顯示系統日誌(ASP+)

- 中國WEB開發者網絡 (http://www.webasp.net)
-- 技術教程 (http://www.webasp.net/article/)
--- 顯示系統日誌(ASP+) (http://www.webasp.net/article/13/12563.htm)
-- 作者：未知
-- 發佈日期： 2004-08-24
Written by: Christoph Wille
Translated by: Bernhard Spuida
First published: 8/11/2000

Under Windows 2000 (or NT) the Event Log is about the most important source of information for the
administrator because all events that occurred are logged there - from success to catastrophical failure.
And as it is so important, what would be more obvious than to make it accessible via the web?

The Event Viewer should be familiar to nearly everyone (see picture). In this article I will demonstrate
how the list of entries can be emulated very elegantly using ASP.NET and the .NET Framework SDK. As an
exercise for the reader I will leave the construction of a page for the full details of an entry.


The use of the source code in this article requires the Microsoft .NET Framework SDK installed on a
Webserver. I also presume that the reader is familiar to some degree with the C# programming language.

The Brute Force Method
When we have to be quick and dirty, knowledge from the days of ASP can very well be used to generate a
list of events (Even with a table, though this example doesn't do that). The name of the program is the
name of the game: simple.aspx.


<% @Page Language="C#" %>
<% @Import Namespace="System.Diagnostics" %>
<%
EventLog aLog = new EventLog();
aLog.Log = "System";
aLog.MachineName = "."; // Lokale Maschine
string strImage = ""; // Icon fur das Event

Response.Write("<p>There are " + aLog.Entries.Count +
" entries in the System event log.</p>");

foreach (EventLogEntry entry in aLog.Entries)
{
switch (entry.EntryType)
{
case EventLogEntryType.Warning:
strImage = "warning.png";
break;
case EventLogEntryType.Error:
strImage = "error.png";
break;
default:
strImage = "info.png";
break;
}
Response.Write("<img src=\"" + strImage + "\"> | ");
Response.Write(entry.TimeGenerated.ToString() + " | ");
Response.Write(entry.Source + " | ");
Response.Write(entry.EventID.ToString() + "
\r\n");
}
%>


The classes for the Event Log are found in the Namespace System.Diagnostics which is bound in at the
beginning of the page. Opening the log is in itself straightforward: create a new EventLog object, specify
the Log and the MachineName ("." is the local machine). And we're ready to read from the Event Log.

This is done in a foreach loop. To make the listing less unimaginative, I put the correct icon before each
entry. By the way, the listing of entries is the reverse of the usual order in the Event Viewer: here, the
oldest entries are listed first.

More elegant with the DataGrid
ASP.NET comes with many innovations, especially for displaying data. And the good part about that is that
the data does not always have to come out of a database. This also is true for the DataGrid Web Control
which, as the name says, creates a table (grid) out of the data. The only requirement is that the data
source supports the ICollection interface - and the Entries Collection of the EventLog does just that.

The following source code (datagrid.aspx) shows how simple using the DataGrid is:

<% @Page Language="C#" %>
<% @Import Namespace="System.Diagnostics" %>
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
EventLog aLog = new EventLog();
aLog.Log = "System";
aLog.MachineName = ".";

LogGrid.DataSource = aLog.Entries;
LogGrid.DataBind();
}
</script>
<body bgcolor="#ffffff">

<h3>System Event Log</h3>

<form runat="server">
<ASP:DataGrid id="LogGrid" runat="server"
BorderColor="black"
BorderWidth="1"
GridLines="Both"
CellPadding="3"
CellSpacing="0"
Font-Name="Verdana"
Font-Size="8pt"
HeaderStyle-BackColor="#aaaadd"
/>
</form>

</body>
</html>


The DataGrid Control only contains formatting instructions, nothing else. The Grid is filled via the
Page_Load event, which merely opens the Event Log and then assigns the Entries as the DataSource property
of the DataGrid. With the call of DataBind the data is poured into the table - all of it.

The amount of data is not exactly small, as the EventLogEntry class possesses many properties and we just
want to have a neat overview. The next section deals with implementing this restriction.

