文件名未显示在xamarin.forms的Entry行中

Question

我正在使用Xamarin.Forms应用。我需要浏览并打开文件夹中的文件，当我尝试这样做并选择文件时，文件路径不会显示在输入行中。这是我的代码，请告诉我应该改变什么？

public string FileName
{
    get { return fileName; }
    set
    {
        fileName = value;
        PropertyChanged(this, new PropertyChangedEventArgs("csv_file"));
    }
}

private Plugin.FilePicker.Abstractions.FileData file = default(Plugin.FilePicker.Abstractions.FileData);

public async void OnBrowse(object o, EventArgs args)
{
    this.file = await CrossFilePicker.Current.PickFile();
    if (this.file == null)
    {
        return;
    }

    string extensionType = this.file.FileName.Substring(this.file.FileName.LastIndexOf(".", StringComparison.Ordinal) 
        + 1, this.file.FileName.Length - this.file.FileName.LastIndexOf(".", StringComparison.Ordinal) - 1).ToLower();

    if (extensionType.Equals("csv"))
    {
        csv_file.SetValue((BindableProperty.Create("csv_file", typeof(string), typeof(Entry), null, BindingMode.TwoWay, null)), fileName);
    }
    else
    {
        await this.DisplayAlert("Name of the file:" + file.FileName + " and path too file: " + file.FilePath, "File info", "OK");
    }
}

这是xaml代码

         <StackLayout Orientation="Horizontal" 
                 HorizontalOptions="FillAndExpand">
            <Entry x:Name="csv_file" Placeholder="" WidthRequest="150">
            </Entry>
            <Button BackgroundColor="Gray" TextColor="Black" 
             WidthRequest="40" Text="...." Clicked="OnBrowse"/>
        </StackLayout>