原文:Windows 10开发基础——文件、文件夹和库（一）
主要内容：
1.枚举查询文件和文件夹
2.文本文件读写的三种方法——创建写入和读取文件
3.获得文件的属性
枚举查询文件和文件夹
先了解一下文件查询的几个方法：
StorageFolder.GetFilesAsync: 获取当前文件夹中的所有文件，返回一个 IReadOnlyList<StorageFile>集合
IReadOnlyList<StorageFile> fileList =await picturesFolder.GetFilesAsync();
StorageFolder.GetFolersAsync:获取当前文件夹中的所有子文件夹，返回一个IReadOnlyList<StorageFolder>集合
IReadOnlyList<StorageFolder> folderList =await picturesFolder.GetFoldersAsync();
StorageFolder.GetItemsAsync:获取当前文件夹中的所有文件和子文件夹，返回一个IReadOnlyList<IStorageItem>集合
ReadOnlyList<IStorageItem> itemsList =await picturesFolder.GetItemsAsync();
e.g:
StorageFolder picturesFolder = KnownFolders.PicturesLibrary;
StringBuilder outputText = new StringBuilder();
IReadOnlyList<IStorageItem> itemsList = await picturesFolder.GetItemsAsync();//获取当前文件夹中的所有文件和子文件夹
foreach (var item in itemsList)
{
if (item is StorageFolder)
{
outputText.Append(item.Name + " folder\n");
}
else
{
outputText.Append(item.Name + "\n");
}
}
还要注意一下查询某个位置中的文件并枚举匹配的文件（CommonFolderQuery可取的枚举值很多，转到定义了解一下咯）
StorageFolder picturesFolder = KnownFolders.PicturesLibrary;
StorageFolderQueryResult queryResult = picturesFolder.CreateFolderQuery(CommonFolderQuery.GroupByMonth);//这一行是主要代码，将同一月份的文件归类到一个文件夹
IReadOnlyList<StorageFolder> folderList = await queryResult.GetFoldersAsync();//检索结果集中的文件夹列表
StringBuilder outputText = new StringBuilder();
foreach (StorageFolder folder in folderList)
{
IReadOnlyList<StorageFile> fileList = await folder.GetFilesAsync();
outputText.AppendLine(folder.Name + " (" + fileList.Count + ")");//folder.Name的值类似于：2014年12月
foreach (StorageFile file in fileList)
{
outputText.AppendLine(" " + file.Name);
}
}
然后我们再来看一个实例：
查询出图片库根目录中的所有图片，然后将图片文件名显示在一个列表中，点击列表的某一项，Image显示对应的图片。
图片库对应于电脑中的下图：
1.在Package.appxmanifest中的“功能”节点中选中“图片库”
2.界面布局
一个按钮，一个ListView，一个Image
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="auto"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<Button x:Name="button" Content="点击查看图片库" HorizontalAlignment="Center" Margin="0,10,0,10" VerticalAlignment="Top" Click="button_Click" Width="161"/>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition></ColumnDefinition>
<ColumnDefinition></ColumnDefinition>
</Grid.ColumnDefinitions>
<ListView SelectionMode="Single" x:Name="lv_file" Margin="10" Grid.Column="0" IsEnabled="True" SelectionChanged="lv_file_SelectionChanged" >
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" FontSize="20" Margin="0,5,0,0" Foreground="Black"></TextBlock>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<Image x:Name="img" Grid.Column="1" Source="Assets/Images/nokiagood2.jpg"></Image>
