緣起
這一篇最終的目的,是希望能夠透過JavaScript來觸發Server端的Function來做一些事情,在這個過程中,我們透過觀察LinkButton的PostBack運作,進而想出如何使用JavaScript利用LinkButton的PostBack來達到這樣的目的。
觀察Button與LinkButton的PostBack動作
首先,在畫面中安排一個TextBox,一個Button,一個LinkButton,以及一個Label
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><asp:Button ID="Button1" runat="server" Text="Button" /><asp:LinkButton ID="LinkButton1" runat="server">LinkButton</asp:LinkButton><br /><asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
接著撰寫後端的Button1與LinkButton1的Click事件
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click Me.Label1.Text = "Button PostBack: " + Me.TextBox1.TextEnd SubProtected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click Me.Label1.Text = "LinkButton PostBack: " + Me.TextBox1.TextEnd Sub
以上是很簡單的範例,執行後就是把TextBox中輸入的內容,加上一些文字,顯示在Label1上。不過我們的重點,是要觀察這樣的內容,會產生什麼樣的HTML與JavaScript在Client端的瀏覽器裡。因此我們在瀏覽器中,去檢視一下原始碼
<!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><title></title></head><body> <form name="form1" method="post" action="Default.aspx" id="form1"><div><input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" /><input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" /><input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwUKMTI0MzMyNTQxMw9kFgICAw9kFgICBw8PFgIeBFRleHQFGExpbmtCdXR0b24gUG9zdEJhY2s6IGFhYWRkZG/Mw6b4JgMDyr44Wysx+J+xFb4r" /></div><script type="text/javascript">//<![CDATA[var theForm = document.forms['form1'];if (!theForm) { theForm = document.form1;}function __doPostBack(eventTarget, eventArgument) { if (!theForm.onsubmit || (theForm.onsubmit() != false)) { theForm.__EVENTTARGET.value = eventTarget; theForm.__EVENTARGUMENT.value = eventArgument; theForm.submit(); }}//]]></script><div><input type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" value="/wEWBAKntYX5AwLs0bLrBgKM54rGBgLM9PumD3NI60/Yb7kCeqTjhk8wrZHsWt8U" /></div> <div> <input name="TextBox1" type="text" value="aaa" id="TextBox1" /> <input type="submit" name="Button1" value="Button" id="Button1" /> <a id="LinkButton1" href="javascript:__doPostBack('LinkButton1','')">LinkButton</a> <br /> <span id="Label1">LinkButton PostBack: aaa</span> </div> </form></body></html>
觀察原始碼
我們來觀察一下原始碼,首先可以觀察到,本來在ASPX中的Button與LinkButton分別變為
- Button:<input name="TextBox1" type="text" value="aaa" id="TextBox1" />
- LinkButton:<a id="LinkButton1" href="javascript:__doPostBack('LinkButton1','')">LinkButton</a>
這邊可以看出來,Button變為Submit的按鈕,透過Submit來運作PostBack,這點對於JavaScript要運用上,比較使不上力。不過再來觀察【LinkButton】,他所產生的是一個超連結<a>的Tag,並且透過JavaScript中呼叫【javascript:__doPostBack('LinkButton1','')】,這個如果我要透過JavaScript來模擬她,就很簡單,只要呼叫相同的【__doPostBack】就可以囉。
用Input type=Button利用LinkButton
我們就來是試試看,是否可以透過一個HTML的button來觸發LinkButton的PostBack
因此我們畫面中在安排一個Input type=button
<input id="Button2" type="button" value="我是HTML的button" onclick="__doPostBack('LinkButton1','')" />
接著運作看看。果然跟LinkButton的運作結果是一模一樣的。
加上呼叫字定的Function==>JavaScript呼叫Server端自訂Function
在最後,我們在後端加上一個自訂的Function,然後改寫一下LinkButton的click事件呼叫這個Function,這樣,就可以達到【Client端透過JavaScript呼叫後端自訂Function】的目的囉
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- Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click
- 'Me.Label1.Text = "LinkButton PostBack: " + Me.TextBox1.Text
- Me.Label1.Text = Test("LinkButton PostBack: " + Me.TextBox1.Text)
-
- End Sub
-
- Private Function Test(ByVal str As String) As String
- Return str + ",這是透過自訂Function處理的唷!!"
- End Function
Protected Sub LinkButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LinkButton1.Click 'Me.Label1.Text = "LinkButton PostBack: " + Me.TextBox1.Text Me.Label1.Text = Test("LinkButton PostBack: " + Me.TextBox1.Text)End SubPrivate Function Test(ByVal str As String) As String Return str + ",這是透過自訂Function處理的唷!!"End Function
結論
透過觀察LinkButton所產生的HTML原始碼,就可以大致上瞭解他是怎麼做PostBack,也就可以自己更靈活的去運用他。例如,如果我們要在GridView中,讓每個Row都能夠點選Row的任一位置,就有【選擇(Select) Row】的效果,就可以透過這樣的技巧來達成唷。