如何允许用户只编辑当前行而不编辑文本框上方的前几行

Question

Here is a picture of when I run the program. I want the user to be able to only type on the current line. They shouldn't be able to edit the lines above.

Here is the link to the github if you want to downlaod it to use it for yourself. https://github.com/TeddyRoche/Calculator

Here is the code that is controlling the whole program.

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Data;
 using System.Windows.Documents;
 using System.Windows.Input;
 using System.Windows.Media;
 using System.Windows.Media.Animation;
 using System.Windows.Media.Imaging;
 using System.Windows.Navigation;
 using System.Windows.Shapes;

 namespace Calculator
 {
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
    float number_Initial = 0;
    float prev_Answer = 0;
    List<float> number_List = new List<float>();
    List<string> equations = new List<string>();
    bool valid = true;
    int key_Press = 0;
    int maxLines = 0;
    string lastLine = "";

    public MainWindow()
    {
        InitializeComponent();

    }

    private void NumPressedButton(int i)
    {
        if (valid == false)
        {
            MessageBox.Show("Please enter only numbers.");
            displayText.Text = displayText.Text.Remove(displayText.Text.Length - 1);
        }
        else
        {
            if (key_Press < 12)
            {
                this.displayText.Text += i;
                number_Initial = number_Initial * 10 + i;
                key_Press++;
            }
        }
        valid = true;
    }
    
    private void NumPressedKeyboard(int i)
    {
        if (valid == false)
        {
            MessageBox.Show("Please enter only numbers.");
            displayText.Text = displayText.Text.Remove(displayText.Text.Length - 1);
        }
        else
        {
            if (key_Press < 12)
            {
                number_Initial = number_Initial * 10 + i;
                key_Press++;
            }
        }
        valid = true;
    }
    
    private void OutputSymbol(string x)
    {
        switch (x)
        {
            case "+":
                equations.Add("add");
                break;
            case "-":
                equations.Add("sub");
                break;
            case "*":
                equations.Add("mul");
                break;
            case "/":
                equations.Add("div");
                break;
        }
    }

    private void SymbolPressedButton(String x)
    {
        if (lastLine == "")
        {
            this.displayText.AppendText("Ans");
            number_List.Add(prev_Answer);
            this.displayText.AppendText(x);
            OutputSymbol(x);
            key_Press = key_Press + 4;
        }
        else
        {
            if (number_Initial == 0)
            {
                this.displayText.AppendText(x);
                OutputSymbol(x);
                key_Press++;
            }
            else
            {
                number_List.Add(number_Initial);
                this.displayText.AppendText(x);
                OutputSymbol(x);
                number_Initial = 0;
                key_Press++;
            }
        }
    }

    private void SymbolPressedKeyboard(String x)
    {
        if (lastLine == "")
        {
            this.displayText.AppendText("Ans");
            number_List.Add(prev_Answer);
            OutputSymbol(x);
            key_Press = key_Press + 4;
        }
        else
        {
            if (number_Initial == 0)
            {
                OutputSymbol(x);
                key_Press++;
            }
            else
            {
                number_List.Add(number_Initial);
                OutputSymbol(x);
                number_Initial = 0;
                key_Press++;
            }
        }
    }

    //Display____________________________________________________________________________________________________________________________________________________
    private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        maxLines = displayText.LineCount;
        if(maxLines > 0)
        {
            lastLine = displayText.GetLineText(maxLines - 1);
        }
    }
    