</Grid>
</Grid>
3.后台代码
loadData方法用来获取图片库中的图片，并将文件名绑定的ListView控件上，我们可以在页面的构造函数里面调用它，在应用程序启动之后就显示列表数据。
在显示图片时用到了WriteableBitmap，它用来创建可显示和更新的位图对象，通过将图片文件写入流（IRandomAccessStream）中，然后从流中读取图形数据并保存到位图中来显示图片。
GetFileAsync()方法根据传入的string来获取指定的文件
private async void loadData()
{//获取图片库中的图片，并将文件名绑定的ListView控件上 picturesFolder = KnownFolders.PicturesLibrary;//获取图片库
List<string> filestrlists = new List<string>();
IReadOnlyList<StorageFile> fileList =await picturesFolder.GetFilesAsync(); //获取当前文件夹中的所有文件
foreach (StorageFile file in fileList)
{
filestrlists.Add(file.Name);
}
lv_file.ItemsSource = filestrlists;
} private void button_Click(object sender, RoutedEventArgs e)
{
loadData();
} private async void lv_file_SelectionChanged(object sender, SelectionChangedEventArgs e)
{//ListView的选中事件，选择某一项时显示对应得图片 WriteableBitmap writeableBitmap = new WriteableBitmap(,);
string filename = lv_file?.SelectedItem as string; if (filename != null)
{
StorageFile file = await picturesFolder?.GetFileAsync(filename);
IRandomAccessStream stream = await file?.OpenAsync(FileAccessMode.Read);
await writeableBitmap.SetSourceAsync(stream);
img.Source = writeableBitmap;
}
}
4.运行测试。
文本文件读写的三种方法——创建写入和读取文件
方法一：使用FileIO类WriteTextAsync和ReadTextAsync方法
await FileIO.WriteTextAsync(sampleFile,tb_txt.Text.Trim());//写
string text = await FileIO.ReadTextAsync(sampleFile); //读
方法二：使用缓冲区（Buffer）
写：
var buffer = CryptographicBuffer.ConvertStringToBinary(tb_txt.Text.Trim(), BinaryStringEncoding.Utf8);
await FileIO.WriteBufferAsync(sampleFile, buffer);
读：
var buffer = await FileIO.ReadBufferAsync(sampleFile);
using (var dataReader =DataReader.FromBuffer(buffer))
{
string text = dataReader.ReadString(buffer.Length);
}
方法三：使用流（Stream）
写：
var stream = await sampleFile.OpenAsync(FileAccessMode.ReadWrite);
using (var outputStream = stream.GetOutputStreamAt(0))
{
using (var dataWriter = new DataWriter(outputStream))
{
dataWriter.WriteString(tb_txt.Text.Trim());
await dataWriter.StoreAsync();
await outputStream.FlushAsync();
}
}
stream.Dispose();
读：
var stream = await sampleFile.OpenAsync(FileAccessMode.ReadWrite);
ulong size = stream.Size;
using (var inputStream = stream.GetInputStreamAt(0))
{
using (var dataReader = new DataReader(inputStream))
{
uint numBytesLoaded = await dataReader.LoadAsync((uint)size);
string text = dataReader.ReadString(numBytesLoaded);
}
接下来是常规演示：在文本框里输入文本，然后点击create按钮创建并写入文件，然后get按钮读出文件中的内容。
界面很简单，直接上图：
代码也容易理解，我就直接贴（注意一些变量的定义是可以提到方法外面的，为了演示，我就都写在方法里面了，实际使用的时候根据情况处理就好了）。
对应于方法一：
private async void btn_createFile_Click(object sender, RoutedEventArgs e)
{
// 创建一个文件（sample.txt）; 如果存在就替换.
