建立、寫入和讀取檔案

重要 API

• StorageFolder 類別
• StorageFile 類別 \(英文\)
• FileIO 類別

使用 StorageFile 物件讀取和寫入檔案。

注意

 如需完整範例，請參閱檔案存取範例 \(英文\)。

必要條件

• 了解通用 Windows 平台 (UWP) 應用程式的非同步程式設計

  您可以參閱在 C# 或 Visual Basic 中呼叫非同步 API，以了解如何在 C# 或 Visual Basic 中撰寫非同步應用程式。 若要了解如何使用 C++/WinRT 撰寫非同步應用程式，請參閱透過 C++/WinRT 的並行和非同步作業。 若要了解如何使用 C++/CX 撰寫非同步的應用程式，請參閱 C++/CX 的非同步程式設計。

• 了解如何取得想要讀取、寫入或進行兩者的檔案

  您可以了解如何使用 [開啟檔案和資料夾與選擇器] 中的檔案選擇器來取得檔案。

正在建立檔案

以下說明如何在應用程式的本機資料夾中建立檔案。 若已存在，我們會加以取代。

// Create sample file; replace if exists.
Windows.Storage.StorageFolder storageFolder =
    Windows.Storage.ApplicationData.Current.LocalFolder;
Windows.Storage.StorageFile sampleFile =
    await storageFolder.CreateFileAsync("sample.txt",
        Windows.Storage.CreationCollisionOption.ReplaceExisting);

// MainPage.h
#include <winrt/Windows.Storage.h>
...
Windows::Foundation::IAsyncAction ExampleCoroutineAsync()
{
    // Create a sample file; replace if exists.
    Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
    co_await storageFolder.CreateFileAsync(L"sample.txt", Windows::Storage::CreationCollisionOption::ReplaceExisting);
}

// Create a sample file; replace if exists.
StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
concurrency::create_task(storageFolder->CreateFileAsync("sample.txt", CreationCollisionOption::ReplaceExisting));

' Create sample file; replace if exists.
Dim storageFolder As StorageFolder = Windows.Storage.ApplicationData.Current.LocalFolder
Dim sampleFile As StorageFile = Await storageFolder.CreateFileAsync("sample.txt", CreationCollisionOption.ReplaceExisting)

寫入檔案

以下說明如何使用 StorageFile 類別寫入磁碟上的可寫入檔案。 寫入檔案之每個方式的常見第一個步驟（除非您在建立檔案之後立即寫入檔案），就是使用 StorageFolder.GetFileAsync 取得檔案。

Windows.Storage.StorageFolder storageFolder =
    Windows.Storage.ApplicationData.Current.LocalFolder;
Windows.Storage.StorageFile sampleFile =
    await storageFolder.GetFileAsync("sample.txt");

// MainPage.h
#include <winrt/Windows.Storage.h>
...
Windows::Foundation::IAsyncAction ExampleCoroutineAsync()
{
    Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
    auto sampleFile{ co_await storageFolder.CreateFileAsync(L"sample.txt", Windows::Storage::CreationCollisionOption::ReplaceExisting) };
    // Process sampleFile
}

StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile) 
{
    // Process file
});

Dim storageFolder As StorageFolder = Windows.Storage.ApplicationData.Current.LocalFolder
Dim sampleFile As StorageFile = Await storageFolder.GetFileAsync("sample.txt")

將文字寫入檔案

呼叫 FileIO.WriteTextAsync方法，將文字寫入您的檔案。

await Windows.Storage.FileIO.WriteTextAsync(sampleFile, "Swift as a shadow");

// MainPage.h
#include <winrt/Windows.Storage.h>
...
Windows::Foundation::IAsyncAction ExampleCoroutineAsync()
{
    Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
    auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
    // Write text to the file.
    co_await Windows::Storage::FileIO::WriteTextAsync(sampleFile, L"Swift as a shadow");
}

StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile) 
{
    //Write text to a file
    create_task(FileIO::WriteTextAsync(sampleFile, "Swift as a shadow"));
});

Await Windows.Storage.FileIO.WriteTextAsync(sampleFile, "Swift as a shadow")

