ASP.NET C# 为什么我不能更改网页中文本框中的文本

Question

I have an ASP.NET project with a simple webpage.When I load the page the textbox display "Hello". When I click the "btnUpload" the text goes away. I tried !IsPostBack in the Load_Form function gut the just make the text stay the same.

protected void Page_Load(object sender, EventArgs e)
{   
    TextBox1.Text = "Hello";               
}

protected void btnUpload_Click(object sender, EventArgs e)
{
   TextBox1.Text = "Good Bye";

}

Answer 1

This is because you have not used

if(!IsPostBack) { }

inside Page_load() method

so modify your code as:

protected void Page_Load(object sender, EventArgs e)
{   
    if(!IsPostBack) {
    TextBox1.Text = "Hello";               
    }
}

protected void btnUpload_Click(object sender, EventArgs e)
{
   TextBox1.Text = "Good Bye";
}

Because, you have not used this, thats why, on the postback of button it changes the value to TextBox1.Text = "Good Bye"; but it follows completing the postback with Page_Load() so it changes it again to TextBox1.Text = "Hello"; that's the reason default value of Page_Load() is shown after render.

Answer 2

You have to use the following condition in the Page_Load event handler, not in the Load_Form :

if (!IsPostBack) {
    TextBox1.Text = "Hello";
}

Your button click event handler is ok.

Hope it helps!

Answer 3

Please see below code :

Default.aspx:

<asp:TextBox ID="text1" runat="server"></asp:TextBox>
<asp:Button ID="btn" runat="server" OnClick="btn_Click" />

Make sure aspx page contain same code for button as shown above.