Windows Phone 學習 在程序中調用直接撥打電話

 <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <StackPanel>
                <TextBlock>顯示名：</TextBlock>
                <TextBox Name="txtDisplayName"/>
                <TextBlock Margin="0,13,0,0">電話號碼：</TextBlock>
                <TextBox Name="txtPhoneNumber">
                    <TextBox.InputScope>
                        <InputScope>
                            <InputScopeName NameValue="NameOrPhoneNumber"/>
                        </InputScope>
                    </TextBox.InputScope>
                </TextBox>
                <Button Margin="0,8,0,0" Content="確定" HorizontalAlignment="Left" Click="btnOK_Click"/>
            </StackPanel>
        </Grid>
    </Grid>

 private void btnOK_Click(object sender, RoutedEventArgs e)
        {
            if (txtPhoneNumber.Text == "")
            {
                MessageBox.Show("請輸入目標電話號碼。");
                return;
            }
            // 1、實例化
            PhoneCallTask MyCall = new PhoneCallTask();
            // 2、設置屬性值
            MyCall.DisplayName = txtDisplayName.Text;
            MyCall.PhoneNumber = txtPhoneNumber.Text;
            // 3、顯示應用程序界面
            MyCall.Show();
        }