使用緩衝區將位元組寫入檔案 (2 個步驟)

1. 首先，呼叫 CryptographicBuffer.ConvertStringToBinary以取得您要寫入檔案的位元組緩衝區 (根據字串)。

   var buffer = Windows.Security.Cryptography.CryptographicBuffer.ConvertStringToBinary(
       "What fools these mortals be", Windows.Security.Cryptography.BinaryStringEncoding.Utf8);
   

   // MainPage.h
   #include <winrt/Windows.Security.Cryptography.h>
   #include <winrt/Windows.Storage.h>
   #include <winrt/Windows.Storage.Streams.h>
   ...
   Windows::Foundation::IAsyncAction ExampleCoroutineAsync()
   {
       Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
       auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
       // Create the buffer.
       Windows::Storage::Streams::IBuffer buffer{
           Windows::Security::Cryptography::CryptographicBuffer::ConvertStringToBinary(
               L"What fools these mortals be", Windows::Security::Cryptography::BinaryStringEncoding::Utf8)};
       // The code in step 2 goes here.
   }
   

   StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
   create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
   {
       // Create the buffer
       IBuffer^ buffer = CryptographicBuffer::ConvertStringToBinary
       ("What fools these mortals be", BinaryStringEncoding::Utf8);
   });
   

   Dim buffer = Windows.Security.Cryptography.CryptographicBuffer.ConvertStringToBinary(
       "What fools these mortals be",
       Windows.Security.Cryptography.BinaryStringEncoding.Utf8)
   

2. 然後呼叫 FileIO.WriteBufferAsync 方法，將緩衝區的位元組寫入您的檔案。

   await Windows.Storage.FileIO.WriteBufferAsync(sampleFile, buffer);
   

   co_await Windows::Storage::FileIO::WriteBufferAsync(sampleFile, buffer);
   

   StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
   create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
   {
       // Create the buffer
       IBuffer^ buffer = CryptographicBuffer::ConvertStringToBinary
       ("What fools these mortals be", BinaryStringEncoding::Utf8);      
       // Write bytes to a file using a buffer
       create_task(FileIO::WriteBufferAsync(sampleFile, buffer));
   });
   

   Await Windows.Storage.FileIO.WriteBufferAsync(sampleFile, buffer)
   

使用串流將文字寫入檔案 (4 個步驟)

1. 首先，呼叫 storageFile.OpenAsync 方法來開啟檔案。 當開啟的作業完成時，它會傳回檔案內容的資料流程。

   var stream = await sampleFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
   

   // MainPage.h
   #include <winrt/Windows.Storage.h>
   #include <winrt/Windows.Storage.Streams.h>
   ...
   Windows::Foundation::IAsyncAction ExampleCoroutineAsync()
   {
       Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
       auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
       Windows::Storage::Streams::IRandomAccessStream stream{ co_await sampleFile.OpenAsync(Windows::Storage::FileAccessMode::ReadWrite) };
       // The code in step 2 goes here.
   }
   

   StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
   create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
   {
       create_task(sampleFile->OpenAsync(FileAccessMode::ReadWrite)).then([sampleFile](IRandomAccessStream^ stream)
       {
           // Process stream
       });
   });
   

   Dim stream = Await sampleFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite)
   

2. 接著從 stream 呼叫 IRandomAccessStream.GetOutputStreamAt 方法，以取得輸出資料流。 如果您使用 C#，則它放入 using 陳述式中以管理輸出資料流的存留期。 如果您使用 C++/WinRT，將它放入區塊中，或在使用完畢時將它設為 nullptr，即可控制其存留期。

   using (var outputStream = stream.GetOutputStreamAt(0))
   {
       // We'll add more code here in the next step.
   }
   stream.Dispose(); // Or use the stream variable (see previous code snippet) with a using statement as well.
   

   Windows::Storage::Streams::IOutputStream outputStream{ stream.GetOutputStreamAt(0) };
   // The code in step 3 goes here.
   

