An introduction to PowerBoots

Please excuse me if I start by just copying the basic ideas of the Shoes Tutorial, but I figured that since PowerBoots is inspired by Shoes, that was as good a place as any to start. PowerBoots (or just “Boots”) is a PowerShell 2.0 module with functions for writing Windows Presentation Framework (WPF) applications in the PowerShell scripting language. You should get the latest version of PowerBoots before continuing, and install it by putting the “PowerBoots” folder in one of your “Modules” folders (list them by typing $Env:PSMODULEPATH in PowerShell v2).

Don’t forget to start PowerShell.exe with the STA parameter (This is no longer required in PowerBoots 0.1).

Did I hear someone ask what is WPF? It was introduced as part of .Net 3.0 (and vastly improved in .Net 3.5), so you can expect to find it preinstalled on computers from Vista on, and of course you can download and install it on XP if it’s not already installed. The only thing you really need to know about WPF for the purposes of this tutorial is that it is the new GUI toolkit for .Net, and that it is container based — you put elements into other elements to control the layout, rather like HTML and Java Swing… you can pick up the rest as we go along.

A simple Boots program

The parenthesis ( and ) are a container, so the button is “in” the Window. You can also pass a ScriptBlock instead, which works basically the same way. Of course, this is a bit uglier than the Shoes syntax, so lets see if we can’t clean it up some. The -Content parameter is positional, so the first non-named argument you pass will be used for that. The same is true for the -Children parameter of panels, and in fact, each of the other similar parameters: Items, Blocks, and Inlines.

We have used a function New-BootsWindow which has an alias Boots. Boots takes all the same parameters as the Window function mentioned previously, but it uses slightly more useful defaults, and has a few other major benefits as well, the first of which is that it automatically “shows” the window, and the second is that it supports an -Async parameter which allows the window to come out in a new thread so that you can continue using PowerShell while the window remains alive and responsive. There is one catch: New-BootsWindow cannot take it’s content on the pipeline (the old function, now renamed “Out-BootsWindow” can take pipeline content, but is a script function, and requires -STA mode) — you have to specify it as a ScriptBlock. So now that we know this, we can rewrite our first example like this:

Just for the record, the simplest Boots program would just be a simple popup dialog to put some text in a Window, like: Boots { $msg } …

We can put controls in a stack

StackPanels are awesome. So are WrapPanels. Try that code with a WrapPanel instead of a StackPanel and see what the difference is. This brings up another point: those positional parameters we mentioned earlier: Content, Children, Items, Blocks, and Inlines, are also set to accept the value from the pipeline. Not only that, but they are intelligent about whether or not the content model accepts multiple items! So we can actually rewrite that script like this, and get the same results:

Now we’re really onto something! For most of the rest of these examples, I’m going to stick with the former syntax, because with the indenting and parenthesis, it’s much easier for you to follow, especially if you’re not already familiar with WPF. For instance, check out what this does:

Ok, lets see some formatting

To scoot the buttons out from the edge we can use margins or padding: margins go on the outside of containers, padding goes on the inside.

So you see, the pink background is on the StackPanel, which has a (white) margin around it. If you wanted the whole background of the window to be pink, you would need to set the background of the Window instead of the StackPanel.

Time for some artwork

In Boots, everything always starts out white, and you must position things based on the container. You can see that the Margin can be specified as a single value as in the previous example, or as separate values for Left, Top, Right, Bottom. Oddly, to satisfy PowerShell’s type-casting, you have to quote them so they’re a single comma-separated string, instead of four separate values.

Some more advanced drawing

We use a Canvas for this because it can contain multiple items which are all absolutely positioned. Unlike other containers, it doesn’t automatically expand to contain it’s children, so you typically have to set it’s size.

We also have to set the Stroke and Fill. These are the two colors that make up every object, if we don’t set them, they default to white. The StrokeThickness controls the line thickness. Notice that we positioned the Rectangle by using the Margin, and positioned the arrow, which we built using a Polygon, based purely on the x,y coordinates of the points. The available shapes are Ellipse, Line, Path, Polygon, Polyline, and Rectangle. You can, of course, make any shape you want to with the Polygon.

There are other more advanced shapes available in external libraries, and we can even do 3D, use gradient or image fills…

We can even get images straight off the web

Boots loads the image on a background thread, and caches it in memory, so the window will show up and be responsive while you’re waiting for the image, and because we’ve specified -Async, you can actually continue using PowerShell while the image loads. Note: it will load much faster the second time you run that script.

