.Net Treasure: Call JavaScript From server Side

Calling JavaScript from ASP.NET Master Page and Content Pages - Part I

Calling JavaScript from Master and Content Pages confuses a lot of developers. In this article, we will see some common problems and their solutions of calling JavaScript from a Master/Content page. This article is Part I of the two part series and will cover JavaScript in Master Pages. The next article will cover JavaScript in Content pages.

Update: Part II of this article can be read over here Calling JavaScript from ASP.NET Master Page and Content Pages - Part II

Call JavaScript From Master Page

You can call an existing JavaScript function from a Master Page or can create one on the fly. Here are some common scenarios:

1. Create a JavaScript function on the fly and call the JavaScript function in the MasterPage Page_Load() event

protected void Page_Load(object sender, EventArgs e)

{

string someScript = "";

someScript = "<script language='javascript'>alert('Called from CodeBehind');</script>";

Page.ClientScript.RegisterStartupScript(this.GetType(), "onload", someScript);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim someScript As String = ""

someScript = "<script language='javascript'>alert('Called from CodeBehind');</script>"

Page.ClientScript.RegisterStartupScript(Me.GetType(), "onload", someScript)

End Sub

The Page.ClientScript.RegisterStartupScript() allows you to emit client-side script blocks from code behind. More info can be found over here http://msdn.microsoft.com/en-us/library/system.web.ui.clientscriptmanager.registerstartupscript.aspx

2. Call an existing JavaScript function on MasterPage Page_Load() event

Let us assume you have an existing JavaScript function declared in between the <head> tags, then here’s how to call that function from Page_Load()

function invokeMeMaster() {

alert('I was invoked from Master');

}

</script>

<asp:ContentPlaceHolder id="head" runat="server">

</asp:ContentPlaceHolder>

</head>

protected void Page_Load(object sender, EventArgs e)

{

if (!Page.ClientScript.IsStartupScriptRegistered("alert"))

{

Page.ClientScript.RegisterStartupScript

(this.GetType(), "alert", "invokeMeMaster();", true);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If (Not Page.ClientScript.IsStartupScriptRegistered("alert")) Then

Page.ClientScript.RegisterStartupScript(Me.GetType(), "alert", "invokeMeMaster();", True)

End If

End Sub

3. Call JavaScript function from MasterPage on Button click

If you want to call a JavaScript function on a Button click, then here’s how to do so:

function invokeMeMaster() {

alert('I was invoked from Masterdotnetcurry');

}

</script>

<asp:ContentPlaceHolder id="head" runat="server">

</asp:ContentPlaceHolder>

</head>

In the <body> tag, add a Button and use the OnClientClick to call this function

<asp:Button ID="btnMaster" runat="server" Text="Button" OnClientClick="return invokeMeMaster();"/>

The OnClientClick() is called before the postback occurs. This gives us a place to check for some condition and cancel the submit if the condition is not satisfied. We will see an example in Tip 6.

4. Access a control on the MasterPage using JavaScript

If you have a control on the MasterPage and need to access it using JavaScript, then here’s how to do so. In this sample, we will test the length of the TextBox to see if there are 5 or more letters. If the number of letters is less than 5, the form submit will be cancelled.

Add a TextBox and a Button control in the MasterPage (outside the ContentPlaceHolder) as shown below

<body>

<div>

<asp:Panel ID="panelMaster" GroupingText="MasterPage controls" runat="server">

<asp:TextBox ID="txtMaster" runat="server"></asp:TextBox>

<asp:Button ID="btnMaster" runat="server" Text="Button" OnClientClick="return accessMasterControl();" />

<br />

</asp:Panel>

<asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">

</asp:ContentPlaceHolder>

</div>

</form>

</body>

In the <head> element of the MasterPage, add the following code:

function accessMasterControl() {

if (document.getElementById('<%=txtMaster.ClientID%>').value.length <= 5) {

alert('Minimum 5 characters required')

return false;

}

else { return true;}

}

</script>

<asp:ContentPlaceHolder id="head" runat="server">

</asp:ContentPlaceHolder>

</head>

5. Access a control on the Content Page from a MasterPage using JavaScript

If you have a control on the Content Page which has to be accessed in the MasterPage using JavaScript, then here’s how to do so:

On the Content Page, create a TextBox as shown below :

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

<asp:Panel ID="panelContent" GroupingText="ContentPage Controls" runat="server">

<asp:TextBox ID="txtContent" runat="server"></asp:TextBox>

</asp:Panel>

</asp:Content>

Now access and populate the TextBox ‘txtContent’ from the MasterPage

function accessControlContentPage() {

var txtCont = document.getElementById('<%= Page.Master.FindControl("ContentPlaceHolder1").FindControl("txtContent").ClientID %>');

txtCont.value = "I got populated using Master Page";

