WinForm 使用Html生成的.xlsx文件打不开

Question

winform 使用html导出RadChartView中数据到Excel文件，xls格式没问题，xlsx文件打不开。
提示如下：Excel 无法打开文件“*.xlsx”,因为文件格式或文件扩展名无效。请确定文件未损坏，并且文件扩展名与文件的格式匹配。
代码如下：
try
{
StringBuilder htmlStr = new StringBuilder();
htmlStr.Append("");
htmlStr.Append("

");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
if (this.radChartView1.Series.Count > 0)
{
foreach (var lineSeries in this.radChartView1.Series)
{
htmlStr.Append("");
}
}
htmlStr.Append("");
htmlStr.Append("

"); htmlStr.Append(""); htmlStr.Append($""); foreach (var dataPoint in lineSeries.DataPoints) { CategoricalDataPoint point = dataPoint as CategoricalDataPoint; if (point != null) { htmlStr.Append(""); htmlStr.Append($""); htmlStr.Append($""); htmlStr.Append(""); } } htmlStr.Append(" {lineSeries.Name} {point.Category} {point.Label} "); htmlStr.Append("

");
htmlStr.Append("");
htmlStr.Append("");

            using (SaveFileDialog saveFileDialog = new SaveFileDialog())
            {
                saveFileDialog.Filter = $"xls files(*.xls)|*.xls|xlsx files(*.xlsx)|*.xlsx";
                saveFileDialog.RestoreDirectory = true;
                if (saveFileDialog.ShowDialog() == DialogResult.OK)
                {
                    StreamWriter writer = new StreamWriter(saveFileDialog.FileName, false);
                    writer.WriteLine(htmlStr.ToString());
                    writer.Close();
                }
            }
        }
        catch (Exception exception)
        {
            RadMessageBox.Show(exception.Message);
        }

Answer 1

代码贴出来好像有点问题，重新贴代码：
try
{
StringBuilder htmlStr = new StringBuilder();
htmlStr.Append("");
htmlStr.Append("

");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
htmlStr.Append("");
if (this.radChartView1.Series.Count > 0)
{
foreach (var lineSeries in this.radChartView1.Series)
{
htmlStr.Append("");
}
}
htmlStr.Append("");
htmlStr.Append("

"); htmlStr.Append(""); htmlStr.Append($""); foreach (var dataPoint in lineSeries.DataPoints) { CategoricalDataPoint point = dataPoint as CategoricalDataPoint; if (point != null) { htmlStr.Append(""); htmlStr.Append($""); htmlStr.Append($""); htmlStr.Append(""); } } htmlStr.Append(" {lineSeries.Name} {point.Category} {point.Label} "); htmlStr.Append("

");
htmlStr.Append("");
htmlStr.Append("");

            using (SaveFileDialog saveFileDialog = new SaveFileDialog())
            {
                saveFileDialog.Filter = $"xls files(*.xls)|*.xls|xlsx files(*.xlsx)|*.xlsx";
                saveFileDialog.RestoreDirectory = true;
                if (saveFileDialog.ShowDialog() == DialogResult.OK)
                {
                    StreamWriter writer = new StreamWriter(saveFileDialog.FileName, false);
                    writer.WriteLine(htmlStr.ToString());
                    writer.Close();
                }
            }
        }
        catch (Exception exception)
        {
            RadMessageBox.Show(exception.Message);
        }