Xamarin Tips and Tricks – Clearing Lists in C#

(Originally published 4/3/17)

Sometimes, using the built-in Clear() function on C# Lists may not always work. For example, I needed to clear a list of all its contents every time I returned to a Page view. Using the Clear() function was not clearing the list properly and thus resulting in the Page crashing. Although it may not always be the most obvious solution, if you are every getting IndexOutOfBounds exceptions when dealing with clearing a list, you may want to try doing it the old fashioned way – using a for-loop to traverse the List from head to tail and using the RemoveAt function to remove the object. Here is a snippet of the function below:

	public void ClearList(List myList)
	{
	for(int x = myList.Count – 1; x >= 0; x—)
	{
	myList.RemoveAt(x);
	}
	}

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ClearList.cs

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This simple function can solve some major issues regarding clearing of a list. This can really be applied to any language in any situation where the built in clear function is not doing the proper job. Thanks for reading, and stay tuned for more updates.

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Xamarin Tips and Tricks – Compressing Videos in Xamarin.Forms Projects

(Originally published 3/29/17)

Today I will be starting a series of Xamarin programming tips and tricks that I have learned from different projects I have worked on. Lets kick this off with platform specific video compression in Xamarin.Forms. Since media encoding is done differently on iOS and Android, we need to write different solutions for Forms projects. We will be taking a look at iOS media compression today. Our media will be picked using Xamarin’s Media Plugin (Plugin.Media), which delivers the picked media in a MediaFile object. We will then pass this object into our compression method which will then send it back out as a file stream. You can view a gist of the method involved below:

	public async Task<Stream> CompressVideo(MediaFile file)
	{
	string exportPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
	string exportFilePath = Path.Combine(exportPath, "compressed_video.mp4");
	System.Diagnostics.Debug.WriteLine("Export path: " + exportPath);
	System.Diagnostics.Debug.WriteLine("Export file path: " + exportFilePath);
	var asset = AVAsset.FromUrl(NSUrl.FromFilename(file.Path));
	AVAssetExportSession export = new AVAssetExportSession(asset, AVAssetExportSessionPreset.MediumQuality);
	System.Diagnostics.Debug.WriteLine("Created export object");
	export.OutputUrl = NSUrl.FromFilename(exportFilePath);
	export.OutputFileType = AVFileType.Mpeg4;
	export.ShouldOptimizeForNetworkUse = true;
	System.Diagnostics.Debug.WriteLine("Preparing to export");
	await runExportAsync(export);
	Stream exportStream = File.OpenRead(exportFilePath);
	System.Diagnostics.Debug.WriteLine("Stream read from file");
	return exportStream;
	}
	private async Task RunExportAsync(AVAssetExportSession exp)
	{
	await exp.ExportTaskAsync();
	if (exp.Status == AVAssetExportSessionStatus.Completed)
	{
	System.Diagnostics.Debug.WriteLine("Finished export");
	}
	}

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gist.cs

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Your MediaFile will have its uncompressed mov file taken out of it, encoded again with higher compression at a lower resolution using the native AVAssetExportSession, and sent back out as a stream. All of this runs in async and is fast on new(ish) iOS devices. You can change the amount of compression applied by modifying the export preset as well as change what type of object the file gets sent back out as (a stream is the easiest to work with especially if you are planning on uploading the file to a web service). These methods can be easily dropped into a platform specific class using a dependency service to call upon it when needed. Also note that you will have to create a public interface for this as well.

 

Fixing Raspbian apt source list

(Originally published 3/28/17)

Updating via apt suddenly stopped working for me today on both my Raspberry Pis with one on Jessie and the other one on Wheezy (it got stuck on waiting for headers). Took me a while before I figured the mirror director was the problem (I guess there is a outage with one of the mirrors). Inside the apt source list, commenting out the mirror director entry and replacing it which archive.raspbian.org fixed it.