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 ");

             }
             else
            {
                  outputText.Append(item.Name + " ");
            }
       }

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(500,500);
            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(0))
            {
                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(0))
            {
                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(0))
                {
                    using (var destinationStream = await destinationFile.OpenAsync(FileAccessMode.ReadWrite))
                    {
                        using (var destinationOutputStream = destinationStream.GetOutputStreamAt(0))
                        {
                            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 )

获取文件的顶级属性(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！