如何避免DataGridView添加重复行？现有代码无效求解决方案

Let's break down the issues in your current code and fix them step by step:

Issues with Your Current Code #

• Index Out-of-Bounds Error: Your loop uses i <= dgvOC.Rows.Count, but DataGridView rows are zero-indexed. This means when i equals Rows.Count, you're trying to access a row that doesn't exist, which will throw an IndexOutOfRangeException.
• Incomplete Logic: You only check for duplicates but don't actually prevent adding a new row when a duplicate is found. Also, you only add a row when the grid is empty—there's no code to add a row if no duplicates are found when the grid has existing rows.
• Null Reference Risk: If dgvOC.Rows[i].Cells[0].Value is null, calling ToString() will crash your app.

Corrected Solution #

Here's a revised version that properly handles duplicate checks, avoids errors, and implements the expected behavior:

// Flag to track if a duplicate product is found
bool duplicateFound = false;

// Iterate through existing rows (use < instead of <= to avoid index errors)
for (int i = 0; i < dgvOC.Rows.Count; i++)
{
    // Skip the new row if your DataGridView allows user to add rows (it has an empty row at the end)
    if (dgvOC.Rows[i].IsNewRow)
        continue;

    // Safely get the product name from the cell, handle null values
    string existingProduct = dgvOC.Rows[i].Cells[0].Value?.ToString() ?? string.Empty;
    string newProduct = txtProd.Text.Trim(); // Trim whitespace to avoid accidental duplicates

    if (string.Equals(existingProduct, newProduct, StringComparison.OrdinalIgnoreCase))
    {
        duplicateFound = true;
        break; // No need to check further once a duplicate is found
    }
}

if (duplicateFound)
{
    MessageBox.Show("Usted ya ha agregado un producto con el mismo nombre. Modifique la cantidad o borre el producto para agregar una nueva entrada.");
}
else
{
    // Add the new row since no duplicates were found
    dgvOC.Rows.Add(txtProd.Text.Trim(), numCant.Value, txtTipo.Text, precioGuardado, precioGuardado * (int)numCant.Value);
}

Key Improvements #

• Safe Indexing: Uses i < dgvOC.Rows.Count to avoid accessing non-existent rows, and skips the IsNewRow if your grid enables user row addition.
• Null Safety: Uses the null-conditional operator (?.) and null-coalescing operator (??) to handle cases where the cell value might be null.
• Case-Insensitive Check: Uses StringComparison.OrdinalIgnoreCase to treat "ProductA" and "producta" as duplicates (remove this if you want case-sensitive checks).
• Proper Flow Control: Sets a flag when a duplicate is found, then either shows a message or adds the new row based on that flag.
• Whitespace Handling: Trims the input product name to prevent duplicates caused by extra spaces.

Bonus: Updating Quantity Instead of Blocking #

If you'd prefer to update the existing product's quantity instead of just blocking the addition, you can modify the loop to find the duplicate row and adjust its value:

bool duplicateFound = false;
int duplicateRowIndex = -1;

for (int i = 0; i < dgvOC.Rows.Count; i++)
{
    if (dgvOC.Rows[i].IsNewRow)
        continue;

    string existingProduct = dgvOC.Rows[i].Cells[0].Value?.ToString() ?? string.Empty;
    string newProduct = txtProd.Text.Trim();

    if (string.Equals(existingProduct, newProduct, StringComparison.OrdinalIgnoreCase))
    {
        duplicateFound = true;
        duplicateRowIndex = i;
        break;
    }
}

if (duplicateFound)
{
    // Get current quantity and add the new quantity
    int currentQuantity = Convert.ToInt32(dgvOC.Rows[duplicateRowIndex].Cells[1].Value);
    int newQuantity = currentQuantity + (int)numCant.Value;

    // Update the quantity and total price cells
    dgvOC.Rows[duplicateRowIndex].Cells[1].Value = newQuantity;
    dgvOC.Rows[duplicateRowIndex].Cells[4].Value = precioGuardado * newQuantity;

    MessageBox.Show("Producto existente encontrado. Cantidad actualizada.");
}
else
{
    dgvOC.Rows.Add(txtProd.Text.Trim(), numCant.Value, txtTipo.Text, precioGuardado, precioGuardado * (int)numCant.Value);
}

This way, users don't have to manually modify existing rows—your app handles updating the quantity automatically!

内容的提问来源于stack exchange，提问作者Newbee4Ever