Timer Control Overview
The ASP.NET AJAX Timer control performs postbacks at defined intervals.If you use the Timer control with an UpdatePanel control, you can enable partial-page updates at a defined interval.You can also use the Timer control to post the whole page.
Este tópico contém as seções a seguir:
Cenários
Segundo plano
Exemplos de código
Referência de Classe
Timer Control Scenarios
You use the Timer control when you want to do the following:
Periodically update the contents of one or more UpdatePanel controls without refreshing the whole Web page.
Run code on the server every time that a Timer control causes a postback.
Synchronously post the whole Web page to the Web server at defined intervals.
Segundo plano
The Timer control is a server control that embeds a JavaScript component into the Web page.The JavaScript component initiates the postback from the browser when the interval that is defined in the Interval property has elapsed.You set the properties for the Timer control in code that runs on the server and those properties are passed to the JavaScript component.
An instance of the ScriptManager class must be included in the Web page when you use the Timer control.
When a postback was initiated by the Timer control, the Timer control raises the Tick event on the server.You can create an event handler for the Tick event to perform actions when the page is posted to the server.
Set the Interval property to specify how often postbacks will occur, and set the Enabled property to turn the Timer on or off.The Interval property is defined in milliseconds and has a default value of 60,000 milliseconds, or 60 seconds.
.gif "Observação") Observação: |
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Setting the Interval property of a Timer control to a small value can generate significant traffic to the Web server.Use the Timer control to refresh the content only as often as necessary. |
You can include more than one Timer control on a Web page if different UpdatePanel controls must be updated at different intervals.Alternatively, a single instance of the Timer control can be the trigger for more than one UpdatePanel control in a Web page.
Using a Timer Control Inside an UpdatePanel Control
When the Timer control is included inside an UpdatePanel control, the Timer control automatically works as a trigger for the UpdatePanel control.You can override this behavior by setting the ChildrenAsTriggers property of the UpdatePanel control to false.
For Timer controls inside an UpdatePanel control, the JavaScript timing component is re-created only when each postback finishes.Therefore, the timed interval does not start until the page returns from the postback.For instance, if the Interval property is set to 60,000 milliseconds (60 seconds) but the postback takes 3 seconds to complete, the next postback will occur 63 seconds after the previous postback.
The following example shows how to include a Timer control inside an UpdatePanel control.
<asp:ScriptManager id="ScriptManager1" />
<asp:UpdatePanel id="UpdatePanel1"
UpdateMode="Conditional">
<contenttemplate>
<asp:Timer id="Timer1"
Interval="120000"
OnTick="Timer1_Tick">
</asp:Timer>
</contenttemplate>
</asp:UpdatePanel>
Using a Timer Control Outside an UpdatePanel Control
When the Timer control is outside an UpdatePanel control, you must explicitly define the Timer control as a trigger for the UpdatePanel control to be updated.
If the Timer controls is outside an UpdatePanel control, the JavaScript timing component continues to run as the postback is being processed.For example, if the Interval property is set to 60,000 milliseconds (60 seconds) and the postback takes 3 seconds to complete, the next postback will occur 60 seconds after the previous postback.The user will see the refreshed content in the UpdatePanel control for only 57 seconds.
You must set the Interval property to a value that enables one asynchronous postback to complete before the next postback is initiated.If a new postback is initiated while an earlier postback is being processed, the first postback is canceled.
The following example shows how to use the Timer control outside an UpdatePanel control.
<asp:ScriptManager id="ScriptManager1" />
<asp:Timer ID="Timer1" Interval="120000"
OnTick="Timer1_Tick">
</asp:Timer>
<asp:UpdatePanel ID="UpdatePanel1" >
<Triggers>
<asp:AsyncPostBackTrigger ControlID="Timer1"
EventName="Tick" />
</Triggers>
<ContentTemplate>
<asp:Label ID="Label1" ></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>
Exemplos de código
The following example shows an UpdatePanel control that displays a randomly generated stock price and the time that the stock price was generated.By default, the Timer control updates the content in the UpdatePanel every 10 seconds.The user can decide to update the stock price every 10 seconds, every 60 seconds, or not at all.When the user chooses not to update the stock price, the Enabled property is set to false.
