How to use an event argument outside an event

Question

First of all, I want you all to know that I started learning C # as my first programming approach, and therefore I am the absolute hobbiest beginner who started coding 2 months ago, so please come with me.

So what I'm trying to do is create a custom download application. It all works, except for the "Download All" button, which cannot select the variable "percent1" from the "DownloadProgressChangedEventArgs". I created it before the mainForm constructor, but it will not read the changed value.

Here's the code, partially divided, since most of it is not relevant to the question:

public partial class Main : Form { //Variables (not all, just the one im having issues with) private double percentage1; //Main form constructor public Main(){...} //Download File Async custom method public void DldFile(string url, string fileName, string localPath, AsyncCompletedEventHandler completedName, DownloadProgressChangedEventHandler progressName) { WebClient webClient = new WebClient(); webClient.DownloadFileAsync(new Uri(url), localPath + "\\" + fileName); webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(completedName); webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(progressName); } //Button 1 click event to start download private void btnDld1_Click(object sender, EventArgs e) { if (url1 != "" && Directory.Exists(localPath1)) { _startDate1 = DateTime.Now; DldFile(url1, fileName1, localPath1, completed1, progress1); } //took out the try/catch, other ifs to try and cut it down } //Download Progress Changed event for Download 1 public void progress1(object sender, DownloadProgressChangedEventArgs e) { percentage1 = e.ProgressPercentage; //THIS IS WHERE I WAS EXPECTING TO UPDATE "percentage1" progressBar1.Value = int.Parse(Math.Truncate(percentage1).ToString()); } //Button that starts all downloads click event where all my problems are at the moment private void btnDldAll_Click(object sender, EventArgs e) { //The progress bar that should let me know the global status for all webClients progressBarAll.Value = ( int.Parse(Math.Truncate(percentage1).ToString()) + //HERE IS MY PROBLEM int.Parse(Math.Truncate(percentage2).ToString()) + //HERE IS MY PROBLEM int.Parse(Math.Truncate(percentage3).ToString()) + //HERE IS MY PROBLEM int.Parse(Math.Truncate(percentage4).ToString()) + //HERE IS MY PROBLEM int.Parse(Math.Truncate(percentage5).ToString())) / 5; //HERE IS MY PROBLEM //Checks if the link exists and starts it from the download button click event if (url1 != "") { btnDld1.PerformClick(); } //Continues for url2, 3, 4, 5 and else } } 

So, this is the shortest way that I have found to inform you that I am trying to shoot, if something is missing there, please let me know, I will try to add any information as quickly as possible.

I tried to create an instance of "progress1" to try to use the percent1 variable, but it did not work. I tried to do the same with webClient but did not work. I used google search and stackflow to no avail. So I'm not sure if the question is too stupid, or is there another way to look at a problem that completely leaves my mind.

Thus, the main problem is updating the percent1 variable and using it. There are other problems associated with calculating "progressBarAll.Value" that will be resolved when I can get the correct value. So no need to worry about it if you see it.

I am so sorry for the long post, but I'm not sure where the problem is, so I had to give you more information to make sure that I did not mess up elsewhere.

Happy coding; D

Answer 1

Try not to think about 'using event arguments outside the event'. Think about updating the state of your form.

Use properties to simplify the update logic:

 public partial class Main : Form { private double percentage1; private double percentage2; private double percentage3; private double percentage4; private double percentage5; private double Percentage1 { get { return this.percentage1; } set { this.percentage1 = value; this.UpdatePercentageAll(); // this will update overall progress whenever the first one changes progressBar1.Value = GetValueFromPercentage(value); } } private double Percentage2 // same code as for Percentage1 void UpdatePercentageAll() { this.PercentageAll = (this.Percentage1 + this.Percentage2 + this.Percentage3 + this.Percentage4 + this.Percentage5) / 5; } static int GetValueFromPercentage(double percentage) { return (int)Math.Truncate(percentage); } double percentageAll; private double PercentageAll { get { return this.percentageAll; } set { this.percentageAll = value; progressBarAll.Value = GetValueFromPercentage(value); } } //Download File Async custom method public void DldFile(string url, string fileName, string localPath, AsyncCompletedEventHandler completedName, DownloadProgressChangedEventHandler progressName) { WebClient webClient = new WebClient(); webClient.DownloadFileAsync(new Uri(url), localPath + "\\" + fileName); webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(completedName); webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(progressName); } //Button 1 click event to start download private void btnDld1_Click(object sender, EventArgs e) { if (url1 != "" && Directory.Exists(localPath1)) { this.StartDownloadFile1(); } //took out the try/catch, other ifs to try and cut it down } void StartDownloadFile1() { this.Percentage1 = 0; _startDate1 = DateTime.Now; DldFile(url1, fileName1, localPath1, completed1, progress1); } //Download Progress Changed event for Download 1 public void progress1(object sender, DownloadProgressChangedEventArgs e) { this.Percentage1 = e.ProgressPercentage; // update property, not field //this will be done in property setters //progressBar1.Value = int.Parse(Math.Truncate(percentage1).ToString()); } // then add similar code for other download buttons //Button that starts all downloads click event where all my problems are at the moment private void btnDldAll_Click(object sender, EventArgs e) { //Checks if the link exists and starts it from the download button click event if (url1 != "") { this.StartDownloadFile1(); } //Continues for url2, 3, 4, 5 and else } } 

I would reprocess the code even more, but I think it will be easier for you to understand if the code is suitable for the original.

The basic idea is to create a set of related properties that work like mathematical functions. When writing PercentageX properties, I say "let PercentageAll average all percentages." Then I have each update to download, which has its own progress. As soon as any progress is updated, it updates the average value, and I do not need to remember that inside the event handler is processed changes.

And the last point is updating progress indicators from percentage properties. This is pretty simple: after changing the percentage, I need to update the panel. If so, why write something like

 this.Percentage1 = x; this.progressBar1.Value = (int)Math.Truncate(x); 

In this case, I have to remember everywhere that after changing Percentage1 I need to update the panel. And in my example, I just create a strict rule for what is in only one place and works every time. So I just can’t forget it. And if I need to change the rule, I need to change only one place, so I cannot be mistaken.

The technique that I demonstrate can be expressed as a well-known rule: "one rule - one place", which means that you should try to have only one place in the code that expresses each logical rule that exists in your program. This is a very important idea, I suggest you study and use it.