rdlc data matrix

rdlc data matrix

rdlc data matrix

Instead of using this property, you ll bind the control when the page first loads This gives you the chance to insert the items immediately, before any other data binding actions take place: Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) If (Not PageIsPostBack) Then ' Trigger the sourceEmployeeCities query, and bind the results lstCitiesDataSource = sourceEmployeeCitiesSelect(DataSourceSelectArgumentsEmpty) lstCitiesDataBind() ' Add the two new items, and select the first lstCitiesItemsInsert(0, "(Choose a City)") lstCitiesItemsInsert(1, "(All Cities)") lstCitiesSelectedIndex = 0 End If End Sub In this example, the data binding for the list control is performed only once, when the page is requested for the first time After that, the values in view state are used instead This code is identical for the SqlDataSource and the ObjectDataSource That s not true for the remainder of the example..

Depending on the scenario, you might be able to respond to data source control events, but they aren t always fired at the point you need to perform your logic Essentially, data binding tasks take place in this order: 1 The page object is created (based on the aspx file) 2 The page life cycle begins, and the PageInit and PageLoad events fire 3 All other control events fire 4 The data source controls perform any updates If a row is being updated, the Updating and Updated events fire If a row is being inserted, the Inserting and Inserted events fire If a row is being deleted, the Deleting and Deleted events fire 5 The PagePreRender event fires 6 The data source controls perform any queries and insert the retrieved data in the linked controls The Selecting and Selected events fire at this point 7.

The GridView examples you ve seen so far have set the GridView.AutoGenerateColumns property to true. When this property is set, the GridView uses reflection to examine that data object and finds all the fields (of a record) or properties (of a custom object). It then creates a column for each one, in the order that it finds it. This automatic column generation is good for creating quick test pages, but it doesn t give you the flexibility you ll usually want. For example, what if you want to hide columns, change their order, or configure some aspect of their display, such as the formatting or heading text In all of these cases, you ll need to set AutoGenerateColumns to false and define the columns yourself in the <Columns> section of the GridView control tag.

The next challenge is to intercept clicks on either of the first two items. You can accomplish this by handling the data source Selecting event, which occurs just before the query is executed. You can then check the parameters that are about to be supplied and cancel the operation if needed.

The page is rendered and disposed It's important to realize that this process is repeated for each request That means the data source controls query the database every time the page is posted back If this sounds like unnecessary work for your database well, it is The best solution is to use caching so that the data you retrieve is kept in memory and reused, bypassing the database on subsequent requests You'll master this technique in 11..

It s possible to have AutoGenerateColumns set to true and define columns in the <Columns> section. In this case, the columns you explicitly defined are added before the autogenerated columns. This technique was used in the previous chapter to create a GridView with automatically generated bound columns and a manually defined column with edit controls. However, for the most flexibility you ll usually want to explicitly define every column.

Here s the complete code: Protected Sub sourceEmployees_Selecting(ByVal sender As Object, ByVal e As SqlDataSourceSelectingEventArgs) If CStr(e.Command.Parameters("@City").Value) = "(Choose a City)" Then ' Do nothing. e.Cancel = True Else If CStr(e.Command.Parameters("@City").Value) = "(All Cities)" Then ' Manually change the command. e.Command.CommandText = "SELECT * FROM Employees" End If End Sub This brute-force approach changing the command using a hard-coded query is ugly. Another approach is to cancel the operation, call another method that returns the appropriate data, and bind that. However, that forces you to do a fair bit of work manually, and mixing manual and automatic data binding can quickly get confusing. Unfortunately, no perfect solution exists.