   // Add to "Process stream" in part 1
   IOutputStream^ outputStream = stream->GetOutputStreamAt(0);
   

   Using outputStream = stream.GetOutputStreamAt(0)
   ' We'll add more code here in the next step.
   End Using
   

3. 現在，新增此程式碼 (如果您使用 C#，則在現有的 using 陳述式內) 來寫入輸出資料流，方法是建立新的 DataWriter 物件並呼叫 DataWriter.WriteString 方法。

   using (var dataWriter = new Windows.Storage.Streams.DataWriter(outputStream))
   {
       dataWriter.WriteString("DataWriter has methods to write to various types, such as DataTimeOffset.");
   }
   

   Windows::Storage::Streams::DataWriter dataWriter;
   dataWriter.WriteString(L"DataWriter has methods to write to various types, such as DataTimeOffset.");
   // The code in step 4 goes here.
   

   // Added after code from part 2
   DataWriter^ dataWriter = ref new DataWriter(outputStream);
   dataWriter->WriteString("DataWriter has methods to write to various types, such as DataTimeOffset.");
   

   Dim dataWriter As New DataWriter(outputStream)
   dataWriter.WriteString("DataWriter has methods to write to various types, such as DataTimeOffset.")
   

4. 最後，新增此程式碼 (如果您使用 C#，則在內部 using 陳述式內) 以使用 DataWriter.StoreAsync 將文字儲存至您的檔案，以及使用 IOutputStream.FlushAsync關閉資料流。

   await dataWriter.StoreAsync();
   await outputStream.FlushAsync();
   

   dataWriter.StoreAsync();
   outputStream.FlushAsync();
   

   // Added after code from part 3
   dataWriter->StoreAsync();
   outputStream->FlushAsync();
   

   Await dataWriter.StoreAsync()
   Await outputStream.FlushAsync()
   

寫入檔案的最佳做法

如需其他詳細資料和最佳做法指引，請參閱寫入檔案的最佳做法。

從檔案讀取

以下說明如何使用 StorageFile 類別從磁碟上的檔案讀取。 每個從檔案讀取方式的常見第一個步驟是使用 StorageFolder.GetFileAsync 取得檔案。

Windows.Storage.StorageFolder storageFolder =
    Windows.Storage.ApplicationData.Current.LocalFolder;
Windows.Storage.StorageFile sampleFile =
    await storageFolder.GetFileAsync("sample.txt");

Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
// Process file

StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
{
    // Process file
});

Dim storageFolder As StorageFolder = Windows.Storage.ApplicationData.Current.LocalFolder
Dim sampleFile As StorageFile = Await storageFolder.GetFileAsync("sample.txt")

從檔案讀取文字

呼叫 FileIO.ReadTextAsync 方法，即可從檔案讀取文字。

string text = await Windows.Storage.FileIO.ReadTextAsync(sampleFile);

Windows::Foundation::IAsyncOperation<winrt::hstring> ExampleCoroutineAsync()
{
    Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
    auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
    co_return co_await Windows::Storage::FileIO::ReadTextAsync(sampleFile);
}

StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
{
    return FileIO::ReadTextAsync(sampleFile);
});

Dim text As String = Await Windows.Storage.FileIO.ReadTextAsync(sampleFile)

使用緩衝區從檔案讀取文字 (2 個步驟)

1. 首先，呼叫 FileIO.ReadBufferAsync 方法。

   var buffer = await Windows.Storage.FileIO.ReadBufferAsync(sampleFile);
   

   Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
   auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
   Windows::Storage::Streams::IBuffer buffer{ co_await Windows::Storage::FileIO::ReadBufferAsync(sampleFile) };
   // The code in step 2 goes here.
   

   StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
   create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
   {
       return FileIO::ReadBufferAsync(sampleFile);
   
   }).then([](Streams::IBuffer^ buffer)
   {
       // Process buffer
   });
   

   Dim buffer = Await Windows.Storage.FileIO.ReadBufferAsync(sampleFile)
   

2. 然後使用 DataReader 物件，先讀取緩衝區的長度，然後讀取其內容。

   using (var dataReader = Windows.Storage.Streams.DataReader.FromBuffer(buffer))
   {
       string text = dataReader.ReadString(buffer.Length);
   }
   

   auto dataReader{ Windows::Storage::Streams::DataReader::FromBuffer(buffer) };
   winrt::hstring bufferText{ dataReader.ReadString(buffer.Length()) };
   

   // Add to "Process buffer" section from part 1
   auto dataReader = DataReader::FromBuffer(buffer);
   String^ bufferText = dataReader->ReadString(buffer->Length);
   

   Dim dataReader As DataReader = Windows.Storage.Streams.DataReader.FromBuffer(buffer)
   Dim text As String = dataReader.ReadString(buffer.Length)
   

使用串流從檔案讀取文字 (4 個步驟)

1. 呼叫 storageFile.OpenAsync 方法，以開啟檔案的資料流程。 作業完成時，它會傳回檔案內容的資料流程。

   var stream = await sampleFile.OpenAsync(Windows.Storage.FileAccessMode.Read);
   

   Windows::Storage::StorageFolder storageFolder{ Windows::Storage::ApplicationData::Current().LocalFolder() };
   auto sampleFile{ co_await storageFolder.GetFileAsync(L"sample.txt") };
   Windows::Storage::Streams::IRandomAccessStream stream{ co_await sampleFile.OpenAsync(Windows::Storage::FileAccessMode::Read) };
   // The code in step 2 goes here.
   

   StorageFolder^ storageFolder = ApplicationData::Current->LocalFolder;
   create_task(storageFolder->GetFileAsync("sample.txt")).then([](StorageFile^ sampleFile)
   {
       create_task(sampleFile->OpenAsync(FileAccessMode::Read)).then([sampleFile](IRandomAccessStream^ stream)
       {
           // Process stream
       });
   });
   

   Dim stream = Await sampleFile.OpenAsync(Windows.Storage.FileAccessMode.Read)
   

2. 取得稍後要使用的資料流程大小。

   ulong size = stream.Size;
   

   uint64_t size{ stream.Size() };
   // The code in step 3 goes here.
   

   // Add to "Process stream" from part 1
   UINT64 size = stream->Size;
   

   Dim size = stream.Size
   

3. 呼叫 IRandomAccessStream.GetInputStreamAt 方法，以取得輸入資料流。 將此放在 using 陳述式中，以管理資料流程的存留期。 當您呼叫 GetInputStreamAt 以將位置設定為資料流開頭時，請指定 0。

   using (var inputStream = stream.GetInputStreamAt(0))
   {
       // We'll add more code here in the next step.
   }
   

   Windows::Storage::Streams::IInputStream inputStream{ stream.GetInputStreamAt(0) };
   Windows::Storage::Streams::DataReader dataReader{ inputStream };
   // The code in step 4 goes here.
   

   // Add after code from part 2
   IInputStream^ inputStream = stream->GetInputStreamAt(0);
   auto dataReader = ref new DataReader(inputStream);
   

   Using inputStream = stream.GetInputStreamAt(0)
   ' We'll add more code here in the next step.
   End Using
   

4. 最後，在現有的 using 陳述式中新增此程式碼，以取得資料流上的 DataReader 物件，然後藉由呼叫DataReader.LoadAsync 和 DataReader.ReadString 來讀取文字。

   using (var dataReader = new Windows.Storage.Streams.DataReader(inputStream))
   {
       uint numBytesLoaded = await dataReader.LoadAsync((uint)size);
       string text = dataReader.ReadString(numBytesLoaded);
   }
   

   unsigned int cBytesLoaded{ co_await dataReader.LoadAsync(size) };
   winrt::hstring streamText{ dataReader.ReadString(cBytesLoaded) };
   

   // Add after code from part 3
   create_task(dataReader->LoadAsync(size)).then([sampleFile, dataReader](unsigned int numBytesLoaded)
   {
       String^ streamText = dataReader->ReadString(numBytesLoaded);
   });
   

   Dim dataReader As New DataReader(inputStream)
   Dim numBytesLoaded As UInteger = Await dataReader.LoadAsync(CUInt(size))
   Dim text As String = dataReader.ReadString(numBytesLoaded)
   

另請參閱

• 寫入檔案的最佳做法