Enable disable button on text changed in c# winform

问题

I am developing an application, in which there is a button in search box (like one in itunes). I want to enable cancel button whenever there is text in text box and disable it when text box is empty. I tried with text_changed event on textbox with the following code, but it jump over the if condition. Even sender sends me correct values but i am unable to put it into if else.

private void textBox1_TextChanged(object sender, EventArgs e)
    {
        if (string.IsNullOrEmpty(sender.ToString()))
        {
            btn_cancel.Visible = false;
        }
        else
        {
            btn_cancel.Visible = true;
        }
    }

Please help

回答1:

Here is a simple solution.

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        this.button1.Enabled = !string.IsNullOrWhiteSpace(this.textBox1.Text);
    }

Of course, you'll have to set the button.Enabled = false when the form initially loads since the textbox event won't fire on startup (true for all answers currently provided for your question).

回答2:

private void textBox1_TextChanged(object sender, EventArgs e)
{
    if (String.IsNullOrEmpty(textBox1.Text))
        btn_cancel.Visible = false;
    else
        btn_cancel.Visible = true;
}

回答3:

Try this:

private void textBox1_TextChanged(object sender, EventArgs e)
{
    var textbox = sender as TextBox;
    if (string.IsNullOrEmpty(textbox.Text))
    {
        btn_cancel.Visible = false;
    }
    else
    {
        btn_cancel.Visible = true;
    }
}

sender.ToString() will always return System.Windows.Forms.TextBox you need to cast sender as TextBox and use the Text value for your null or empty check

回答4:

try casting the sender to TextBox :

if (string.IsNullOrEmpty(((TextBox)sender).Text))

回答5:

One liner:

btn_cancel.Visible = textBox1.Text.Length > 0;

回答6:

This is how I'd do it:

private void textBox1_TextChanged(object sender, EventArgs e)
{        
    string text = ((sender as TextBox) == null ? string.Empty : (sender as TextBox).Text);
    this.button1.Enabled = (string.IsNullOrWhiteSpace(text) == false);
}

This doesn't assume the event source is a specific control and avoids an exception if by mistake it's attached to something that's not a TextBox.

来源：https://stackoverflow.com/questions/14350987/enable-disable-button-on-text-changed-in-c-sharp-winform

标签

winforms