pdf417 c# Figure 2-11. Separating n-level undo into Core.UndoableBase in C#.NET

Make PDF417 in C#.NET Figure 2-11. Separating n-level undo into Core.UndoableBase

Figure 2-11. Separating n-level undo into Core.UndoableBase
PDF-417 2d Barcode Drawer In Visual C#
Using Barcode printer for .NET Control to generate, create PDF 417 image in .NET applications.
www.OnBarcode.com
Recognize PDF-417 2d Barcode In C#
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
CHAPTER 2 FRAMEWORK DE SIGN
PDF 417 Creator In Visual C#.NET
Using Barcode drawer for VS .NET Control to generate, create PDF417 image in .NET applications.
www.OnBarcode.com
2D Creation In Visual C#
Using Barcode generator for .NET framework Control to generate, create 2D Barcode image in .NET applications.
www.OnBarcode.com
At first glance, it might appear that you could use .NET serialization to implement undo functionality: what easier way to take a snapshot of an object s state than to serialize it into a byte stream Unfortunately, this isn t as easy as it might sound, at least when it comes to restoring the object s state. Taking a snapshot of a Serializable object is easy and can be done with code similar to this: [Serializable] public class Customer { public byte[] Snapshot() { using (var buffer = new MemoryStream()) { var formatter = new BinaryFormatter(); formatter.Serialize(buffer, this); buffer.Position = 0; return buffer.ToArray(); } } } This converts the object into a byte stream, returning that byte stream as an array of type byte. That part is easy it s the restoration that s tricky. Suppose that the user now wants to undo the changes, requiring that the byte stream be restored back into the object. The code that deserializes a byte stream looks like this: [Serializable] public class Customer { public Customer Deserialize(byte[] state) { using (var buffer = new MemoryStream(state)) { var formatter = new BinaryFormatter(); return (Customer) formatter.Deserialize(buffer); } } } Notice that this function returns a new customer object. It doesn t restore the existing object s state; it creates a new object. Somehow, you would have to tell any and all code that has a reference to the existing object to use this new object. In some cases, that might be easy to do, but it isn t always trivial. In complex applications, it s hard to guarantee that other code elsewhere in the application doesn t have a reference to the original object; and if you don t somehow get that code to update its reference to this new object, it will continue to use the old one. What s needed is some way to restore the object s state in place, so that all references to the current object remain valid but the object s state is restored. This is the purpose of the UndoableBase class.
Make Barcode In C#.NET
Using Barcode creator for .NET Control to generate, create Barcode image in .NET framework applications.
www.OnBarcode.com
Printing Linear Barcode In C#.NET
Using Barcode creator for .NET framework Control to generate, create Linear 1D Barcode image in VS .NET applications.
www.OnBarcode.com
UndoableBase
Data Matrix Generation In C#
Using Barcode generator for .NET Control to generate, create Data Matrix ECC200 image in Visual Studio .NET applications.
www.OnBarcode.com
GS1 - 12 Drawer In C#.NET
Using Barcode drawer for .NET Control to generate, create UPC - E1 image in VS .NET applications.
www.OnBarcode.com
The BusinessBase class inherits from UndoableBase and thereby gains n-level undo capabilities. Because all business objects inherit from BusinessBase, they too gain n-level undo. Ultimately, the n-level undo capabilities are exposed to the business object and to UI developers via three methods:
Drawing PDF 417 In VS .NET
Using Barcode generation for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
www.OnBarcode.com
Recognizing PDF-417 2d Barcode In Visual Studio .NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
C HAPTE R 2 FRA MEWORK DES IGN
Drawing QR Code 2d Barcode In .NET
Using Barcode encoder for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
www.OnBarcode.com
Making Barcode In Visual Basic .NET
Using Barcode printer for .NET Control to generate, create Barcode image in .NET applications.
www.OnBarcode.com
BeginEdit() tells the object to take a snapshot of its current state, in preparation for being edited. Each time BeginEdit() is called, a new snapshot is taken, allowing the state of the object to be trapped at various points during its life. The snapshot will be kept in memory so the data can be easily restored to the object if CancelEdit() is called. CancelEdit() tells the object to restore the object to the most recent snapshot. This effectively performs an undo operation, reversing one level of changes. If CancelEdit() is called the same number of times as BeginEdit(), the object will be restored to its original state. ApplyEdit() tells the object to discard the most recent snapshot, leaving the object s current state untouched. It accepts the most recent changes to the object. If ApplyEdit() is called the same number of times as BeginEdit(), all the snapshots will be discarded, essentially making any changes to the object s state permanent. Sequences of BeginEdit(), CancelEdit(), and ApplyEdit() calls can be combined to respond to the user s actions within a complex Windows Forms UI. Alternatively, you can totally ignore these methods, taking no snapshots of the object s state. In such a case, the object will incur no overhead from n-level undo, but it also won t have the ability to undo changes. This is common in web applications in which the user has no option to cancel changes. Instead, the user simply navigates away to perform some other action or view some other data. The Csla.Core.ISupportUndo interface exists to allow UI developers and framework authors to polymorphically invoke these three methods on any object that supports the concept. The BusinessBase and BusinessListBase classes already implement this interface.
Scanning QR Code ISO/IEC18004 In Visual C#
Using Barcode reader for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
Barcode Creator In Java
Using Barcode generator for Android Control to generate, create Barcode image in Android applications.
www.OnBarcode.com
Encode DataMatrix In None
Using Barcode creator for Online Control to generate, create Data Matrix ECC200 image in Online applications.
www.OnBarcode.com
QR Code 2d Barcode Generation In Java
Using Barcode drawer for Android Control to generate, create QR Code image in Android applications.
www.OnBarcode.com
EAN-13 Decoder In Visual C#
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
EAN 128 Creation In None
Using Barcode encoder for Office Word Control to generate, create GTIN - 128 image in Word applications.
www.OnBarcode.com
ECC200 Drawer In Java
Using Barcode encoder for Java Control to generate, create Data Matrix 2d barcode image in Java applications.
www.OnBarcode.com
Printing Code 128 In Objective-C
Using Barcode printer for iPad Control to generate, create Code-128 image in iPad applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.