<%@ Page Language="VB" AutoEventWireup="true" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" >
<title>Timer Example Page</title>
<script >
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
OriginalTime.Text = DateTime.Now.ToLongTimeString()
End Sub
Protected Sub Timer1_Tick(ByVal sender As Object, ByVal e As EventArgs)
StockPrice.Text = GetStockPrice()
TimeOfPrice.Text = DateTime.Now.ToLongTimeString()
End Sub
Private Function GetStockPrice() As String
Dim randomStockPrice As Double = 50 + New Random().NextDouble()
Return randomStockPrice.ToString("C")
End Function
Protected Sub RadioButton1_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Timer1.Interval = 10000
Timer1.Enabled = True
End Sub
Protected Sub RadioButton2_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Timer1.Interval = 60000
Timer1.Enabled = True
End Sub
Protected Sub RadioButton3_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Timer1.Enabled = False
End Sub
</script>
</head>
<body>
<form id="form1" >
<asp:ScriptManager ID="ScriptManager1" />
<asp:Timer ID="Timer1" OnTick="Timer1_Tick" Interval="10000" />
<asp:UpdatePanel ID="StockPricePanel" UpdateMode="Conditional">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="Timer1" />
</Triggers>
<ContentTemplate>
Stock price is <asp:Label id="StockPrice" ></asp:Label><BR />
as of <asp:Label id="TimeOfPrice" ></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>
<div>
<asp:RadioButton ID="RadioButton1" AutoPostBack="true" GroupName="TimerFrequency" Text="10 seconds" OnCheckedChanged="RadioButton1_CheckedChanged" /><br />
<asp:RadioButton ID="RadioButton2" AutoPostBack="true" GroupName="TimerFrequency" Text="60 seconds" OnCheckedChanged="RadioButton2_CheckedChanged" /><br />
<asp:RadioButton ID="RadioButton3" AutoPostBack="true" GroupName="TimerFrequency" Text="Never" OnCheckedChanged="RadioButton3_CheckedChanged" /><br />
<br />
Page originally created at <asp:Label ID="OriginalTime" ></asp:Label>
</div>
</form>
</body>
</html>
<%@ Page Language="C#" AutoEventWireup="true" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" >
<title>Timer Example Page</title>
<script >
protected void Page_Load(object sender, EventArgs e)
{
OriginalTime.Text = DateTime.Now.ToLongTimeString();
}
protected void Timer1_Tick(object sender, EventArgs e)
{
StockPrice.Text = GetStockPrice();
TimeOfPrice.Text = DateTime.Now.ToLongTimeString();
}
private string GetStockPrice()
{
double randomStockPrice = 50 + new Random().NextDouble();
return randomStockPrice.ToString("C");
}
protected void RadioButton1_CheckedChanged(object sender, EventArgs e)
{
Timer1.Enabled = true;
Timer1.Interval = 10000;
}
protected void RadioButton2_CheckedChanged(object sender, EventArgs e)
{
Timer1.Enabled = true;
Timer1.Interval = 60000;
}
protected void RadioButton3_CheckedChanged(object sender, EventArgs e)
{
Timer1.Enabled = false;
}
</script>
</head>
<body>
<form id="form1" >
<asp:ScriptManager ID="ScriptManager1" />
<asp:Timer ID="Timer1" OnTick="Timer1_Tick" Interval="10000" />
<asp:UpdatePanel ID="StockPricePanel" UpdateMode="Conditional">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="Timer1" />
</Triggers>
<ContentTemplate>
Stock price is <asp:Label id="StockPrice" ></asp:Label><BR />
as of <asp:Label id="TimeOfPrice" ></asp:Label>
<br />
</ContentTemplate>
</asp:UpdatePanel>
<div>
<br />
Update stock price every:<br />
<asp:RadioButton ID="RadioButton1" AutoPostBack="true" GroupName="TimerFrequency" Text="10 seconds" OnCheckedChanged="RadioButton1_CheckedChanged" /><br />
<asp:RadioButton ID="RadioButton2" AutoPostBack="true" GroupName="TimerFrequency" Text="60 seconds" OnCheckedChanged="RadioButton2_CheckedChanged" /><br />
<asp:RadioButton ID="RadioButton3" AutoPostBack="true" GroupName="TimerFrequency" Text="Never" OnCheckedChanged="RadioButton3_CheckedChanged" />
<br />
Page loaded at <asp:Label ID="OriginalTime" ></asp:Label>
</div>
</form>
</body>
</html>
Tutorials
Demonstra Passo a passo: Introdução ao controle Timer
Demonstra Passo a passo: Usando o controle Timer do ASP.NET com vários controles UpdatePanel
Referência de Classe
The key server classes for the Timer control are shown in the following table.
- Timer
Performs asynchronous or synchronous Web page postbacks at a defined interval.