UWP read temporary files and documentation

Question

I have tried to use the windows app documentation to read temporary files (read and write) on UWP. But I couldn't make it work using the documentation as in the example at this link below

Documentation in this parte:

async void WriteTimestamp()
{
  Windows.Globalization.DateTimeFormatting.DateTimeFormatter formatter = 
   new Windows.Globalization.DateTimeFormatting.DateTimeFormatter("longtime");

StorageFile sampleFile = await temporaryFolder.CreateFileAsync("dataFile.txt", 
   CreateCollisionOption.ReplaceExisting);
await FileIO.WriteTextAsync(sampleFile, formatter.Format(DateTimeOffset.Now));
}

But soon I have a problem with "temporaryFolder". It's says doesn't exist in the current context. So... I try: (1) add "using Windows.Storage;" don't work... (2) declare outside:

public Windows.Storage.StorageFolder temporaryFolder { get; set; }

this time the code says there is no error, but when I start the program it stops. " 'Object reference not set to an instance of an object.' App12UIWindows.Page2.temporaryFolder.get return null."

So I tried a solution from here (stackoverflow) and it worked. Link: Alternative Solution

My question is: why it go wrong? the documentation is correct or is it something else? or am I searching in the wrong place? My code:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using System.Collections.ObjectModel;
using Windows.Storage;
using System.Threading.Tasks;


namespace App12UIWindows
{
/// <summary>

/// </summary>
public sealed partial class Page2 : Page
{
    public Page2()
    {
        this.InitializeComponent();

        SaveTempFunc();
        readMyFileTemp();
    }

    public Windows.Storage.StorageFolder temporaryFolder { get; set; }
    

    async void SaveTempFunc()
    {


        StorageFile salvandoClientesT = await 
        temporaryFolder.CreateFileAsync("textOf_Information.txt") ;
        await FileIO.WriteTextAsync(salvandoClientesT,"test .. just like that... and 
        anothers words to a file");


    }
    //Fim salvando memória temporária

    //Lendo na memória temporária arquivo de texto
    async void readMyFileTemp()
    {
        try
        {
            StorageFile lendoTextoSalvo = await 
            temporaryFolder.GetFileAsync("textOf_Information.txt");
            String timestamp = await FileIO.ReadTextAsync(lendoTextoSalvo);
           

         }
        catch (Exception)
         {

         }

       }


    }



 }

Sorry for the bad english :)

score 1 · Accepted Answer · answered Jun 25 '21 at 06:41

1

'Object reference not set to an instance of an object.' App12UIWindows.Page2.temporaryFolder.get return null."

The problem is that you just declare temporaryFolder, but have not apply reference to temporaryFolder. Please refer the document mentioned above. pass ApplicationData.Current.TemporaryFolder to temporaryFolder variable.

public Windows.Storage.StorageFolder temporaryFolder { get; set; } = ApplicationData.Current.TemporaryFolder;

answered Jun 25 '21 at 06:41

Nico Zhu

32,367
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Thanks! this works! And a edit the line "temporaryFolder.CreateFileAsync("textoComClientes.txt", CreationCollisionOption.ReplaceExisting) ;" to exit a exception chatch. I'm going to study the code and links placed here. Thank you again. Documentation still difficult for me to understand. :) – Bommu Perneta Jun 25 '21 at 13:34

UWP read temporary files and documentation

1 Answers1