113: Three Bitmap Resource Names from the ShowBitmap Manifest in .NET

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Listing 113: Three Bitmap Resource Names from the ShowBitmap Manifest
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mresource public ShowBitmapSPADEBMP { } mresource public ShowBitmapCUPBMP { } mresource public ShowBitmapHEARTBMP { }
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Visual Studio NET creates an untyped resource from an external file when you add the file to a project and assign a build action of Embedded Resource The default build action for bitmap files, Content, allows the bitmap file to be downloaded with a program but as a separate file and not as
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Figure 112: The Settings to Turn CUPBMP into an Embedded Bitmap Resource
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an embedded resource Figure 112 shows the Visual Studio NET settings to turn the file CUPBMP into an embedded bitmap resource The name of the resource is ShowBitmapCUPBMP, which we need to know to access the resource from our code You can access an embedded resource by calling a method in the Assembly class, named GetManifestResourceStream24 As suggested by the method name, the return value is a Stream object; more precisely, you are provided a MemoryStream25 object You can use all of the elements associated with a Stream-derived class (including the ability to query the resource length, which is the same as the resource input file) to seek a location in the stream and to read bytes (the CanSeek and CanRead properties are both set to true) In keeping with the read-only nature of Windows resources, you cannot write to a resource stream26 (CanWrite returns false) The code fragment that is shown in Listing 114 shows two methods from the ShowBitmap sample program These methods are helper routines to handle the initialization and cleanup of resource-based bitmaps The LoadBitmapResource method creates a bitmap from a resource; the DisposeBitmap method provides the cleanup
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24 SystemReflectionAssemblyGetManifestResourceStream 25 SystemIOMemoryStream 26 In contrast to an Apple Macintosh resource fork, which supports both read and write
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What Can Go into an Untyped Resource
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This chapter provides an example of putting a bitmap into an untyped resource But this is not the only type of resource you can create You can put any custom data into untyped resources, which can then be used to access the data at runtime When you request an untyped resource, you are provided with a Stream object that you can use as you wish You might, for example, read a resource into an array of bytes and then parse those bytes in whatever way your application needs Such resources can be any readonly data that your program needs: tax tables, sports scores, or as we show in the ShowBitmap sample program a set of bitmaps A benefit of using custom resources is that we have access to data we need at runtime But when we are not using that data, it does not occupy scarce program memory This makes custom resources a useful tool in our toolkit for building memory-wise programs
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Listing 114: Creating Bitmaps from Untyped Manifest Resources
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private Bitmap LoadBitmapResource(string strName) { Assembly assembly = AssemblyGetExecutingAssembly(); string strRes = "ShowBitmap" + strName; Stream stream = assemblyGetManifestResourceStream(strRes); Bitmap bmp = null; try { bmp = new Bitmap(stream); } catch { } streamClose(); return bmp; } private void DisposeBitmap(ref Bitmap bmp) { if (bmp != null) { bmpDispose(); } bmp = null; }
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The LoadBitmapResource method creates a bitmap by opening a resource stream and uses data read from that stream to create a bitmap This method gets a reference to the program s assembly by calling a static method in the Assembly class named GetExecutingAssembly After creating a bitmap, the stream can be closed Once a bitmap has been created, it is self-contained and needs no external data That is why we can close the stream once the Bitmap object has been created The DisposeBitmap method deletes the bitmap to free up its associated memory It does this by calling the Dispose method for a Bitmap object There are only a few situations in which it is mandatory to call the Dispose method27 Sometimes, however, it is still a good idea even if it is not, strictly speaking, required Bitmaps can be large, so we suggest you consider explicitly deleting bitmaps, as we have done in our sample Among the factors to consider are the size of your bitmaps and the number of bitmaps We suggest that you explicitly delete bitmaps when you have either many small bitmaps or a few large bitmaps We call our two methods using code such as the following:
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private void mitemResourceCup_Click(object sender, EventArgs e) { DisposeBitmap(ref bmpDraw); bmpDraw = LoadBitmapResource("CUPBMP"); Invalidate(); }
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After cleaning up the old bitmap, we create a new bitmap and request a Paint event by calling the Invalidate method Next, we discuss image file size, and how to save memory by changing the format you use for your images
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