how to create barcode in vb.net 2012 DISKDIFF: MORE SOPHISTICATION in Visual C#.NET

Making PDF-417 2d barcode in Visual C#.NET DISKDIFF: MORE SOPHISTICATION

CHAPTER 36 DISKDIFF: MORE SOPHISTICATION
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A Cancel Button
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To keep things simple, this example will use a button to cancel the processing. Using the designer, you can add a Cancel button at the lower-left corner of the form on top of the tree view. So that it isn t in the way, set the visibility to false. When processing is started, the visibility is set to true, and the button is now visible and selectable. The event handler that s associated with completing the population will set the visibility back to false when the processing is completed or aborted. Figure 36-1 shows a view of the application while processing a big directory tree.
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Figure 36-1. DiskDiff with a Cancel button You now have an application that can be interrupted. In this case, using threads was a simple way to get what you wanted. Another way to do this is to use the asynchronous call mechanism in the .NET CLR (see 31).
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Decorating the TreeView
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The application displays the sizes well, but it s fairly difficult to tell where the disk space is used based upon the numbers. What you need is a graphical representation of the amount of space used by each directory and file. The TreeView control can put bitmaps in front of each item. To do this, an ImageList that contains all the bitmaps is attached to the TreeView, and then the index of the desired bitmap is set for each item in the tree. To get started, you need to add an ImageList to the form and then populate it with images. First, drag an ImageList object from the Toolbox to the form. You can then add images through the Collections property in the property window. (We drew the images for this project using Paint Shop Pro.)
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CHAPTER 36 DISKDIFF: MORE SOPHISTICATION
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To hook up the ImageList to the TreeView, set the ImageList property in the TreeView control to the name of the ImageList in the form. The next task is to figure out which image to present for each item in the list. The bitmaps are pie charts representing the percentage of the total space an item used. You can therefore determine the index by multiplying the fraction of space used by the number of images (8) to get the index. That requires you to modify the population function as follows: public void PopulateTree(TreeNodeCollection treeNodeCollection, DirectoryNode directoryNode, float fractionUsed) { TreeNode treeNode = new TreeNode(directoryNode.NameSize); treeNode.ImageIndex = FractionToIndex(fractionUsed); treeNodeCollection.Add(treeNode); // As we walk though the tree, we need to figure out the // percentages for each item. We do that based upon the // full size of this directory. float dirSize = directoryNode.SizeTree; foreach (DirectoryNode subdir in directoryNode.GetDirectories()) { PopulateTree(treeNode.Nodes, subdir, subdir.SizeTree / dirSize); } foreach (FileNode fileNode in directoryNode.GetFiles()) { TreeNode treeFileNode = new TreeNode(fileNode.NameSize); treeFileNode.ImageIndex = FractionToIndex(fileNode.Size / dirSize); treeNode.Nodes.Add(treeFileNode); } } The percentage is passed into the PopulateTree() function because each directory creates its own node. The top node is passed in the value 1.0, since it obviously contains all the size in the tree. The fraction of each element is computed based on the size of that element and the size of the directory it s in, and the index for that fraction is obtained from the FractionToIndex() function. Figure 36-2 shows how a tree looks with all the nodes expanded. The program is starting to get useful, but it still has a few problems. One is that populating the TreeView object with all the nodes of the directory tree can take a long time and use lots of memory if the directory tree is large.
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CHAPTER 36 DISKDIFF: MORE SOPHISTICATION
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Figure 36-2. TreeView with size icons
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Expand-o-Matic
Instead of populating the whole tree, you ll populate only the currently visible portion of the tree initially. When a user clicks the plus sign to expand a directory, you ll populate the newly visible section. Hooking up to the BeforeExpand event is fairly easy. When this event occurs, a TreeViewCancelEventArgs is passed, and that class contains the node that s expanding. The event code will merely need to figure out what DirectoryNode object corresponds to the node passed with the event. When dealing with a tree view control in the MFC framework or directly in Win32, you can store a value with each tree node and use this value to point to the object that corresponds to the tree node. However, WinForms doesn t provide access to this, so you ll need to use another approach. One approach is to change DirectoryNode and FileNode so they re derived from TreeNode and then store those directly. This works fine but will complicate those classes, since they now depend on the WinForms classes. Another approach is to define a class derived from TreeNode that has a reference to the DirectoryNode or FileNode object for that node. That class is simple and looks like this: public class MyTreeNode: TreeNode { object node; // DirectoryNode or TreeNode public MyTreeNode(string text, object node): base(text) { this.node = node; }
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