Null reference exception
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Hi, when i run this code i get a null-reference exception at the last line of code. I don't know why this happens, because i first add the node and it IS there. I looked in the debugger. Does someone know a solution?
foreach (DateTime d in daten) { if (treeView1.Nodes.Find(d.Month.ToString(), false) != null) { treeView1.Nodes.Add(new TreeNode(d.Month.ToString())); } treeView1.Nodes[d.Month.ToString()].Nodes.Add(new TreeNode(d.Date.ToShortDateString())); } -
Hi, when i run this code i get a null-reference exception at the last line of code. I don't know why this happens, because i first add the node and it IS there. I looked in the debugger. Does someone know a solution?
foreach (DateTime d in daten) { if (treeView1.Nodes.Find(d.Month.ToString(), false) != null) { treeView1.Nodes.Add(new TreeNode(d.Month.ToString())); } treeView1.Nodes[d.Month.ToString()].Nodes.Add(new TreeNode(d.Date.ToShortDateString())); }It will be easier to see what's going on if you break out that last line of code as follows: TreeNode node = treeView1.Nodes[d.Month.ToString()]; TreeNode newNode = new TreeNode(d.Date.ToShortDateString()); node.Nodes.Add(newNode); This will allow you to check state as you step though in debug mode. When you put so much into a single line, it can be much less obvious what is breaking.
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Hi, when i run this code i get a null-reference exception at the last line of code. I don't know why this happens, because i first add the node and it IS there. I looked in the debugger. Does someone know a solution?
foreach (DateTime d in daten) { if (treeView1.Nodes.Find(d.Month.ToString(), false) != null) { treeView1.Nodes.Add(new TreeNode(d.Month.ToString())); } treeView1.Nodes[d.Month.ToString()].Nodes.Add(new TreeNode(d.Date.ToShortDateString())); }if d is null from daten then d.Month will fail; Also, treeView1.Notes[someString] may return null as well but it is most likely the d;
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if d is null from daten then d.Month will fail; Also, treeView1.Notes[someString] may return null as well but it is most likely the d;
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Ennis Ray Lynch, Jr. wrote:
but it is most likely the d
Not so very likely... The variable d is a DateTime structure, and can't be null.
--- single minded; short sighted; long gone;
Since daten is not defined in could very well be a non-generic 1.1 .NET collection such as an array list which are collections of objects. Iterating on such a structure would attempt to assign null giving the null reference exception. Below is written in 2.0 but uses the 1.1 collection ArrayList.
ArrayList list = new ArrayList(); list.Add(DateTime.Now); list.Add(null); foreach(DateTime d in list) { MessageBox.Show(d.ToShortDateString()); }
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Since daten is not defined in could very well be a non-generic 1.1 .NET collection such as an array list which are collections of objects. Iterating on such a structure would attempt to assign null giving the null reference exception. Below is written in 2.0 but uses the 1.1 collection ArrayList.
ArrayList list = new ArrayList(); list.Add(DateTime.Now); list.Add(null); foreach(DateTime d in list) { MessageBox.Show(d.ToShortDateString()); }
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No, it couldn't. If the daten collection would contain something other than DateTime values, the error would appear when the value is put in the d variable, not when the d variable is later used.
--- single minded; short sighted; long gone;
Perhaps but when a question is posed so vague as to say where is my null reference exception i think any little bit of help will help. Now you are correct in that when I said d.Month I was wrong. Sometimes I say the stupidest things. Of course, that could also fall into the category of someone designing an OO language that doesn't fully support nulls until the third release.
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