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The mouse-down event identifies where the click occurred in the X-axis. The challenge is to determine if the user wants to expand or collapse the node or just wants to select it.
#Microsoft access product code code#
The code for this event is the main switchboard for changing the tree’s appearance. Expanding and Collapsing Nodes - Signaling ContextĪs the user clicks in the text area of each row, a mouse-down event is raised. You will find an interesting list of these symbols here. Unicode symbols are declared as strings and instantiated as follows…Ĭopy Code Private mstrRightArrow As String Private mstrDownArrow As String…īecause the characters are Unicode, we have to use the ChrW function this prevents us from declaring them as constants.Ī third Unicode character called the black circle character (=) is used to indicate a node without children. When the form loads, we populate the zero level nodes using a suite of queries and a Unicode character to display the closed symbol (4). The node caption and child-count text boxes have their conditional formatting set for highlighting.
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The IsGroup and node-key controls are hidden when the form is displayed. To the right, you can see the IsGroup check-box. You can just see the node-key text box field behind the label that gives the user some instructions. The tree-view form is a simple Access form set in continuous-forms mode. Shows the number of children for that parent. Indicates if the node is closed or expanded. Also note the indentation used to mark off each tree-level. Note that it contains the Unicode character indicating whether the node is closed or expanded (4,6). This is the main field visible in the tree-view. It allows the user to select more than one node and then take some collective action. This is the tick box to the left of each item in the tree-view. So, if your partial key is: strKeys(N) with a value of 1234 OL then Val(strKeys(N)) will return 1234. If you have used a postfix character to make a numeric key unique, then remember that the Val function is really useful to extract the number because it stops reading once it encounters a non-numeric character. Using a pipe symbol allows the key to be disassembled like this… Where child nodes have a numeric key, you may find that you can’t rely on this concatenation being unique so you may have to use a postfix letter such as letter O for Orders or OI for Order Items. Some forethought is needed at the design stage for this key so that it is always unique. You can see that where a second level node has been added, I have used a pipe ( |) symbol to separate the keys. In most instances, you will use the primary keys from the associated tables to create a compound node-key. The field has two functions, first is the primary key and second, because it is a text field, it also acts as the sort key. The fields hold the following information… NodeKey I always shy away from any data model that is not in normal form but in this instance, having everything in one table is easier to display, manage, and debug. When the form loads, the OnOpen event fires and the underlying table is loaded after a selection, it looks like this… In the screenshot of the tree-view (above) zero level nodes are the names of the customers, level one nodes are the order-dates, and level two nodes are the products ordered on the level one date.
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The level of a node means its logical position in the X-Axis. The use of query names with postfix numbers is my way of grouping associated functionality together in the order in which it is used – on large systems you get lost trying to dream up meaningful names! Queries prefixed with hqry mean that this would normally be a hidden query. Tables prefixed with z mean that they are local and, usually, their content is temporary. How Does it Work?Īfter creating an Access database, I incorporated some tables from the Northwind Traders database. The numbers on the right hand side indicate the children belonging to each node – these are optional. The control is designed to allow the user to select an individual node by clicking the check-box or using the arrow keys to open, close, or to move the focus up and down the tree. This control is constructed from an Access form and an underlying local table. As an aside, a really good solution to fixing the problem can be found here. The last instance of the control breaking led me to accept that the best way to avoid the problem from now on would be to write my own. This article addresses the need for a ‘native’ tree-view control constructed with Access tables, forms, and code to get around the problem. From time to time, the control is updated which sometimes leads to applications breaking.
#Microsoft access product code windows#
Microsoft Access does not have a native tree or list view control – we have to rely on a Windows control called MSCOMCTL.OCX to provide these services.