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[操作系统]Windows 10开发基础——文件、文件夹和库(二)


主要内容:

      使用选取器打开和保存文件

 

      关于文件、文件夹和库,如果深究其实还是有比较多的内容,我们这一次来学习一下选取器就收了。还有上篇博文中读写文本文件的三种方式可以细细体会一下。

      文件选取器包含文件打开选取器(FileOpenPicker、FolderPicker)和文件保存选取器(FileSavePicker),分别用来打开文件和保存文件,这两个选取器的使用方法大致相同。

    FileOpenPicker类:

  • ViewMode ,获取或设置文件选取器用来展示文件或文件夹的视图模式,属性值由PickerViewMode枚举来指定,该枚举有两个枚举值,List表示列表模式,Thumbnail表示缩略图模式

  • SuggestedStartLocation ,获取或设置文件选取器要呈现给用户的文件的初始位置。属性值由PickerLocationId枚举指定,此枚举一共有10个枚举值,自行转到定义进行查看。

  • FileTypeFilter,获取文件选择器显示的文件类型的集合,文件类型可以是".txt",".jpg"等,使用Add来进行添加。 

     注意我们设置的ViewMode和SuggestedStartLocation值在应用程序第一次运行之后,再切换其他值运行,有时候并不会起作用,应该是操作系统自己有记录,然后这个FileTypeFilter属性是必须指定的。

    FileOpenPicker picker = new FileOpenPicker();      //创建文件打开选取器
    picker.ViewMode = PickerViewMode.Thumbnail;       //将ViewMode的值设置为Thumbnail
    picker.SuggestedStartLocation =PickerLocationId.PicturesLibrary;  //将文件选取器打开文件的开始位置设置为图片库

    picker.FileTypeFilter.Add(".jpg");
    picker.FileTypeFilter.Add(".jpeg");
    picker.FileTypeFilter.Add(".png");

    FolderPicker类:

      该类的属性和用法与FileOpenPicker类似。  

      FolderPicker folderPicker = new FolderPicker();
      folderPicker.ViewMode = PickerViewMode.List;
      folderPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
      folderPicker.FileTypeFilter.Add("*");

    FileSavePicker类:

      该类我们经常使用到的3个属性是SuggestedStartLocation(同上)、FileTypeChoices、SuggestedFileName。FileTypeChoices是一个字典类型(IDictionary<System.String, IList<System.String>>),获取用户可选择分配到文件的有效文件类型的集合,SuggestedFileName 则是获取或设置文件保存选取器向用户建议的文件名。

     FileSavePicker picker = new FileSavePicker();

     picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;

     picker.FileTypeChoices.Add("Image", new List<string>() { ".jpg", ".jpeg", ".png", ".bmp", ".gif" });

     picker.SuggestedFileName =DateTime.Now.ToString("yyyyMMddhhmmss");

 

    我们来进行常规演示,首先是选取单个文件,多个文件,还有文件夹。

      选取并显示一张图片:

  private async void btn_pickpic_Click(object sender, RoutedEventArgs e)    {      FileOpenPicker picker = new FileOpenPicker();      picker.ViewMode = PickerViewMode.List;      picker.SuggestedStartLocation =PickerLocationId.PicturesLibrary;      picker.FileTypeFilter.Add(".jpg");      picker.FileTypeFilter.Add(".jpeg");      picker.FileTypeFilter.Add(".png");      storagefile = await picker.PickSingleFileAsync();      if (storagefile != null)      {        this.tb_pickedpic.Text = "Picked photo: " + storagefile.Name;        WriteableBitmap writeableBitmap = new WriteableBitmap(500, 500);        IRandomAccessStream stream = await storagefile?.OpenAsync(FileAccessMode.Read);        await writeableBitmap.SetSourceAsync(stream);        image.Source = writeableBitmap;      }      else      {        this.tb_pickedpic.Text = "Operation cancelled.";        image.Source = null;      }    }

       选取多张图片:

 private async void btn_pickmultipic_Click(object sender, RoutedEventArgs e)    {      var picker = new FileOpenPicker();      picker.ViewMode = PickerViewMode.Thumbnail;      picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;      picker.FileTypeFilter.Add(".jpeg");      picker.FileTypeFilter.Add(".png");      picker.FileTypeFilter.Add(".jpg");      IReadOnlyList<StorageFile> filelist =await picker.PickMultipleFilesAsync();      StringBuilder output = new StringBuilder("Picked files:");      if (filelist.Count>0)      {        foreach (var file in filelist)        {          output.Append(file.Name+"\n");        }      }      else      {        output.Append("none!");      }      Showmsg(output.ToString());    }

     Showmsg(output.ToString());是弹出对话框,显示所选择的图片。

      选取文件夹:

  private async void btn_pickfolder_Click(object sender, RoutedEventArgs e)    {      FolderPicker folderPicker = new FolderPicker();      folderPicker.ViewMode = PickerViewMode.List;      folderPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;      folderPicker.FileTypeFilter.Add("*");      StorageFolder folder = await folderPicker.PickSingleFolderAsync();      if (folder != null)      {        StorageApplicationPermissions.FutureAccessList.AddOrReplace("PickedFolderToken", folder);        Showmsg("Picked folder: " + folder.Name);      }      else      {        Showmsg("Operation cancelled.");      }    }

        接着是保存文件,首先是保存文本文件,然后将上面选取并显示的那张图片保存到另一文件夹。

        保存文本文件:

 private async void button_Click(object sender, RoutedEventArgs e)    {      FileSavePicker savePicker = new FileSavePicker();      savePicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;      savePicker.FileTypeChoices.Add("文本文件", new List<string>() { ".txt" });      savePicker.SuggestedFileName = "mytxt";           StorageFile file = await savePicker.PickSaveFileAsync();      if (file != null)      {        CachedFileManager.DeferUpdates(file);        if (tbxcontent.Text.Trim().Length > 0)        {          await FileIO.WriteTextAsync(file,tbxcontent.Text);          FileUpdateStatus status = await CachedFileManager.CompleteUpdatesAsync(file);          if (status == FileUpdateStatus.Complete)          {            this.tbInfo.Text = "File " + file.Name + " was saved.";          }          else          {            this.tbInfo.Text = "File " + file.Name + " couldn't be saved.";          }        }      }      else      {        this.tbInfo.Text = "Operation cancelled.";      }    }

          运行结果:

   

           保存上面选取并显示的那张图片到另一文件夹:     

  private async void btn_save_Click(object sender, RoutedEventArgs e)    {      FileSavePicker picker = new FileSavePicker();      picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;      picker.FileTypeChoices.Add("Image", new List<string>() { ".jpg", ".jpeg", ".png", ".bmp", ".gif" });      picker.SuggestedFileName =DateTime.Now.ToString("yyyyMMddhhmmss");      StorageFile file= await picker.PickSaveFileAsync();      if(file!=null&&storagefile!=null)      {        CachedFileManager.DeferUpdates(file);        IBuffer buffer = await FileIO.ReadBufferAsync(storagefile);      //storageFile是已经选中要保存的文件        await FileIO.WriteBufferAsync(file, buffer);        FileUpdateStatus status = await CachedFileManager.CompleteUpdatesAsync(file);      }    }

            运行结果:

          好了,这些就是关于文件选取器的一些内容了。下次见!