如何：從字串中讀取字元

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下列程式碼範例會示範如何以同步或非同步的方式，從字串讀取字元。

範例：以同步方式讀取字元

此範例會以同步方式，從字串讀取 13 個字元、將其儲存在陣列中，然後顯示它們。 接著讀取字串中剩餘的字元、從陣列的第六個元素開始儲存這些字元，然後顯示陣列的內容。

using System;
using System.IO;

public class CharsFromStr
{
    public static void Main()
    {
        string str = "Some number of characters";
        char[] b = new char[str.Length];

        using (StringReader sr = new StringReader(str))
        {
            // Read 13 characters from the string into the array.
            sr.Read(b, 0, 13);
            Console.WriteLine(b);

            // Read the rest of the string starting at the current string position.
            // Put in the array starting at the 6th array member.
            sr.Read(b, 5, str.Length - 13);
            Console.WriteLine(b);
        }
    }
}
// The example has the following output:
//
// Some number o
// Some f characters

Imports System.IO

Public Class CharsFromStr
    Public Shared Sub Main()
        Dim str As String = "Some number of characters"
        Dim b(str.Length - 1) As Char

        Using sr As StringReader = New StringReader(str)
            ' Read 13 characters from the string into the array.
            sr.Read(b, 0, 13)
            Console.WriteLine(b)

            ' Read the rest of the string starting at the current string position.
            ' Put in the array starting at the 6th array member.
            sr.Read(b, 5, str.Length - 13)
            Console.WriteLine(b)
        End Using
    End Sub
End Class
' The example has the following output:
'
' Some number o
' Some f characters

範例：以非同步方式讀取字元

下一個範例是 WPF 應用程式背後的程式碼。 在載入視窗時，此範例會以非同步方式，從 TextBox 控制項讀取所有字元，然後將其儲存在陣列中。 接著會以非同步方式將每個字母或空格字元寫入 TextBlock 控制項的個別行。

using System;
using System.Text;
using System.Windows;
using System.IO;

namespace StringReaderWriter
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void Window_Loaded(object sender, RoutedEventArgs e)
        {
            char[] charsRead = new char[UserInput.Text.Length];
            using (StringReader reader = new StringReader(UserInput.Text))
            {
                await reader.ReadAsync(charsRead, 0, UserInput.Text.Length);
            }

            StringBuilder reformattedText = new StringBuilder();
            using (StringWriter writer = new StringWriter(reformattedText))
            {
                foreach (char c in charsRead)
                {
                    if (char.IsLetter(c) || char.IsWhiteSpace(c))
                    {
                        await writer.WriteLineAsync(char.ToLower(c));
                    }
                }
            }
            Result.Text = reformattedText.ToString();
        }
    }
}

Imports System.IO
Imports System.Text

''' <summary>
''' Interaction logic for MainWindow.xaml
''' </summary>

Partial Public Class MainWindow
    Inherits Window
    Public Sub New()
        InitializeComponent()
    End Sub
    Private Async Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
        Dim charsRead As Char() = New Char(UserInput.Text.Length) {}
        Using reader As StringReader = New StringReader(UserInput.Text)
            Await reader.ReadAsync(charsRead, 0, UserInput.Text.Length)
        End Using

        Dim reformattedText As StringBuilder = New StringBuilder()
        Using writer As StringWriter = New StringWriter(reformattedText)
            For Each c As Char In charsRead
                If Char.IsLetter(c) Or Char.IsWhiteSpace(c) Then
                    Await writer.WriteLineAsync(Char.ToLower(c))
                End If
            Next
        End Using
        Result.Text = reformattedText.ToString()
    End Sub
End Class

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