how to create barcode in vb.net 2012 Standalone resource dictionary in Visual C#.NET

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Listing 6.2 Standalone resource dictionary
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<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/ presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" > <SolidColorBrush x:Key=" myBrush" Color="Yellow"/> </ResourceDictionary>
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Creating resource dictionaries is pretty easy and also a pretty good idea. We can create multiple styles and resources and then reference them in multiple projects as needed. To use the resources, we do have to put in a reference, sort of like a using statement in C# code. Listing 6.3 shows how to reference a single standalone resource dictionary from within the Window.
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At least not automatically. You could write code at the Window level that asked the Grid for a resource directly.
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Resources
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Adding a new resource dictionary to our project
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Listing 6.3 Referencing a single resource dictionary
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<Window.Resources> <ResourceDictionary Source="Dictionary1.xaml"/> </Window.Resources>
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This works, but it only allows a single reference. We can t, for example, also reference Dictionary2. Worse, we also can t reference one dictionary and have other local resource definitions. Fortunately, we can create a merged dictionary, which combines the contents of multiple dictionaries into one. Listing 6.4 shows how to include multiple standalone dictionaries.
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Listing 6.4 Referencing multiple standalone dictionaries
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<Window.Resources> <ResourceDictionary> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="Dictionary1.xaml"/> <ResourceDictionary Source="Dictionary2.xaml"/> </ResourceDictionary.MergedDictionaries> </ResourceDictionary> </Window.Resources>
The MergedDictionaries tag allows for any number of dictionaries to be referenced and then merged together. A dictionary can be a reference to a standalone dictionary or can be a dictionary declared directly in the XAML. The latter is how we go about including references to standalones combined with local resources, as you can see in listing 6.5.
Resources, styles, control templates, and themes
Listing 6.5 Referencing a standalone dictionary and local resources
<Window.Resources> <ResourceDictionary> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="Dictionary1.xaml"/> <ResourceDictionary> <SolidColorBrush x:Key="myBrush" Color="Red" /> </ResourceDictionary> </ResourceDictionary.MergedDictionaries> </ResourceDictionary> </Window.Resources>
You can see how the second dictionary only contains resources b including the brush we ve been working with. This notation is a little bulky, and it would be nice if Microsoft had provided some sort of reference tag that could be put inside a regular resource dictionary instead. Hopefully, when they get around to building a GUI editor for resources, they will make it easy to reference standalones along with the local resources. By the way, you may have noticed that there are now two definitions for myBrush one local and one in the standalone dictionary. The way the conflict is handled is fairly egalitarian the last one defined wins. In listing 6.5, the local version is listed second, so the border will be red. If we turn around the XAML
<ResourceDictionary.MergedDictionaries> <ResourceDictionary> <SolidColorBrush x:Key="myBrush" Color="Red" /> </ResourceDictionary> <ResourceDictionary Source="Dictionary1.xaml"/> </ResourceDictionary.MergedDictionaries>
then we d get the yellow version defined in Dictionary1.
Using resources from code Anything we can do in XAML, we can also do in code.2 XAML is a shortcut to code the appropriate objects get constructed based on the XAML, and then their code is executed. This is true for resources as well. The resource dictionary is available for each object, and can be referenced and modified as needed. Let s start with accessing existing resources. Resources are available via the Resources property of framework elements and framework content elements. Resources are exposed as a collection, so we can add, iterate, and do other collection-y things. But, when we look for resources, we generally don t hit the collection directly. We use the FindResource method instead:
button9.BorderBrush = (Brush)FindResource("myBrush");
This method searches resources in the same way as if we had put the declaration in XAML. It searches the local resources first, then steps up the chain to the parent, and
Although there are a few things that would be really painful to do in code.
Resources
so on. If it fails to find the resource, then it throws an exception the same as the XAML version. If we don t want the code to throw an exception if it fails to find the resource, there s another version of FindResource called TryFindResource:
button9.BorderBrush = (Brush)TryFindResource("myBrush");
This version returns null if the resource isn t found. If null isn t a supported value for the particular property, then we end up with an exception anyway. For brushes in general, this isn t a problem null means that the value isn t set, so go with the default behavior. Adding and updating resources is as simple as updating any dictionary. For example, to change the myBrush brush to a different color, we write:
this.Resources["myBrush"] = new SolidColorBrush(Colors.Green);
The this in this case is the Window, so we re updating the Window s resources. We could as easily update the resources for the Grid or one of the buttons. By the way, it s pretty easy to update the Application s resources as well the Application object has a static property that exposes the current application:
Application.Current.Resources["myBrush"] = new SolidColorBrush(Colors.Green);
One caveat here is that we re updating a specific resource dictionary. So, if the brush you re using is in the application and you set the value on the Window s resource dictionary, you end up with two different versions of the brush at two different levels. This may or may not cause problems, depending on your goals. In the examples so far, we ve retrieved values from the resource dictionary and set a property as a one-off thing. It s more important to update the proper resources if you want properties to change dynamically when the resource value changes.
Dynamic resources Much of the time, when you set the value of a property, you re done. The background is going to be blue, so you set the background to blue. But there are times when it isn t a one-off thing. For example, suppose you want to set the background based on a user preference. In yon olden days, when the user changed the preference, the fastidious programmer would write code to step through all the UI and update the value, or destroy the UI elements and re-create them with the new color.3 To plan for a lot of such changes, you might build some sort of dictionary for looking up colors. You could then update the dictionary and tell all the UI elements to redraw themselves, causing them to look up the new color. Because all the built-in elements wouldn t know about your dictionary, you d have to build support code to pass on values, and you d have to make sure that every color that might change was appropriately redirected. Quite a bit of work.
The lazy programmer would tell the user to restart the application, but the rest of us would be required to heap scorn upon such an approach.
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