
</TextBox.InputScope>
</TextBox>
<Button Margin="0,8,0,0" Content="确定" HorizontalAlignment="Left" Click="btnOK_Click"/>
</StackPanel>
</Grid>
</Grid>

private void btnOK_Click(object sender, RoutedEventArgs e)
{
if (txtPhoneNumber.Text == "")
{
MessageBox.Show("请输入目标电话号码。");
return;
}
// 1、实例化
PhoneCallTask MyCall = new PhoneCallTask();
// 2、设置属性值
MyCall.DisplayName = txtDisplayName.Text;
MyCall.PhoneNumber = txtPhoneNumber.Text;
// 3、显示应用程序界面
MyCall.Show();
}