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Creating a Real-World Application |
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expect them to. This is all good stuff, but your file-copy application still doesn t copy any files yet. That s because you haven t created the event handlers for the buttons.
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Handling the Button Events
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The four buttons on the page (Clear, Copy, Delete, and Cancel) are the controls that will do the actual work of the application. In fact, only the Copy button is particularly challenging, but we ll take each one in turn.
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Handling the Clear button event
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The purpose of the Clear button is to clear any checked boxes in the source TreeView. Given the SetCheck( ) method that you developed earlier, handling the Clear button s Click event is trivial. In the Design tab, double-click on the Clear button to create its default event handler (Click). Then add this bit of code to the handler:
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private void btnClear_Click( object sender, System.EventArgs e ) { foreach ( TreeNode node in tvwSource.Nodes ) { SetCheck( node, false ); } }
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All you re doing here is calling the SetCheck( ) method on the root nodes and telling them to recursively uncheck all their contained nodes.
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Implementing the Copy button event
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Now that you can check the files and pick the target directory, you re ready to handle the Copy click event. The very first thing you need to do is to get a list of which files were selected. What you want is an array of FileInfo objects, but you have no idea how many objects will be in the list. This is a perfect job for a generic List. Double-click the Copy button to create the event handler. Then add the following code to call a method called GetFileList( ), which will take responsibility for filling the list:
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private void btnCopy_Click( object sender, System.EventArgs e ) { List<FileInfo> fileList = GetFileList( );
Let s pick that method apart before returning to the event handler. Create the new method below the btnCopy_Click handler. Start by instantiating a new List object to hold the strings representing the names of all the files selected:
private List<FileInfo> GetFileList( ) { List<string> fileNames = new List<string>( );
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18: Creating Windows Applications
To get the selected filenames, you can iterate through the source TreeView control:
foreach ( TreeNode theNode in tvwSource.Nodes ) { GetCheckedFiles( theNode, fileNames ); }
To see how this works, you ll create the GetCheckedFiles( ) method before you go any further with GetFileList( ). Create this method now below GetFileList( ). This method is pretty simple: it examines the node it was handed. If that node has no children (node.Nodes.Count == 0), it is a leaf. If that leaf is checked, you get the full path and add it to the ArrayList passed in as a parameter. Add the following code to your new method:
private void GetCheckedFiles( TreeNode node,List<string> fileNames ) { // if this is a leaf... if ( node.Nodes.Count == 0 ) { // if the node was checked... if ( node.Checked ) { // add the full path to the arrayList
fileNames.Add(node.FullPath);
} }
If the node is not a leaf, you recurse down the tree, finding the child nodes. Add the following code to complete the method:
else { foreach (TreeNode n in node.Nodes) { GetCheckedFiles(n,fileNames); } } }
This returns the List filled with all the filenames. Back in GetFileList( ), you ll use this List of filenames to create a second List, this time to hold the actual FileInfo objects this will give you the actual files to copy, not just their names. You start by creating the new List<FileInfo>. Add this code to GetFileList( ):
List<FileInfo> fileList = new List<FileInfo>( );
You re using type-safe List objects here so that the compiler will flag any objects added to the collection that aren t of type FileInfo. You can now iterate through the filenames in fileNames, picking out each name and instantiating a FileInfo object with it. You can detect whether a given name is a file or a directory by calling the Exists property, which will return false if the File object you created is actually a directory. If it is a File, you can add it to the fileList that you just created. Add the following code to GetFileList( ):
foreach ( string fileName in fileNames ) { FileInfo file = new FileInfo( fileName ); if ( file.Exists ) { fileList.Add( file ); } }
It would be a good idea to work your way through the list of selected files in order from largest to smallest so that you can pack the target disk as tightly as possible. You must therefore sort the List. You can call the Sort( ) method of the List, but how will it know how to sort FileInfo objects To solve this, you must pass in an IComparer<T> interface. You learned about using interfaces back in 13, and generics in 14. You ll create a class called FileComparer that will implement this generic interface for FileInfo objects. Add the following code as a nested class inside the FrmFileCopier class, but outside any existing methods:
public class FileComparer : IComparer<FileInfo> {
This class has only one method, Compare( ), which takes two FileInfo objects as arguments. Add the following method to the class:
public int Compare(FileInfo file1, FileInfo file2) {
The normal approach is to return 1 if the first object (file1) is larger than the second (file2), to return 1 if the opposite is true, and to return 0 if they are equal. In this case, however, you want the list sorted from big to small, so you should reverse the return values.
Because this is the only use of the Compare method, it is reasonable to put this special knowledge (that the sort is from big to small) right into the Compare method itself. The alternative is to sort small to big, and have the calling method reverse the results.
The Length property of the FileInfo class makes it easy to compare the size of the two files. Add the following code to the Compare( ) method:
public int Compare(FileInfo file1, FileInfo file2) { if ( file1.Length > file2.Length ) { return -1; } if ( file1.Length < file2.Length ) { return 1; }
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