UWP 读取临时文件和文档

Question

我尝试使用 windows 应用程序文档读取 UWP 上的临时文件（读写）。但是我无法使用下面 link

示例中的文档使其工作

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));
}

但很快我就遇到了“temporaryFolder”的问题。据说在当前上下文中不存在。所以... 我尝试：(1) 添加“使用 Windows.Storage;”不工作... (2) 对外声明：

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

这次代码说没有错误，但是当我启动程序时它停止了。 " 'Object reference not set to an instance of an object.' App12UIWindows.Page2.temporaryFolder.get return 空。

所以我从这里 (Whosebug) 尝试了一个解决方案并且它有效。 Link: Alternative Solution

我的问题是：为什么会出错？文档是正确的还是其他？还是我在错误的地方搜索？我的代码：

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)
         {

         }

       }


    }



 }

抱歉英语不好:)

Answer 1

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

问题是您只是声明了 temporaryFolder，但没有应用对 temporaryFolder 的引用。请参考上面提到的document。将 ApplicationData.Current.TemporaryFolder 传递给临时文件夹变量。

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

UWP 读取临时文件和文档

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