我试图在UWP应用程序中创建和写入文件。第一次执行时,它工作正常;第二次,它覆盖了第一个内容,而文件仅包含第二次执行中的内容。
Windows.Storage.StorageFolder Location = ApplicationData.Current.LocalFolder;
var lstfiles = await Location.GetFilesAsync(CommonFileQuery.OrderByName);
var foundfile = lstfiles.Where(x => x.Name==Test.dat").FirstOrDefault();
if (foundfile==null)
{
StorageFile fil = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("Test.dat");
//StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.GetFileAsync("Test.dat");
using (IRandomAccessStream writeStream = await fil.OpenAsync(FileAccessMode.ReadWrite))
{
System.IO.Stream s = writeStream.AsStreamForWrite();
System.Xml.XmlWriterSettings settings = new System.Xml.XmlWriterSettings();
settings.Async = true;
using (System.Xml.XmlWriter writer = System.Xml.XmlWriter.Create(s, settings))
{
writer.WriteStartElement("Order");
writer.WriteElementString("OrderID", "y1");
writer.WriteElementString("OrderTotal", "y2");
writer.WriteElementString("Customer", "y3");
writer.WriteElementString("Phone", "y4");
writer.Flush();
await writer.FlushAsync();
}
}
}
else
{
StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.GetFileAsync("Test.dat");
using (IRandomAccessStream writeStream = await file.OpenAsync(FileAccessMode.ReadWrite))
{
System.IO.Stream s = writeStream.AsStreamForWrite();
System.Xml.XmlWriterSettings settings = new System.Xml.XmlWriterSettings();
settings.Async = true;
using (System.Xml.XmlWriter writer = System.Xml.XmlWriter.Create(s, settings))
{
writer.WriteStartElement("Order");
writer.WriteElementString("OrderID", "v51");
writer.WriteElementString("OrderTotal", "v2");
writer.WriteElementString("Customer", "v3");
writer.WriteElementString("Phone", "v4");
// await FileIO.AppendTextAsync(file, writer.ToString());
writer.Flush();
await writer.FlushAsync();
}
}
}
尽管您必须先阅读整个Xml,然后才能添加新节点,而无论性能如何下降,都应该使用更简洁的方法
StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("Test.dat", CreationCollisionOption.OpenIfExists);
var info = await file.GetBasicPropertiesAsync();
XDocument xDocument = null;
if(info.Size > 0)
/* read existing file here */
else
/* create an empty document here */
XElement root = xDocument.Element("Root");
IEnumerable<XElement> rows = root.Descendants("Order");
XElement firstRow = rows.First();
firstRow.AddBeforeSelf(
new XElement("Order",
new XElement("OrderID", "y1"),
new XElement("OrderTotal", "y2"),
new XElement("Customer", "y3"),
new XElement("Phone", "y4")));
await FileIO.WriteTextAsync(file, xDocument.ToString());
这样,您就不会重复代码。
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