    private void TextBox_KeyDown(object sender, KeyEventArgs e)
    {
        //check to see if what the user presses is a number or one of the appropriate symbols allowed
        //if not sets valid to false
        valid = true;
        if(e.Key < Key.D0 || e.Key > Key.D9)
        {
            if(e.Key < Key.NumPad0 || e.Key > Key.NumPad9)
            {
                valid = false;
               if (e.Key == Key.Add || e.Key == Key.Subtract || e.Key == Key.Multiply || e.Key == Key.Divide || e.Key == Key.Enter)
                {   
                        valid = true;
                }
            }
        }
        if(valid == true)
        {
            //Performing functions when a certain key is pressed
            switch (e.Key)
            {
                case Key.NumPad0:
                case Key.D0:
                    NumPressedKeyboard(0);
                    break;
                case Key.NumPad1:
                case Key.D1:
                    NumPressedKeyboard(1);
                    break;
                case Key.NumPad2:
                case Key.D2:
                    NumPressedKeyboard(2);
                    break;
                case Key.NumPad3:
                case Key.D3:
                    NumPressedKeyboard(3);
                    break;
                case Key.NumPad4:
                case Key.D4:
                    NumPressedKeyboard(4);
                    break;
                case Key.NumPad5:
                case Key.D5:
                    NumPressedKeyboard(5);
                    break;
                case Key.NumPad6:
                case Key.D6:
                    NumPressedKeyboard(6);
                    break;
                case Key.NumPad7:
                case Key.D7:
                    NumPressedKeyboard(7);
                    break;
                case Key.NumPad8:
                case Key.D8:
                    NumPressedKeyboard(8);
                    break;
                case Key.NumPad9:
                case Key.D9:
                    NumPressedKeyboard(9);
                    break;
                case Key.Add:
                    SymbolPressedKeyboard("+");
                    break;
                case Key.Subtract:
                    SymbolPressedKeyboard("-");
                    break;
                case Key.Divide:
                    SymbolPressedKeyboard("/");
                    break;
                case Key.Multiply:
                    SymbolPressedKeyboard("*");
                    break;
                case Key.Enter:
                    Equals_Equation();
                    break;
            }
        }
        else if(valid == false)
        {
            MessageBox.Show("Please enter only numbers.");
            //displayText.Text = displayText.Text.Remove(displayText.Text.Length - 1);
        }
    }
    //Display____________________________________________________________________________________________________________________________________________________


    //Numbers ___________________________________________________________________________________________________________________________________________________
    private void _0_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(0);
    }

    private void _1_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(1);
    }

    private void _2_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(2);
    }

    private void _3_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(3);
    }

    private void _4_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(4);
    }

    private void _5_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(5);
    }

    private void _6_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(6);
    }

    private void _7_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(7);
    }

    private void _8_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(8);
    }

    private void _9_Click(object sender, RoutedEventArgs e)
    {
        NumPressedButton(9);
    }
    //Numbers____________________________________________________________________________________________________________________________________________________


    //Equations__________________________________________________________________________________________________________________________________________________
    private void Divide_Click(object sender, RoutedEventArgs e)
    {
        SymbolPressedButton("/");

    }

    private void Multiply_Click(object sender, RoutedEventArgs e)
    {
        SymbolPressedButton("*");

    }

    private void Subtract_Click(object sender, RoutedEventArgs e)
    {
        SymbolPressedButton("-");

    }

    private void Add__Click(object sender, RoutedEventArgs e)
    {
        SymbolPressedButton("+");
    }
    