Restricting fields in the DataGrid
Our goal is to display only certain fields. This time, before getting into the code, we take a quick look
at the output:


In principle, this output is very similar to the preceding example, the only difference being the number
of columns displayed. This restriction is being done in the DataGrid tag itself (speccolsonly.aspx
contains the entire code):


<asp:DataGrid id="LogGrid" runat="server"
BorderColor="black"
BorderWidth="1"
GridLines="Both"
CellPadding="3"
CellSpacing="0"
Font-Name="Verdana"
Font-Size="8pt"
HeaderStyle-BackColor="#aaaadd"
AutoGenerateColumns="false">
<property name="Columns">
<asp:BoundColumn HeaderText="TOF" DataField="EntryType" />
<asp:BoundColumn HeaderText="Date/Time" DataField="TimeGenerated"/>
<asp:BoundColumn HeaderText="Source" DataField="Source"/>
<asp:BoundColumn HeaderText="Event ID" DataField="EventID"/>
</property>
</asp:DataGrid>


The first important step is to set the AutoGenerateColumns attribute to false. This prevents the
automatical display of all properties. Now we can specify which columns we want.

I am using here four bound columns (bound to the data source).The HeaderText is being displayed in the top
row and in DataField the property to be read for filling this column is given.

I kept this example with columns intentionally simple. There are many more column types and when you start
playing around with the formatting, there are no limits to the designer's 'frenzy'. More than enough
examples for this can be found in the QuickStart tutorial.


Paging in the DataGrid
For finishing off, I want to use another feature of the DataGrid which is an old acquaintance for DB
programmers - paging. The advantage of the DataGrid is that paging needs (almost) no code. This might look
like the following:


This time I have again taken the whole source code of paging.aspx into the article for reading through:


<% @Page Language="C#" %>
<% @Assembly Name="System.Diagnostics" %>
<% @Import Namespace="System.Diagnostics" %>
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
BindGrid();
}
void LogGrid_Page(Object sender, DataGridPageChangedEventArgs e)
{
BindGrid();
}
void BindGrid()
{
EventLog aLog = new EventLog();
aLog.Log = "System";
aLog.MachineName = ".";

LogGrid.DataSource = aLog.Entries;
LogGrid.DataBind();
}
</script>
<body bgcolor="#ffffff">
<h3>System Event Log</h3>
<form runat="server">
<asp:DataGrid id="LogGrid" runat="server"
AllowPaging="True"
PageSize="10"
PagerStyle-Mode="NumericPages"
PagerStyle-HorizontalAlign="Right"
PagerStyle-NextPageText="Next"
PagerStyle-PrevPageText="Prev"
OnPageIndexChanged="LogGrid_Page"
BorderColor="black"
BorderWidth="1"
GridLines="Both"
CellPadding="3"
CellSpacing="0"
Font-Name="Verdana"
Font-Size="8pt"
HeaderStyle-BackColor="#aaaadd"
AutoGenerateColumns="false">
<property name="Columns">
<asp:BoundColumn HeaderText="TOF" DataField="EntryType" />
<asp:BoundColumn HeaderText="Date/Time" DataField="TimeGenerated"/>
<asp:BoundColumn HeaderText="Source" DataField="Source"/>
<asp:BoundColumn HeaderText="Event ID" DataField="EventID"/>
</property>
</asp:DataGrid>
</form>
</body>
</html>


The first changes are found in the DataGrid control:

AllowPaging="True"
PageSize="10"
PagerStyle-Mode="NumericPages"
PagerStyle-HorizontalAlign="Right"
PagerStyle-NextPageText="Next"
PagerStyle-PrevPageText="Prev"
OnPageIndexChanged="LogGrid_Page"


The two most important attributes are the first and the last one: AllowPaging and OnPageIndexChanged. The
first enables paging, the second is the event method triggered upon change of the page. The remaining
attributes are of cosmetic nature.

As we are working with a collection instead of database supplied data in this example, I made it (almost
too) easy for myself: I'm just binding the data onto the grid again. For better performance - especially
with databases - the data also should be reloaded in 'snippets'.

Conclusion
The actual purpose of today's article was not so much to learn reading the Event Log, but rather to
demonstrate how versatile the uses of the DataGrid are outside the main application field of database
programming. Very much of the functionality can be used, however, editing of Event Log entries (read-only)
doesn't make sense and thus cannot be used.
webasp.net