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile =await folder.CreateFileAsync("sample.txt",CreationCollisionOption.ReplaceExisting);
await FileIO.WriteTextAsync(sampleFile,tb_txt.Text.Trim());
} private async void btn_getFile_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile =await folder.GetFileAsync("sample.txt");
string text = await FileIO.ReadTextAsync(sampleFile);
showmsg(text);
} private async void showmsg(string content)
{
MessageDialog msg = new MessageDialog(content, "info");
await msg.ShowAsync();
}
对应于方法二：
private async void btn_cerateFileBuffer_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile = await folder.CreateFileAsync("sample.txt", CreationCollisionOption.ReplaceExisting); var buffer = CryptographicBuffer.ConvertStringToBinary(tb_txt.Text.Trim(), BinaryStringEncoding.Utf8); await FileIO.WriteBufferAsync(sampleFile, buffer);
}
private async void btn_getFileBuffer_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile = await folder.GetFileAsync("sample.txt");
var buffer = await FileIO.ReadBufferAsync(sampleFile);
string text;
using (var dataReader =DataReader.FromBuffer(buffer))
{
text = dataReader.ReadString(buffer.Length);
}
showmsg(text);
}
对应于方法三：
private async void btn_createFileStream_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile =await folder.CreateFileAsync("sample.txt", CreationCollisionOption.ReplaceExisting);
var stream = await sampleFile.OpenAsync(FileAccessMode.ReadWrite);
using (var outputStream = stream.GetOutputStreamAt())
{
using (var dataWriter = new DataWriter(outputStream))
{
dataWriter.WriteString(tb_txt.Text.Trim());
await dataWriter.StoreAsync();
await outputStream.FlushAsync();
}
}
stream.Dispose(); }
private async void btn_getFileStream_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile sampleFile = await folder.GetFileAsync("sample.txt"); var stream = await sampleFile.OpenAsync(FileAccessMode.ReadWrite);
ulong size = stream.Size;
using (var inputStream = stream.GetInputStreamAt())
{
string text;
using (var dataReader = new DataReader(inputStream))
{
uint numBytesLoaded = await dataReader.LoadAsync((uint)size);
text = dataReader.ReadString(numBytesLoaded);
}
showmsg(text);
}
}
然后我们再来看一个实例：
将部分程序界面截图保存至应用程序存储，然后进行读取。还将演示如何保存至图片库。
1.涉及到操作图片库，首先也要去Package.appxmanifest中的“功能”节点中选中“图片库”。（以后不再赘述）
2.界面布局
注意grid和cgrid都是我们要截图保存的UI元素，都要给它们一个Background。（你可以试试，不给是什么情况）
<Grid x:Name="grid" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<Grid Margin="10" x:Name="cgrid" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Button x:Name="btn_createImg" Content="create a picture file" HorizontalAlignment="Left" Margin="12,33,0,0" VerticalAlignment="Top" Click="btn_createImg_Click"/>
<Button x:Name="btn_getImg" Content="get a picture file" HorizontalAlignment="Left" Margin="206,33,0,0" VerticalAlignment="Top" Click="btn_getImg_Click"/>
<Image x:Name="img_original" HorizontalAlignment="Left" Margin="12,117,0,0" Source="Assets/Images/nokiagood2.jpg" Stretch="UniformToFill" VerticalAlignment="Top" Width="338"/>
<Button x:Name="btn_save" Content="save to photos" HorizontalAlignment="Left" Margin="12,80,0,0" VerticalAlignment="Top" Width="128" Click="btn_save_Click"/>
</Grid>
<Image Grid.Row="1" x:Name="img_create" HorizontalAlignment="Left" Height="217" Margin="12,20,0,0" Stretch="UniformToFill" VerticalAlignment="Top" Width="338"/>
</Grid>
3.后台代码
创建图片文件并保存至应用程序存储中。RenderTargetBitmap、BitmapEncoder类需要重点理解一下。
private async void btn_createImg_Click(object sender, RoutedEventArgs e)
{
renderTargetBitmap = new RenderTargetBitmap();//RenderTargetBitmap类可以将可视化对象转换为位图
await renderTargetBitmap.RenderAsync(cgrid); var pixelBuffer = await renderTargetBitmap.GetPixelsAsync(); var folder = ApplicationData.Current.LocalFolder;