}

</script>

<asp:ContentPlaceHolder id="head" runat="server">

</asp:ContentPlaceHolder>

</head>

6. Ask user before submitting the form on a MasterPage

In order to ask the user for a confirmation before submitting the form, you can either use code behind or can use simple mark up as shown below:

Declare a Button control that causes postback and write the following code in MasterPage.master.cs or .vb

protected void Page_Load(object sender, EventArgs e)

{

string myScript = @"<script type='text/javascript'>

function askBeforeSubmit() {

var msg = 'Are you sure?';

return confirm(msg);

}

</script>";

Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "MakeSure", myScript);

form1.Attributes.Add("onsubmit", "return askBeforeSubmit();");

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

Dim myScript As String = "<script type='text/javascript'>" & ControlChars.CrLf & " function askBeforeSubmit() {" & ControlChars.CrLf & " var msg = 'Are you sure?';" & ControlChars.CrLf & " return confirm(msg);" & ControlChars.CrLf & " }" & ControlChars.CrLf & " </script>"

Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "MakeSure", myScript)

form1.Attributes.Add("onsubmit", "return askBeforeSubmit();")

End Sub

If you want to avoid a code-behind approach, you can ask the user for a confirmation by using the OnClientClick() on the Submit button

<asp:Button ID="btnMaster" runat="server" Text="Button"

OnClientClick="return confirm('Are you sure?');"/>

These were some common scenarios and their solutions when using JavaScript on MasterPages. In the next article, we will see how to use JavaScript in Content Pages. Update: Part II of this article can be read over here Calling JavaScript from ASP.NET Master Page and Content Pages - Part II

I hope you liked the article and I thank you for viewing it.

Calling JavaScript from ASP.NET Master Page and Content Pages - Part II

In this article, we will see some common problems and their solutions of calling JavaScript from a Master/Content page. This article is Part II of the series ‘Calling JavaScript from ASP.NET Master Page and Content Pages’ and in this article; we will cover JavaScript in Content Pages.

Call JavaScript from Content Page

Here are some common scenarios of executing JavaScript from a Content Page.

1. Create a JavaScript function on the fly and call the JavaScript function in the Content Page Page_Load() event

protected void Page_Load(object sender, EventArgs e)

{

const string someScript = "alertMe";

if (!ClientScript.IsStartupScriptRegistered(this.GetType(), someScript))

{

ClientScript.RegisterStartupScript(this.GetType(),

someScript, "alert('I was called from Content page!')", true);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim someScript As String = "alertMe"

If (Not ClientScript.IsStartupScriptRegistered(Me.GetType(), someScript)) Then

ClientScript.RegisterStartupScript(Me.GetType(), someScript, "alert('I was called from Content page!')", True)

End If

End Sub

2. Call a JavaScript function declared in a .js file from the Content Page

If you have a .js file and want to call the function from your Content Page, then here’s how to do so.

Let’s create a .js file called TestScript.js and add the following function in the .js file.

function insideJS() {

alert('Inside .js');

}

Assuming that your .js file is kept in a Script folder, reference the file in your MasterPage in the following manner.

...

Now in your Content Page(in our case Default.aspx.cs or .vb), call the JavaScript function on the Page_Load:

protected void Page_Load(object sender, EventArgs e)

{

if (!Master.Page.ClientScript.IsStartupScriptRegistered("alert"))

{

Master.Page.ClientScript.RegisterStartupScript

(this.GetType(), "alert", "insideJS();", true);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

If (Not Master.Page.ClientScript.IsStartupScriptRegistered("alert")) Then

Master.Page.ClientScript.RegisterStartupScript (Me.GetType(), "alert", "insideJS();", True)

End If

End Sub

3. Referencing the .js file from a Content Page instead of the Master page

The approach shown above in Tip 2 works well, however this approach would add a reference to the .js file for every page in the application (since we are adding the .js in the Master Page). If you want to avoid this approach, then remove the reference added to the .js file in Tip 2 in the Master Page. Now add a reference to the .js file from the Content Page using the ‘RegisterClientScriptInclude’ as shown below:

protected void Page_Load(object sender, EventArgs e)

{

Page.ClientScript.RegisterClientScriptInclude("selective", ResolveUrl(@"Scripts\TestScript.js"));

if (!Master.Page.ClientScript.IsStartupScriptRegistered("alert"))

{

Master.Page.ClientScript.RegisterStartupScript

(this.GetType(), "alert", "insideJS();", true);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

Page.ClientScript.RegisterClientScriptInclude("selective", ResolveUrl("Scripts\TestScript.js"))

If (Not Master.Page.ClientScript.IsStartupScriptRegistered("alert")) Then

Master.Page.ClientScript.RegisterStartupScript(Me.GetType(), "alert", "insideJS();", True)

End If

End Sub

Using this approach, we can avoid referencing the .js file for every content page.

Note: This approach adds the JavaScript reference inside the <body>tag of the page.

