检查 TextBox 是否为空

Question

I have a TextBox. And I want to check if it's empty.

Which way is better

if(TextBox.Text.Length == 0)

or

if(TextBox.Text == '')

?

Answer 1

You should use String.IsNullOrEmpty() to make sure it is neither empty nor null (somehow):

if (String.IsNullOrEmpty(textBox1.Text))
{
    // Do something...
}

More examples here .

For practical purposes you might also consider using String.IsNullOrWhitespace() since a TextBox expecting whitespace as input probably negates any purpose, except in case of, say, letting the user pick a custom separator for stuff.

Answer 2

I think

string.IsNullOrEmpty(TextBox.Text)

or

string.IsNullOrWhiteSpace(TextBox.Text)

are your best options.

Answer 3

If one is in XAML, one can check whether there is text in a TextBox by using IsEmpty off of Text property.

Turns out that it bubbles down to CollectionView.IsEmpty (not on the string property) to provide the answer. This example of a textbox watermark, where two textboxes are displayed (on the editing one and one with the watermark text). Where the style on the second Textbox (watermark one) will bind to the Text on the main textbox and turn on/off accordingly.

<TextBox.Style>
    <Style TargetType="TextBox">
        <Style.Triggers>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding ElementName=tEnterTextTextBox, Path=IsKeyboardFocusWithin}" Value="False" />
                    <Condition Binding="{Binding ElementName=tEnterTextTextBox, Path=Text.IsEmpty}" Value="True" />
                </MultiDataTrigger.Conditions>
                <Setter Property="Visibility" Value="Visible" />
            </MultiDataTrigger>
            <DataTrigger Binding="{Binding ElementName=tEnterTextTextBox, Path=IsKeyboardFocusWithin}" Value="True">
                <Setter Property="Visibility" Value="Hidden" />
            </DataTrigger>
            <DataTrigger Binding="{Binding ElementName=tEnterTextTextBox, Path=Text.IsEmpty}" Value="False">
                <Setter Property="Visibility" Value="Hidden" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</TextBox.Style>

---

• CollectionView.IsEmpty explanation
• Help Text WaterMark to Disappear when user Types in (answer) (this is the full example which I used from the partial answer given above).

Answer 4

Another way:

    if(textBox1.TextLength == 0)
    {
       MessageBox.Show("The texbox is empty!");
    }

Answer 5

You can put that code in the ButtonClick event or any event:

//Array for all or some of the TextBox on the Form
TextBox[] textBox = { txtFName, txtLName, txtBalance };

//foreach loop for check TextBox is empty
foreach (TextBox txt in textBox)
{
    if (string.IsNullOrWhiteSpace(txt.Text))
    {
        MessageBox.Show("The TextBox is empty!");
        break;
    }
}
return;

Answer 6

Farhan answer is the best and I would like to add that if you need to fullfil both conditions adding the OR operator works, like this:

if (string.IsNullOrEmpty(text.Text) || string.IsNullOrWhiteSpace(text.Text))
{
  //Code
}

Note that there is a difference between using string and String

Answer 7

In my opinion the easiest way to check if a textbox is empty + if there are only letters:

public bool isEmpty()
    {
        bool checkString = txtBox.Text.Any(char.IsDigit);

        if (txtBox.Text == string.Empty)
        {
            return false;
        }
        if (checkString == false)
        {
            return false;
        }
        return true;
    }