代码正在运行，但显示错误 [英] Code is working but showing an error

问题描述

我的代码在下面

My Code is below

private void label94_Click(object sender, EventArgs e)
 {
     float total = 0;
     int counter;
     for (counter = 0; counter < (dataGridView2.Rows.Count); counter++)
      {
        if (dataGridView2.Rows[counter].Cells["Price"].Value != null)
          {
             if (dataGridView2.Rows[counter].Cells["Price"].Value.ToString().Length != null)               {
                 total += float.Parse(dataGridView2.Rows[counter].Cells["Price"].Value.ToString());
                    }
                }
            }
            textBox1.Text = total.ToString();
        }

这段代码运行正常但是通过按住粗体文本代码上的光标显示错误。

错误消息： - 表达式的结果总是'true'，因为'int'类型的值永远不会等于'int'类型的'null'。

我不知道为什么这个消息是展示。请有人帮忙。

this code is running properly but showing an error by holding on the cursor on bold text code.
Error Message :- The result of the expression is always 'true' since a value of type 'int' is never equal to 'null' of type 'int?'.
I don't know why this message is showing. Please someone help.

推荐答案

.ToString（）返回一个字符串。



String.Length返回一个整数。



值类型永远不会等于null。所以它就像检查0 == null一样，它永远不会。



如果你想检查列是否为空，你必须在打电话之前这样做.ToString，因为当字段中的空值在尝试调用空的.ToString时会导致空引用异常。

.ToString() returns a string.

String.Length returns an integer.

Value types will never equal null. So its like checking if 0 == null which it never will.

If you want to check if the column is null, you have to do it WAY before you call .ToString, since a null value in the field will cause a null reference exception when it tries to call .ToString on a null.

if (dataGridView2.Rows[counter].Cells["Price"].Value != null &&
    dataGridView2.Rows[counter].Cells["Price"].Value.ToString().Length > 0)

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