    protected void Equals_Equation()
    {
        if(equations.Count != 0)
        {
            if(this.displayText.Text.StartsWith("1") || this.displayText.Text.StartsWith("2") || this.displayText.Text.StartsWith("3") || this.displayText.Text.StartsWith("4") || this.displayText.Text.StartsWith("5") || this.displayText.Text.StartsWith("6") || this.displayText.Text.StartsWith("7") || this.displayText.Text.StartsWith("8") || this.displayText.Text.StartsWith("9") || this.displayText.Text.StartsWith("0"))
            {
                number_List.Add(number_Initial);
                this.displayText.AppendText("\n");
                //loop that goes through the equations list and does the appropriate calculations
                //Does Multiplication and Division first
                for (int s = 0; s < equations.Count(); s++)
                {
                    if (equations[s] == "mul")
                    {
                        number_List[s] = number_List[s] * number_List[s + 1];
                    }
                    else if (equations[s] == "div")
                    {
                        number_List[s] = number_List[s] / number_List[s + 1];
                    }
                }
                //Then does Addition and Subtraction next
                for (int s = 0; s < equations.Count(); s++)
                {
                    if (equations[s] == "add")
                    {
                        number_List[0] = number_List[0] + number_List[s + 1];
                    }
                    else if (equations[s] == "sub")
                    {
                        number_List[0] = number_List[0] - number_List[s + 1];
                    }
                }
                //changes the display to show the answer and creates a new line for the user to continue
                this.displayText.Text += number_List[0];
                number_Initial = number_List[0];
                number_List.Clear();
                prev_Answer = number_Initial;
                //number_List.Add(number_Initial);
                number_Initial = 0;
                equations.Clear();
                this.displayText.AppendText("\n");
                this.displayText.PageDown();
                displayText.Select(displayText.Text.Length, 0);
            }
            else if (this.displayText.Text.StartsWith("A"))
            {
                number_List.Insert(0, prev_Answer);
                number_List.Add(number_Initial);
                this.displayText.AppendText("\n");
                //loop that goes through the equations list and does the appropriate calculations
                //Does Multiplication and Division first
                for (int s = 0; s < equations.Count(); s++)
                {
                    if (equations[s] == "mul")
                    {
                        number_List[s] = number_List[s] * number_List[s + 1];
                    }
                    else if (equations[s] == "div")
                    {
                        number_List[s] = number_List[s] / number_List[s + 1];
                    }
                }
                //Then does Addition and Subtraction next
                for (int s = 0; s < equations.Count(); s++)
                {
                    if (equations[s] == "add")
                    {
                        number_List[0] = number_List[0] + number_List[s + 1];
                    }
                    else if (equations[s] == "sub")
                    {
                        number_List[0] = number_List[0] - number_List[s + 1];
                    }
                }
                //changes the display to show the answer and creates a new line for the user to continue
                this.displayText.Text += number_List[0];
                number_Initial = number_List[0];
                number_List.Clear();
                prev_Answer = number_Initial;
                //number_List.Add(number_Initial);
                number_Initial = 0;
                equations.Clear();
                this.displayText.AppendText("\n");
                this.displayText.PageDown();
                displayText.Select(displayText.Text.Length, 0);
            }
        }
        else
        {

        }
        key_Press = 0;
    }
    
    private void Equals_Click(object sender, RoutedEventArgs e)
    {
        Equals_Equation();
    }

    //Clears all stored data so the user can start from scratch
    private void Clear_Click(object sender, RoutedEventArgs e)
    {
        number_List.Clear();
        number_Initial = 0;
        equations.Clear();
        this.displayText.Clear();
        key_Press = 0;
    }
    
    //Equations__________________________________________________________________________________________________________________________________________________

}

}

I havent found much that has helped with only allowing the user to edit the current line. I see a lot with not allowing the user to edit the whole textBox.

I want the user to only be able to edit the current line. Right know I can use the arrow keys or click with my mouse on the previous lines and can edit them and I dont want them to be allowed to do this.

Answer 1

Here is a quick example. Hopefully this gives you enough info.

XAML

<TextBox
  AcceptsReturn="True"
  TextWrapping="Wrap"
  VerticalScrollBarVisibility="Auto" 
  PreviewTextInput="TextBox_PreviewTextInput"/>

Code Behind

private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
   if (sender is not TextBox box) //semi-redundant safety check
     return;
    
   //make sure there is text, also make sure there is a newline in the box
   if (string.IsNullOrEmpty(box.Text) || (!box.Text.Contains('\n') && !box.Text.Contains('\r')))
     return;
   
   //through some testing I found the \r would be there without a \n so I include both for completeness
   var lastReturn = Math.Max(box.Text.LastIndexOf('\r'), box.Text.LastIndexOf('\n'));
   if (box.CaretIndex <= lastReturn)
     e.Handled = true;
}

This solution can be expanded on, but it mainly prevents the Text from changing whenever Text is entered on any line but the last. I like it as you can also move the Text Caret around to get standard functionality still (highlighting, selection, etc.)