检查TextBox是否为空并返回MessageBox？

如何解决检查TextBox是否为空并返回MessageBox？

| 我发出此语句来检查TextBox是否为空，但MessageBox始终显示 TextBox是否为空。

    private void NextButton_Click(object sender,EventArgs e)
    {
        decimal MarkPoints,x,y;
        x = HoursNumericUpDown.Value;
        y = MarkNumericUpDown.Value;
        MarkPoints = x * y;

        //decimal MarkPoints = (decimal)HoursNumericUpDown.Value * (decimal)HoursNumericUpDown.Value;


        DataGridViewRow dgvRow = new DataGridViewRow();
        DataGridViewTextBoxCell dgvCell =  new DataGridViewTextBoxCell();

        dgvCell = new DataGridViewTextBoxCell();
        dgvCell.Value = MaterialTextBox.Text;
        dgvRow.Cells.Add(dgvCell);

        dgvCell = new DataGridViewTextBoxCell();
        dgvCell.Value = HoursNumericUpDown.Value;
        dgvRow.Cells.Add(dgvCell);

        dgvCell = new DataGridViewTextBoxCell();
        dgvCell.Value = MarkNumericUpDown.Value;
        dgvRow.Cells.Add(dgvCell);

        dgvCell = new DataGridViewTextBoxCell();
        dgvCell.Value = MarkPoints;
        dgvRow.Cells.Add(dgvCell);

        dataGridView1.Rows.Add(dgvRow);

        MaterialTextBox.Clear();
        HoursNumericUpDown.Value = HoursNumericUpDown.Minimum;
        MarkNumericUpDown.Value = MarkNumericUpDown.Minimum;

        if (String.IsNullOrEmpty(MaterialTextBox.Text))
        {
            MessageBox.Show(\"Enter Material Name Please.\",\"Error\",MessageBoxButtons.OK,MessageBoxIcon.Warning);
            //dataGridView1.Rows.Clear();
        }
        else
        {
            /*if (MarkNumericUpDown.Value < 50)
            {
                int index = dataGridView1.Rows.Add();
                dataGridView1.Rows[1].Cells[4].Value = \"F\";
            }
            else if (MarkNumericUpDown.Value > 50 && MarkNumericUpDown.Value <= 64)
            {
                dataGridView1.Rows[index].Cells[4].Value = \"F\";
            }*/

    

解决方法

        请尝试以下条件：

if (string.IsNullOrWhiteSpace(MaterialTextBox.Text)) {
    // Message box
}

这将处理一些仅包含空格字符的字符串，并且您不必处理有时很棘手的字符串相等性     ,        好吧，您正在检查文本框是否为空之前清除文本框

/* !! This clears the textbox BEFORE you check if it\'s empty */
MaterialTextBox.Clear();

HoursNumericUpDown.Value = HoursNumericUpDown.Minimum;
MarkNumericUpDown.Value = MarkNumericUpDown.Minimum;

if (String.IsNullOrEmpty(MaterialTextBox.Text))
{
        MessageBox.Show(\"Enter Material Name Please.\",\"Error\",MessageBoxButtons.OK,MessageBoxIcon.Warning);
            //dataGridView1.Rows.Clear();
}

    ,        使用如下内容：

if (String.IsNullOrEmpty(MaterialTextBox.Text)) 

    ,        尝试执行以下操作

if (String.IsNullOrEmpty(MaterialTextBox.Text) || String.IsNullOrWhiteSpace(MaterialTextBox.Text))
    {
        //do job
    }
    else
    {
        MessageBox.Show(\"Please enter correct path\");
    }

希望能帮助到你     ,        加上@ tjg184所说的内容，您可以做类似...

if (String.IsNullOrEmpty(MaterialTextBox.Text.Trim())) 

...     ,        

if (MaterialTextBox.Text.length==0)
{
message

}