如何从包含多个相似部分的字符串中仅替换子字符串的一部分？

Question

I might have not stated the question as what I would like to. Please consider below scenario.

Scenario:
I am implementing a Search/Replace functionality in my C# Win Form application. This feature will have the option to replace a substring that "starts with" or "ends with" a certain value. For example:

• A string contains "123ABCD" . Replacing "123" with "XYZ" should produce: "XYZABCD"
• A string contains "ABCD123" . Replacing "123" with "XYZ" should produce: "ABCDXYZ"

Both of these features are working fine. My problem is when the string contains "123ABCD123" . Both operations return the wrong value when using "XYZ" .

• "starts with" produces "XYZABCDXYZ" , instead of "XYZABCD"
• "ends with" produces "XYZABCDXYZ" instead of "ABCDXYZ"

Can anyone give me an idea how to achieve that?

Thanks !!!

Code Snippet:

if (this.rbMatchFieldsStartedWith.Checked)
{
    if (caseSencetive)
    {
        matched = currentCellValue.StartsWith(findWhat);
    }
    else
    {
        matched = currentCellValue.ToLower().StartsWith(findWhat.ToLower());
    }
}
else if (this.rbMatchFieldsEndsWith.Checked)
{
    if (caseSencetive)
    {
        matched = currentCellValue.EndsWith(findWhat);
    }
    else
    {
        matched = currentCellValue.ToLower().EndsWith(findWhat.ToLower());
    }
}

if (matched)
{
    if (replace)
    {
        if (this.rbMatchWholeField.Checked)
        {
            currentCell.Value = replaceWith;
        }
        else
        {
            currentCellValue = currentCellValue.Replace(findWhat, replaceWith);
            currentCell.Value = currentCellValue;
        }
        this.QCGridView.RefreshEdit();
    }
    else
    {
        currentCell.Style.BackColor = Color.Aqua;
    }
}

Answer 1

This sounds like a good one for regular expressions .

It is supported by .NET, and also has a replacement syntax.

Answer 2

Implement the replacement method dependent on the search mode.

Replace the line

currentCellValue = currentCellValue.Replace(findWhat, replaceWith);

with

if (this.rbMatchFieldsStartedWith.Checked)
{
    // target string starts with findWhat, so remove findWhat and prepend replaceWith
    currentCellValue = replaceWith + currentCellValue.SubString(findWhat.Length);
}
else
{
    // target string end with findWhat, so remove findWhat and append replaceWith.
    currentCellValue = currentCellValue.SubString(0, currentCellValue.Length - findWhat.Length) + replaceWith;
}

currentCell.Value = newValue;

Answer 3

I just want to try a replacement method without using regex.
(Regex could be the right way to do it, but it was funny to find an alternative)

void Main()
{
    string test = "123ABCD123";  // String to change
    string rep = "XYZ";          // String to replace
    string find = "123";         // Replacement string
    bool searchStart = true;     // Flag for checkbox startswith 
    bool searchEnd = true;       // Flag for checkbox endswith
    bool caseInsensitive = true; // Flag for case type replacement

    string result = test;         
    int pos = -1;
    int lastPos = -1;

    if(caseInsensitive == true)
    {
        pos = test.IndexOf(find, StringComparison.InvariantCultureIgnoreCase);
        lastPos = test.LastIndexOf(find, StringComparison.InvariantCultureIgnoreCase);
    }
    else
    {
        pos = test.IndexOf(find, StringComparison.Ordinal);
        lastPos = test.LastIndexOf(find, StringComparison.Ordinal);
    }

    result = test;
    if(pos == 0 && searchStart == true)
    {
        result = rep + test.Substring(find.Length);
    }
    if(lastPos != 0 && lastPos != pos && lastPos + find.Length == test.Length && searchEnd == true)
    {
        result = result.Substring(0, lastPos) + rep;
    }
    Console.WriteLine(result);
}

Answer 4

First off all let's trace your scenario assuming:

• string to work on is 123ABCD123
• starts with is checked.
• aim is to replace "123" with "XYZ"

by just reading your code. We hit if (this.rbMatchFieldsStartedWith.Checked) and which evaluates to true. So we step in that block. We hit matched = currentCellValue.StartsWith(findWhat); and matched = true . We continue with if (matched) condition which also evaluates to true . After that if (replace) evaluates to true . Finally we make the last decision with if (this.rbMatchWholeField.Checked) which evaluates to false so we continue with else block:

currentCellValue = currentCellValue.Replace(findWhat, replaceWith);
currentCell.Value = currentCellValue;

First line in this block replaces all the occurrences of findWhat with replaceWith , namely all the occurrences of 123 with XYZ. Of course this is not the desired behaviour. Instead of Replace you must use a function that replaces just the first or the last occurrence of the string according to the input of course.