Typography

PowerBoots doesn’t try to create a full set of typography-specific top-level elements the way Shoes does, because we are based on WPF, which has a far more powerful typography system available than any we’ve ever used. So instead of having a bunch of named elements like banner, and title, and caption, and para and whatnot, we have controls based on how much text you want to put in them, and how much formatting you want to apply: Label is simplest, TextBlock supports limited text formattings, and FlowDocument supports full rich content. And of course, Hyperlink supports clicking

For the typography elements, the content model changes a bit. There are basically two types: Inline and Block elements. The TextBlock Content Model is similar to that of a FlowDocument, it is actually a type-restricted “Items” container. Instead of being able to have anything as content, it can only contain Inline flow content elements such as AnchoredBlock, Bold, Hyperlink, InlineUIContainer, Italic, LineBreak, Run, Span, and Underline, and it will create a run automatically if you just put a text string in it.

Note: If you want support for the full document model (which allows Paragraphs and Lists), you need to use a FlowDocumentReader, FlowDocumentPageViewer, RichTextBox, or a FlowDocumentScrollViewer ... there’s lots more information about those on msdn.

Events

If you were paying attention to that previous example, you’ll notice we just introduced event handling. Event handlers in PowerBoots are specified in much the same way that Properties are. Their parameter names always start with “On_” and they take a script block. The Hyperlink element in a WPF window doesn’t automatically open a browser (because you can use it to change “pages” in a WPF application), so to make simple web links work, you have to handle the “RequestNavigate” event as shown above.

In order to update your user interface when an event triggers, you’ll need to have a variable that points at the control(s) you want to affect. You get a $this variable for free which points at the object that caused the event (eg: the Hyperlink in our previous example), but otherwise you need to handle this yourself. You can do that one of two ways: you can set a variable the way you normally would, and then use the variable in the form, or you can specify the variable name using the -OutVariable parameter. Personally I prefer the latter, as it messes up the flow of code less, but it has the downside that the output variable is always an array, even when there’s only one item.

I’ve made these examples slightly more complicated than they had to be to demonstrate some best practices. When the Window is closed, the Out-Boots function returns the $BootsOutput variable — so if you want to output something from your gui, you need to set that variable. You can, of course, access global scope variables using the scope prefix $global:variableName, so you can set many different variables which you read later in your script. The catch is, sometimes the variables have to be explicitly set to script or even global scope in order to refer to the same variable in all of the event handlers…

However, if you want to have this block of code actually output something into the pipeline, you’ll always want to use the $BootsOutput variable. You can do that directly, the way the example above does, or you can simply use Write-Output! Inside the Out-Boots function, he Write-Output cmdlet just appends to the $BootsOutput variable … so it works pretty much exactly the way you would expect it to.

The first example outputs just the count of how many times you clicked. The second outputs a series of numbers from 1 to however many times you click. It’s your choice of how to work with it.

We can have fun with colors

Boots gives you access to all the capabilities of the Windows Presentation Framework, but in some cases that comes at a cost, because we haven’t simplified their composability. So we have RadialGradientBrush and LinearGradientBrush, but you have to specify the GradientStops etc …

We also have

So what does an InputBox look like?

Well, the simplest possible input box is just a TextBox, with the Width set (if you don’t set the Width, a TextBox will adjust to fit it’s contents, which can be really distracting). All you need to do is this:

Of course, the problem with that is that it pops up this rather confusing window, when what we really wanted was a prompt, and an “Ok” button, and some event handling to make the thing behave the way we expect it to. So lets try our first complicated form.

I’ll warn you ahead of time of one thing I’m going to do here. I’m using the “Border” element to apply a colored border to the StackPanel (because it doesn’t have it’s own border parameters), but then I’m also using the WindowStyle and AllowsTransparency properties to remove the normal window chrome, creating the bare little popup you see in the screenshot. I handle the mouse down event on the main window to allow the user to drag the window around by clicking anywhere on it (except in the TextBox or on the Button, of course). Now it looks slick, and —you know— it works!

Hopefully you can follow that, although it’s obviously over the top . We handle the KeyDown event on the TextBox (if the Key is the Return key), and we also handle the click on the Button. In both cases, we’ll write out the text that was entered, and use the special $BootsWindow variable to close the window. We also handle the Load event for the window, to make sure the focus is on the TextBox, so you can just start typing.

A final example

I’ve got quite a few more examples I want to show off in part two of this tutorial, but to get you thinking about ways to integrate this with your routine tasks, and give you some ideas of what you can do with what you know already, let me give you this example of browsing photos, with a visual indication of how big the image file is. Of course, the point is that you could be visualizing, you know … anything.

Notice that I had to manually handle the concept of a double click, because StackPanels don’t have a Click or DoubleClick event, just MouseDown and MouseUp. I could have stuck the stackpanel into something that does, but there’s really no need. Also, the [Diagnostics.Process]::Start is the equivalent of typing the name into the run dialog. I’m just executing the jpg, which makes it open in the default editor. It’s just a sample, after all.