var file = await folder.CreateFileAsync("screenshot.png",CreationCollisionOption.ReplaceExisting); using (var stream=await file.OpenAsync(FileAccessMode.ReadWrite))
{
var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, stream);//BitmapEncoder类包含创建、编辑和保存图像的各种方法
encoder.SetPixelData(BitmapPixelFormat.Bgra8,
BitmapAlphaMode.Ignore,
(uint)renderTargetBitmap.PixelWidth,
(uint)renderTargetBitmap.PixelHeight,
DisplayInformation.GetForCurrentView().LogicalDpi,
DisplayInformation.GetForCurrentView().LogicalDpi,
pixelBuffer.ToArray()); //设置图像有关帧的像素数据
await encoder.FlushAsync();//提交和刷新图像数据
}
}
从应用程序中读取显示图片
private async void btn_getImg_Click(object sender, RoutedEventArgs e)
{
//方法一：类似于实例一中的方法来展示图片
WriteableBitmap writeableBitmap = new WriteableBitmap(renderTargetBitmap.PixelWidth, renderTargetBitmap.PixelHeight);
var folder = ApplicationData.Current.LocalFolder;
var file = await folder.GetFileAsync("screenshot.png"); IRandomAccessStream stream = await file?.OpenAsync(FileAccessMode.Read);
await writeableBitmap.SetSourceAsync(stream);
img_create.Source = writeableBitmap; //方法二：通过应用文件的Uri方案来展示图片
//BitmapImage bitmapImage = new BitmapImage(new Uri("ms-appdata:///local/screenshot.png", UriKind.Absolute));
//img_create.Source = bitmapImage;
}
将图片保存至图片库。
private async void btn_save_Click(object sender, RoutedEventArgs e)
{
WriteableBitmap writeableBitmap = new WriteableBitmap(renderTargetBitmap.PixelWidth, renderTargetBitmap.PixelHeight); var folder = ApplicationData.Current.LocalFolder;
var sourcefile = await folder.GetFileAsync("screenshot.png");//获取图片screenshot.png StorageFile destinationFile = await KnownFolders.CameraRoll.CreateFileAsync("screenshot.png",CreationCollisionOption.ReplaceExisting);//在图片库中的CameraRoll文件夹中创建文件
using (var sourceStream = await sourcefile.OpenReadAsync())
{
using (var sourceInputStream = sourceStream.GetInputStreamAt())
{
using (var destinationStream = await destinationFile.OpenAsync(FileAccessMode.ReadWrite))
{
using (var destinationOutputStream = destinationStream.GetOutputStreamAt())
{
await RandomAccessStream.CopyAndCloseAsync(sourceInputStream, destinationStream);//复制源流到目标流
}
}
}
}
}
4.运行测试。
获得文件的属性
(msdn: https://msdn.microsoft.com/zh-cn/library/windows/apps/mt186454.aspx )
获取文件的*属性(这些属性包括文件属性、内容类型、创建日期、显示名称和文件类型等。)
StringBuilder fileProperties = new StringBuilder();
fileProperties.AppendLine("File name: " + file.Name);
fileProperties.AppendLine("File type: " + file.FileType);
获取文件的基本属性
多数基本属性都是通过先调用StorageFile.GetBasicPropertiesAsync()方法获得的。此方法会返回一个BasicProperties对象，该对象将定义项（文件或文件夹）的大小属性，以及上次修改项的时间。
BasicProperties basicProperties = await file.GetBasicPropertiesAsync();
string fileSize = string.Format("{0:n0}", basicProperties.Size);
fileProperties.AppendLine("File size: " + fileSize + " bytes");
fileProperties.AppendLine("Date modified: " + basicProperties.DateModified);
获取文件的扩展属性
扩展属性只能通过以下方法获得：将代表将要检索的属性名称的 String 对象的 IEnumerable 集合传递到BasicProperties.RetrievePropertiesAsync 方法。之后此方法会返回一个 IDictionary 集合。然后可以按名称或通过索引从这个集合中检索每个扩展属性。
const string dateAccessedProperty = "System.DateAccessed";
const string fileOwnerProperty = "System.FileOwner"; var folder = KnownFolders.PicturesLibrary;
var query = folder.CreateFileQuery();
var files = await query.GetFilesAsync(); foreach (StorageFile file in files)
{
StringBuilder fileProperties = new StringBuilder(); var propertyNames = new List<string>();
propertyNames.Add(dateAccessedProperty);
propertyNames.Add(fileOwnerProperty); IDictionary<string, object> extraProperties = await file.Properties.RetrievePropertiesAsync(propertyNames);
var propValue = extraProperties[dateAccessedProperty];
if (propValue != null)
{
fileProperties.AppendLine("Date accessed: " + propValue);
} propValue = extraProperties[fileOwnerProperty];
if (propValue != null)
{
fileProperties.AppendLine("File owner: " + propValue);
}
太晚了，这个不准备实例了。睡觉！