4. Declare JavaScript inside the Content page and execute it

If you are looking out to declare JavaScript inside the Content Page, then here’s how to do so. Add the following markup inside the Content page (in our case Default.aspx)

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

<asp:Panel ID="panelContent" GroupingText="ContentPage Controls" runat="server">

<asp:TextBox ID="txtContent" runat="server"></asp:TextBox>

<asp:Button ID="btnContent" runat="server" Text="Button" OnClientClick="Populate();" />

</asp:Panel>

function Populate() {

{

document.getElementById('<%=txtContent.ClientID%>').value = "Hi";

}

</script>

</asp:Content>

The markup shown above populates the textbox with some text on a button click.

5. Accessing a Control on the Master Page From a ContentPage using JavaScript

In our previous article, we saw how in Tip 5 To access a control on the ContentPage From a Master Page using JavaScript. In this tip, we will see how to access a control kept on the MasterPage from a ContentPage. Do the following:

We have added a textbox control to the <body> of the MasterPage as shown below:

<body>

<div>

<asp:Panel ID="panelMaster" GroupingText="MasterPage controls" runat="server">

<asp:TextBox ID="txtMaster" runat="server"></asp:TextBox>

<br />

</asp:Panel>

<asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">

</asp:ContentPlaceHolder>

</div>

</form>

</body>

We will now access this TextBox ‘txtMaster’ in the ContentPage using JavaScript

To do so, go to the Content page (Default.aspx) and add the following line below the <Page> directive to register the MasterPage

<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

...

<%@ MasterType VirtualPath="~/MasterPage.master" %>

...

Now in the code behind of Default.aspx.cs or .vb, access the MasterPage control in the following manner

protected void Page_Load(object sender, EventArgs e)

{

TextBox tb = (TextBox)Master.FindControl("txtMaster");

string val = tb.ClientID;

string script = @"<script>

function PopulateMaster() {

document.getElementById('" + val + @"').value = 'Via Content Page. Love dotnetcurry';

}

PopulateMaster();

</script>";

if (!Page.ClientScript.IsStartupScriptRegistered("Mast"))

{

Page.ClientScript.RegisterStartupScript(this.GetType(),

"Mast", script);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

Dim tb As TextBox = CType(Master.FindControl("txtMaster"), TextBox)

Dim val As String = tb.ClientID

Dim script As String = "<script>" & ControlChars.CrLf & " function PopulateMaster() {" & ControlChars.CrLf & " document.getElementById('" & val & "').value = 'Via Content Page. Love dotnetcurry.com'; " & ControlChars.CrLf & " }" & ControlChars.CrLf & " PopulateMaster();" & ControlChars.CrLf & " </script>"

If (Not Page.ClientScript.IsStartupScriptRegistered("Mast")) Then

Page.ClientScript.RegisterStartupScript(Me.GetType(), "Mast", script)

End If

End Sub

Observe how we have used the RegisterStartupScript instead of RegisterClientScriptBlock. The main difference is that the 'RegisterStartupScript' method places the JavaScript at the bottom of the ASP.NET page right before the closing </form> element whereas the 'RegisterClientScriptBlock' method places the JavaScript directly after the opening <form> element in the page. Had we used the 'RegisterClientScriptBlock', the browser would have executed the JavaScript before the text box is on the page. Therefore, the JavaScript would not have been able to find a ‘txtMaster’ and would give a control not found error. Understanding this simple difference between the two methods can save you hours of work!

6. Call JavaScript function from an ASP.NET AJAX enabled Content Page

If your content page is wrapped in an ASP.NET AJAX UpdatePanel, then you cannot use the ClientScript.RegisterStartupScript to call a JavaScript function during a partial-page postback. Instead, use the ScriptManager.RegisterStartupScript() method.

protected void Page_Load(object sender, EventArgs e)

{

System.Text.StringBuilder sb = new System.Text.StringBuilder();

sb.Append(@"<script language='javascript'>");

sb.Append(@"alert('I love dotnetcurry.com');");

sb.Append(@"</script>");

ScriptManager.RegisterStartupScript(this, this.GetType(), "ajax", sb.ToString(), false);

}

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)

Dim sb As New System.Text.StringBuilder()

sb.Append("<script language='javascript'>")

sb.Append("alert('I love dotnetcurry');")

sb.Append("</script>")

ScriptManager.RegisterStartupScript(Me, Me.GetType(), "ajax", sb.ToString(), False)

End Sub

Observe that the last parameter for RegisterStartupScript() is set to 'false'. This means that the <script> tags will not be added automatically. Since we have already inserted the <script> tags while creating the script in the StringBuilder, we do not need to insert them now.

These were some common scenarios and their solutions when using JavaScript on Content Pages. You can read some common scenarios of using JavaScript on Master Pages as well. I hope you liked the article and I thank you for viewing it.

.Net Treasure

Wednesday, April 6, 2011

Call JavaScript From server Side

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