C# visualstudion windows form graphics chart

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VS2017

Hello,

I just created a Graphics Chart by code that works with an OlrDb access base and works well.

C#

Chart Graph_121 = new Chart(); // Créer un Chart vide
ChartArea ChartArea121 = new ChartArea(); // ChartArea (zone graphique)
Graph_121.ChartAreas.Add(ChartArea121);  // Ajoute le Chart Area à la Collection ChartAreas du Chart
Series series121 = new Series();  // Création serie (qui contiendront les DataPoints)

My question is the following :

In the same form I want to add a button and delete with the method Clear my Chart, how to do?

Nothing works :

C#

Graph_121.Clear();
ChartArea121.Clear();
series121.Clear();

The name Graph_121 does not exist in the current context !
Can we declare Graph_121, ChartArea121, series121 in public?

thank you

What I have tried:

C#

  Control Page_Principale = Graph_121.Page_Principale;
Page_Principale.Controls.Remove(Graph_121);

Graph_121.Clear();
ChartArea121.Clear();
series121.Clear();

Posted 15-Mar-19 3:52am

LSB71

Updated 15-Mar-19 21:34pm

Dave Kreskowiak

v2

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Comments

Richard MacCutchan 15-Mar-19 11:00am

Make sure your variable is not declared inside a method, when it is referenced in other methods.

Richard Deeming 21-Mar-19 14:42pm

Based on the additional information in your not-a-solution solution, you've declared fields at the top of your class, and you've then declared local variables in one method which have the same name as those fields. You assign values to the local variables, but you never assign anything to the fields.

You're effectively handing an envelope to someone called "Bob", and then walking up to a different person who is also called "Bob" and expecting them to have your envelope.

2 solutions

Solution 2

Hello, 
Thanks for your help. I just created a method like this:

C#

  public void MyGraph_121()
        {
            string CentreAnnee = Filtre_Cbo_Annee.Text;

            Chart Graph_121 = new Chart();
            ChartArea ChartArea121 = new ChartArea(); 
            Graph_121.ChartAreas.Add(ChartArea121); 
                      Series series121 = new Series
            {
                IsValueShownAsLabel = true, 
                ChartArea = "ChartArea1"      
            };  
            
            Graph_121.Series.Add(series121); 

// rest of the code

      }

Then I said at the top of my page like this:

C#

public int i1, i2, i3, i4, i5, i6, i7, i8, i9, i10, i11, i12, i13, i14;
        public string CentreAnnee;
        public ChartAreaCollection Graph_121, ChartArea121, series121;

Then once the graph displayed I test with this button:

C#

private void button1_Click(object sender, EventArgs e)
{

    ChartArea121.Clear();
    series121.Clear();
    ChartArea121.Clear();
}

I have as an error message:

C#

System.NullReferenceException : 
'Object reference not set to an instance of an object.'
ChartArea121 was null.

How to declare Chart items?

C#

public ChartAreaCollection Graph_121, ChartArea121, series121;

Is it objects, string does not go, int either?

thank you

Posted 15-Mar-19 21:34pm

LSB71

Comments

Richard Deeming 21-Mar-19 14:40pm

If you want to update your question to add missing information, click the green "Improve question" link and edit your question. DO NOT post your update as a "solution" to your question.

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Gerry Schmitz · Accepted Answer · 2019-03-15T05:03:00

Solution 1

Looks like your "chart" is going "out of scope" if you created it "by code" as above.

Define your chart "at the class level" as a "private or public" member so that different parts of your program can "see" chart and not just the method that first created chart (as a "local" variable).

Posted 15-Mar-19 5:03am

Gerry Schmitz