generate qr code programmatically c# Part II in C#.NET

Generation QR Code 2d barcode in C#.NET Part II

Part II
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Recognizing QR Code ISO/IEC18004 In Visual C#
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ASP.NET Pages and Server Controls
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the data source control needs to get an instance of the business class. You can write the handler to retrieve an existing instance of the class and return that to the data source control:
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// Handle the ObjectCreating event on the data source control public void BusinessObjectBeingCreated(object sender, ObjectDataSourceEventArgs e) { BusinessObject bo = RetrieveBusinessObjectFromPool(); if (bo == null) bo = new BusinessObject(); e.ObjectInstance = bo; }
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Likewise, in ObjectDisposing you store the instance again and cancel the disposing operation being executed:
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// Handle the ObjectDisposing event on the data source control public void BusinessObjectBeingDisposed(object sender, ObjectDataSourceDisposingEventArgs e) { ReturnBusinessObjectToPool(e.ObjectInstance); e.Cancel = true; }
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The ObjectDisposing event allows you to perform cleanup actions in your business object before the ObjectDataSource calls the business object s Dispose method. If you re caching the business object, as the preceding code has done, be sure to set the cancel flag so that the business object s Dispose method isn t invoked and the cached object isn t as a result stored in a disposed state.
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Setting Up for Paging
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Three properties participate in paging: EnablePaging, StartRowIndexParameterName, and MaximumRowsParameterName. As the name clearly suggests, EnablePaging toggles support for paging on and off. The default value is false, meaning that paging is not turned on automatically. ObjectDataSource provides an infrastructure for paging, but actual paging must be implemented in the class bound to ObjectDataSource. In the following code snippet, the Customers class has a method, LoadByCountry, that takes two additional parameters to indicate the page size and the index of the first record in the page. The names of these two parameters must be assigned to MaximumRowsParameterName and StartRowIndexParameterName, respectively.
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<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" TypeName="DAL.CustomerRepository" StartRowIndexParameterName="firstRow" MaximumRowsParameterName="totalRows" SelectMethod="LoadByCountry"> <SelectParameters> <asp:ControlParameter Name="country" ControlID="Countries"
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10 Data Binding
PropertyName="SelectedValue" /> <asp:ControlParameter Name="totalRows" ControlID="PageSize" PropertyName="Text" /> <asp:ControlParameter Name="firstRow" ControlID="FirstRow" PropertyName="Text" /> </SelectParameters> </asp:ObjectDataSource>
The implementation of paging is up to the method and must be coded manually. LoadByCountry provides two overloads, one of which supports paging. Internally, paging is actually delegated to FillCustomerList.
public static CustomerCollection LoadByCountry(string country) { return LoadByCountry(country, -1, 0); } public static CustomerCollection LoadByCountry(string country, int totalRows, int firstRow) { CustomerCollection coll = new CustomerCollection(); using (SqlConnection conn = new SqlConnection(ConnectionString)) { SqlCommand cmd; cmd = new SqlCommand(CustomerCommands.cmdLoadByCountry, conn); cmd.Parameters.AddWithValue("@country", country); conn.Open(); SqlDataReader reader = cmd.ExecuteReader(); HelperMethods.FillCustomerList(coll, reader, totalRows, firstRow); reader.Close(); conn.Close(); } return coll; }
As you can see in the companion source code, FillCustomerList simply scrolls the whole result set using a reader and discards all the records that don t belong in the requested range. You could perhaps improve upon this approach to make paging smarter. What s important here is that paging is built into your business object and exposed by data source controls to the pageable controls through a well-known interface.
Updating and Deleting Data
To update underlying data using ObjectDataSource, you need to define an update/insert/ delete method. All the actual methods you use must have semantics that are well suited to implement such operations. Here are some good prototypes for the update operations:
public public public public static static static static void void void void Save(Employee emp) Insert(Employee emp) Delete(Employee emp) Delete(int id)
Part II
ASP.NET Pages and Server Controls
More so than with select operations, update operations require parameters. To update a record, you need to pass new values and one or more old values to make sure the right record to update is located and to take into account the possibility of data conflicts. To delete a record, you need to identify it by matching a supplied primary key parameter. To specify input parameters, you can use command collections such as UpdateParameters, InsertParameters, or DeleteParameters. Let s examine update/insert scenarios first. To update an existing record or insert a new one, you need to pass new values. This can be done in either of two ways listing parameters explicitly or aggregating all parameters in an all-encompassing data structure. The prototypes shown previously for Save and Insert follow the latter approach. An alternative might be the following:
void Save(int id, string firstName, string lastName, ...) void Insert(string firstName, string lastName, ...)
You can use command parameter collections only if the types involved are simple types numbers, strings, dates. To make a custom class such as Employee acceptable to the ObjectDataSource control, you need to set the DataObjectTypeName property:
<asp:ObjectDataSource ID="RowDataSource" runat="server" TypeName="DAL.EmployeeRepository" SelectMethod="Load" UpdateMethod="Save" DataObjectTypeName="DAL.Employee"> <SelectParameters> <asp:ControlParameter Name="id" ControlID="GridView1" PropertyName="SelectedValue" /> </SelectParameters> </asp:ObjectDataSource>
The preceding ObjectDataSource control saves rows through the Save method, which takes an Employee object. Note that when you set the DataObjectTypeName property, the UpdateParameters collection is ignored. The ObjectDataSource instantiates a default instance of the object before the operation is performed and then attempts to fill its public members with the values of any matching input fields found around the bound control. Because this work is performed using reflection, the names of the input fields in the bound control must match the names of public properties exposed by the object in the DataObjectTypeName property. A practical limitation you must be aware of is the following: you can t define the Employee class using complex data types, as follows:
public class Employee { public string LastName { get; set; } public string FirstName { get; set; } ... public Address HomeAddress {...} }
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