Simple .NET/ASP.NET PDF document editor web control SDK

You ll now look at a way to draw the tree using controls. The WinForms library defines a TreeView class, which is specifically for displaying tree-like structures, so you ll use this control to display the tree. To use TreeView, you create an instance of it and configure it by setting its properties and calling its methods. Most important, you add to its Nodes collection the nodes you want to display. Once the control is ready to be displayed, you add it to the form s Controls collection. The TreeView class uses TreeNode objects to represent nodes, so you ll define the function mapTreeToTreeNode to recursively walk the tree structure and create a TreeNode graph. The program in Listing 8-2 produces the tree in Figure 8-3. Listing 8-2. Drawing a Tree via a TreeView Control #light open System.Windows.Forms // The tree type type 'a Tree = | Node of 'a Tree * 'a Tree | Leaf of 'a // The definition of the tee let tree = Node( Node( Leaf "one", Node(Leaf "two", Leaf "three")), Node( Node(Leaf "four", Leaf "five"), Leaf "six")) // A function to transform our tree into a tree of controls let mapTreeToTreeNode t = let rec mapTreeToTreeNodeInner t (node : TreeNode) = match t with | Node (l, r) -> let newNode = new TreeNode("Node") node.Nodes.Add(newNode) |> ignore mapTreeToTreeNodeInner l newNode mapTreeToTreeNodeInner r newNode | Leaf x -> node.Nodes.Add(new TreeNode(any_to_string x)) |> ignore let root = new TreeNode("Root") mapTreeToTreeNodeInner t root root

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Figure 5-40. NXT Quick Start robot with Light Sensors The NXT-G program in Figure 5-41 is an endless loop that reads the two Light Sensors and adjusts the power to the two motors. Because the homebrew Light Sensor s Raw value decreases with increasing light level, the first Math block subtracts the Raw value from 1,000. This makes a value that s larger with brighter light. The second Math block divides the number by 10 to scale it into the 0-to-100 range used for the power input to the Motor block. All you need to change between the 2a and 2b vehicles programs is the motor designator letters B and C.

// create the form object let form = let temp = new Form() let treeView = new TreeView(Dock = DockStyle.Fill) treeView.Nodes.Add(mapTreeToTreeNode tree) |> ignore treeView.ExpandAll() temp.Controls.Add(treeView) temp Application.Run(form)

The techniques for using the POST method instead of GET are identical except for how the request parameters are sent to the server Recall that when using GET, the name/value pairs are appended to the destination URL The POST method sends the same query string as part of the request body Clicking the Send Parameters Using POST button calls the doRequestUsingPOST function Like the doRequestUsingGET function, it starts by creating an instance of the XMLHttpRequest object The script continues by creating the query string that contains the parameters to be sent to the server Note that the query string is not concatenated with the destination URL The XMLHttpRequest object s open() method is invoked, this time specifying POST as the request method in addition to specifying the bare destination URL.

Figure 5-41. Vehicle 2b NXT-G program Suppose that model 2a is in a dark room, and a bright light that s in front and to the right of the vehicle is turned on, as in Figure 5-42. The right photo sensor receives more light than the left, and therefore the right motor turns faster than the left. This causes the vehicle to go forward but turn to the left, avoiding the light source. The vehicle behaves as if it hates light.

Figure 8-3 A TreeView control used to view a tree This code is about half the length of Listing 8-1, when you drew the tree yourself It is also more functional, because it allows you to fold away parts of the tree in which you re not interested This greatly improves the size of tree that can be manageably displayed In this example, you use the dock style to control how the control looks You do this by setting the control s Dock property with a member of the DockStyle enumeration Docking means that the control will take up as much space as available in the form that contains it on the left side if you use DockStyleLeft, on the right side if you use DockStyleRight, at the top if you use DockStyleTop, on the bottom if you use DockStyle.

The onreadystatechange property is set to the handleStateChange function, allowing the response to be processed in the same way as the GET method To ensure that the server knows that the request parameters can be found within the request body, the setRequestHeader is called, setting the Content-Type.