Basic Principle – Descriptive Programming
To the hebrew version of this post
Before we can move on to some of the more advanced subjects, it's probably better if we ensure we're all speaking the same language. So now we'll create a proper base-line for some basic QTP techniques (though even they are sometimes referred to as "advanced"). One of the most profound techniques necessary for advanced QTP usage is "Descriptive Programming" (DP).
General Background
When using DP, we're bypassing the native object repository (OR) mechanism, which may have many advantages (easy to generate and read code, good data organization, etc.), but is extremely not flexible. We'll examine situations in which the OR's advantages are outweighed by the DP's flexibility.
In order to fully grasp how DP actually works, it's best to first understand how QTP's native OR works. The native OR is not some complex and deep mechanism, but rather a simple way of keeping groups of properties and values. To clarify: Whenever we add a certain window to the OR, QTP gathers the window's properties (e.g. – Height="400", Title="New Entity", vbName="NewEntityID"), and stores them as a group of property-value pairs. When QTP runs the script, it compares these properties and values to the "physical" objects, and finds (or fails to find) the object which they describe. Nothing mystical about it.
Usage
In DP, we're "manually" specifying the properties and values by which the relevant object will be identified. This way QTP won't search for the properties data in the OR, but will take it from the DP statement. This can be done in a fast, ad-hoc way, in the very line of the command we want to execute:
The syntax is: Class(PROPERTIESSTRINGS).Command, where PROPERTIESSTRINGS specifies the properties and values for the object's identification. For example:
VBWindow("property1:=value1", "property2:=value2").Click
We can even create an object hierarchy (though once we use DP, we must continue to use DP down the hierarchy):
VBWindow("property1:=value1").VBCheckBox("property2:=value2").Click
Of course "VBWindow" class is just an example for DP with VB objects. DP can be done with SWFWindow, Browser, WinComboBox etc.
The only difference between using DP to using the native QTP OR, is in the content within the class's brackets (in this example: VBWindow()). When using the native OR, we'll put the logical name of the object as defined in the OR. When using DP, we'll put strings describing the properties and values the object will be identified by (structured as "property:=value").
This syntax has the benefit of being shot and quick, but may cause problems if we'll use the object again somewhere else. In this case we'll have to rewrite the all the description strings, making the code less readable, and harder to maintain (i.e., if one of the properties were to change, we'll be forced to make several repairs in different places throughout the code). Luckily, DP allows us to define a static descriptive object, and set its properties once. This way, the script simply refers to the descriptive object:
'----Create Object----'
Dim oDesc
Set oDesc = Description.Create
'----Set ID properties & values---'
oDesc("property1").Value = "value1"
oDesc("property2").Value = "value2"
'----Use and reuse the description object---'
VBWindow(oDesc).Type "Something"
'…
'…
VBWindow(oDesc).Close
'----Release description object---'
Set oDesc = Nothing
We can even combine the two methods:
VBWindows(oDesc).VBCheckBox("vbname:=DPIsCool").Set "ON"
Common uses
(Detailed examples can be found in the attached file)
Well, you might ask yourself why we even bother. QTP's native OR does all these things, is tidier, and up to QTP 9, was the only way to enjoy the benefits of code auto-complete. Well, in some sense, you're right – sometimes, the best way to go is to use the OR, straight up. However, in some cases, DP is preferable by far, and sometimes even the only way to go:
Easy-breezy coding: if we're only going to use an object once or twice, there's no need to use the slow, complex OR, when you can just immediately write the ID string as part of the command. Moreover, with DP you can copy code-snippets between scripts, without having to worry about references to undefined object in the new script.
Inherent dealing with double objects: in case the identification properties and values match more than one object, QTP will through an "object's description matches more than one of the objects currently displayed in your application" error. If we're using the native OR, there no easy way to deal with the situation (we could use a complex Recovery Scenario, but it gets very ugly, very soon). However, DP easily deals with double objects by using the index property. We can add "index:=X" to the description strings (when X is a zero-based counter), and QTP will point to object #X.
Object reference in external functions: when using external functions, you can never count on the relevant object being defined in the calling action's OR. And even if the object is defined there, its logical name might be different, so really, DP remains the only option.
Objects that change hierarchies: sometime an object will appear under a different parent each time (e.g. – a pop-up which appears under the initiating sub-window). In some applications, the only way to work with such objects is with DP.
A common usage which deserves a separate section
Working with a collection of objects: other reasons aside, this is the "Killer Feature" of DP. It makes DP a must for every QTP programmer, and it's hard to overstate its importance and inherent possibilities. According to this concept, instead of working with a single object at a time, we can gather all the objects which answer to our identification properties, and work with them as a collection, serially.
This will be clarified via an example: we're dealing with an unknown number of checkboxes. We don’t know (and don’t care) how they're called, or where they are on the screen – we just need to mark all of them as checked. If we were to do this "the old way", we would have to keep track of each checkbox's properties, and write separate commands that identify each of them, and marks them. With the new objects-collection method, we can ask for all the checkboxes in the screen, loop through them, and mark all of them with a single, easily maintainable command.
This method represents a major improvement, since we've severely reduced our dependence in the application. If the number of checkboxes, their locations, or their names were to change, our code will need zero-maintenance to keep on working. Moreover, in some situations, this method is really the only possible way to go.
This method is implemented with the .ChildObjects command. It receives a DP descriptive object, and returns a collection of the objects that answer to the description. The description can have 0 properties, in which case all the objects will be returned. The following example demonstrates the .ChildObjects command syntax, as well as a pretty standard way to utilize the returned collection:
Dim oDesc
Dim oChildren
Dim i
oDesc = Description.Create
oDesc("micclass").Value = "VbCheckBox"
'----We could've left the oDesc object blank, To get all objects----'
Set oChildren = VBWindow("Main").ChildObjects(oDesc)
'----Now oChildren holds the checkboxs' collection----'
'----Run through the collection----'
For I = 0 to oChildren.Count-1
'----Set the specific checkbox to "ON"----'
oChildren(i).Set "ON"
Next
As you may have noticed, the .ChildObjects command must be executed on a top-level window. This means that you can't get a collection of the top-level windows of an app, only a collection of child-objects In a certain top-level window. This was true until QTP 9, which introduced the Desktop utility object. This allows us to execute Desktop.ChildObjects(oDesc), which returns a collection of top-level windows, so all is well.
More examples and uses are available in the attached file.
Further reading
1. QTP help : Using Programmatic Descriptions
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