End note

The current version of Boots does not add threading support, which means that when you run something through Boots, execution of your script stops until the window is closed. You can get around this somewhat in various different ways, but future releases will support running the WPF window in a separate thread, and even communicating to it … at the expense of a slightly different syntax. If you need that functionality, feel free to let me know … I could use some motivation.

I hope you’ve enjoyed this tour through PowerBoots, and will be able to start applying it for fun and profit.

looking for a … guide to putting together an advanced function that is visible and usable every time I start Powershell. By visible I mean that when I do a ‘get-command’ I want my [advanced function]s to be listed alongside all the regular cmdlets. What makes that possible? ... what do I need to do to make that happen? Whats the difference between an [advanced function] and a module?

There are lots of articles on the Microsoft PowerShell team blog about both topics, but it seems there’s not really been any sort of step-by-step written, so I posted this to the newsgroup, and since the person who asked the original question said he found it useful, I figured I’d share it here…

An Aside: Advanced Functions vs. Modules

Advanced functions and script modules are unrelated topics. A script module could have nothing but old PowerShell 1 -type functions, hypothetically, it could even not have any functions at all. Advanced functions can be defined in a plain .ps1 script, in your profile, or by typing them in on the command-line, etc. The two things are essentially unrelated except for both being new features in PowerShell 2.0.

How To write an Advanced Function

Step 1: Have something you want to do in a function.

I can’t emphasize enough how important it is that you should have a specific goal here. Writing a script for a specific purpose is much easier, because you don’t have to think about whether or not specific features are necessary, etc.

For the purposes of this example, I want a function to start executables and return me the process object (so I can wait for it to finish, or whatever). I will call it Start-Process.

Step 2: Write a first step for the logic of your function.

Be sure to specify the parameters using the functionName{Param(...)} syntax rather than functionName(...){}, then you will convert it to an advanced function by adding [CmdletBinding()] on a line right before the Param:

Step 3: Start writing documentation and auto-help, including your parameters.

Step 4: Exploit advanced features by marking up your parameters.

In my case, I had a look at the signature of the start method by running [Diagnostics.Process]::Start.OverloadDefinitions and discovered that it can take credentials too. So I wanted an optional credential parameter. I specified it without a position, and made it part of a non-default parameter set.

I also wanted the params parameter to just take any additional parameters which I pass to the function, and pass them on to the process that I’m starting.

Finally, I wanted the “App” parameter to be able to come from the pipeline. Specifically, I wanted to be able to pass the output of Get-Command or Get-ChildItem to it. In order to enable that, I defined an alias on it to the relevant properties of the objects which come from those two commands

Hopefully you’re getting the idea of what’s possible here …

Bonus Step: Make the function be automatically defined

To be honest, there are a lot of ways to do this, here’s a few:

Option 1. Define it in your Profile.

Include the full text of the function in your Profile.ps1 script or Microsoft.PowerShell_profile.ps1 … just run notepad $Profile and paste the whole function in at the top, then save.

Option 2. Dot-source it in your Profile.

Save the function into a script file, e.g.: “StartProcessFunction.ps1” in your DocumentsWindowsPowerShell folder (next to your profile script) then put the line: . StartProcessFunction.ps1 into your profile script to dot-source it. Using the dot causes the script to be loaded into the context as though you had put the contents of the script in, instead of the dot-source line.

Option 3. Import this function from a script file.

This is basically the same as Option 2, except instead of “.” you can use Import-Module. The Import-Module cmdlet, when used on a file with the .ps1 extension, is basically the same as dot-sourcing it, so there’s not a whole lot of benefit over dot-sourcing in this case.

Option 4. Put the function in a module.

You should only do this if you think you might want to add additional functions to the module. For instance, lets say you want to write a few other functions for working with process objects. If you put them together in the same module (say: “ProcessUtility”) they can share script-scoped variables or private functions, and can be identified as being part of the same module using the Get-Command -Module ProcessUtility command.

If you just have the single function, there’s really no point in changing it to a Module, but I’m not aware of any downside, either.

Option 4a. Make a module by just saving as a .psm1

All you do is save the function into a module file, e.g.: “ProcessUtility.psm1” in your DocumentsWindowsPowerShell folder and then put the line: Import-Module ProcessUtility.psm1 into your profile script.

Option 4b. Make a module folder.

This is by far the most extensible way to create modules. You paste the function into “ProcessUtility.psm1” and then save it into a folder “ProcessUtility” which must be created in one of your module folders. You can figure out where the module folders are by checking $Env:PSMODULEPATH — the normal spot is your DocumentsWindowsPowerShellModules.

Once that’s done, you can import with the simpler command Import-Module ProcessUtility without any extension.

The nice thing about creating the folder is that you can put any additional resources in that folder with it, and get at them using the $PsScriptRoot to define the folder. You can even add additional functions by putting them in separate files (which you can Import-Module from the main file, or you can define using a .psd1, but that’s another article).