Figure 81 Custom Type Shown in a ListBox Control in .NET

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Figure 81 Custom Type Shown in a ListBox Control
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Because the ListView control can show items with multiple columns and states, its Items collection is populated with instances of the ListViewItem class Each item has a Text property, which represents the text of the first column, and then a collection of subitems that represent the rest of the columns: void Form1_Load(object sender, EventArgs e) { Person[] boys = { new Person("Tom", 7), new Person("John", 8) }; foreach( Person boy in boys ) { // NOTE: Assumes Columns collection already has 2 columns ListViewItem item = new ListViewItem(); itemText = boyName; itemSubItemsAdd(boyAgeToString()); listView1ItemsAdd(item); } } Figure 82 shows the multicolumn ListView filled via this code
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Figure 82 Multicolumn ListView
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The TreeView control shows a hierarchy of items that are instances of the TreeNode type Each TreeNode object contains the text, some optional images, and a Nodes collection containing subnodes Which node you add to determines where the newly added node will show up in the hierarchy: void Form1_Load(object sender, EventArgs e) { TreeNode parentNode = new TreeNode(); parentNodeText = "Chris"; // Add a node to the root of the tree treeView1NodesAdd(parentNode); TreeNode childNode = new TreeNode(); childNodeText = "John"; // Add a node under an existing node parentNodeNodesAdd(childNode); } Figure 83 shows the result of filling a TreeView control using this sample code
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Figure 83 A Parent Node and a Child Node in a TreeView Control
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The DataGrid control gets its data from a collection set by using the DataSource property: void Form1_Load(object sender, EventArgs e) { Person[] boys = { new Person("Tom", 7), new Person("John", 8) }; dataGrid1DataSource = boys; } The DataGrid shows each public property of the objects in the collection as a column, as shown in Figure 84
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Figure 84 A DataGrid Showing a Collection of Custom Types
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A DataGrid can also show hierarchical data and do all kinds of other fancy things You'll find many more details about the DataGrid control in 13: Data Binding and Data Grids
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List Item Selection
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Each of the list controls exposes a property to report the current selection (or a list of selections, if the list control supports multiple selections) and fires an event when the selection changes For example, the following code handles the SelectedIndexChanged event of the ListBox control and uses the SelectedIndex property to pull out the currently selected object: void listBox1_SelectedIndexChanged(object sender, EventArgs e) { // Get the selected object object selection = listBox1Items[listBox1SelectedIndex]; MessageBoxShow(selectionToString()); // The object is still the same type as when we added it Person boy = (Person)selection; MessageBoxShow(boyToString()); } Notice that the SelectedIndex property is an offset into the Items collection that pulls out the currently selected item The item comes back as the "object" type, but a simple cast allows us to treat it as an instance of exactly the same type as when it was added This is useful when a custom type shows data using ToString but has another characteristic, such as a unique identifier, that is needed programmatically In fact, for the list controls that don't take objects, such as TreeView and ListView, each of the items supports a Tag property for stashing away unique ID information: void Form1_Load(object sender, EventArgs e) { TreeNode parentNode = new TreeNode(); parentNodeText = "Chris"; parentNodeTag = "000-00-0000"; // Put in extra info treeView1NodesAdd(parentNode); } void treeView1_AfterSelect(object sender, TreeViewEventArgs e) { TreeNode selection = treeView1SelectedNode; object tag = selectionTag; // Pull out extra info MessageBoxShow(tagToString()); } List controls support either custom types or the Tag property but not both The idea is that because the lists contain instances of custom types, any extra information can simply be kept as needed Unfortunately, the lack of a Tag property makes it more difficult to associate ID information with simple types, such as strings However, a simple wrapper will allow you to add a tag to a list item of any type: class TaggedItem { public object Item; public object Tag; public TaggedItem(object item, object tag) { thisItem = item; thisTag = tag; } public override string ToString() { return ItemToString(); } }
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void Form1_Load(object sender, EventArgs e) { // Add two tagged strings comboBox1ItemsAdd(new TaggedItem("Tom", "000-00-0000)); comboBox1ItemsAdd(new TaggedItem("John", "000-00-0000")); } void comboBox1_SelectedIndexChanged(object sender, EventArgs e) { TaggedItem selection = (TaggedItem)comboBox1Items[comboBox1SelectedIndex]; object tag = selectionTag; MessageBoxShow(tagToString()); } The TaggedItem wrapper keeps track of an item and a tag The ToString method lets the item decide how it should be displayed, and the Item and Tag properties expose the parts of the TaggedItem object for use in processing the current selection
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