类中的哈希表集合 - 帮助! [英] hashtable collection in a class--help!
问题描述
我是C#的新手,并且使用包含哈希表
集合的类来提供树视图。我的问题是我无法从哈希表中提取
数据!
这是我的代码:
if(myItem.DataFields.Count!= 0)
foreach(myItem.DataFields.Values中的字符串名称){
treeView1.SelectedNode。 Nodes.Add(name); //这行错误
}
myItem是我班级的一个实例,DataFields是哈希表,
你我可以看到我正在尝试访问包含值的列。我在运行时得到了''
'''System.NullReferenceException''。
有人可以帮忙吗?我接近这整件事了吗?
谢谢,
Brian
< blockquote> Brian,
Hashtable用于通过密钥访问成员。我之前从未使用过Hashtable
;如果你只是想将一个对象列表存储到
retreive,那么ArrayList要轻得多。
话虽如此 - 假设那些字符串真的是字符串在此之前你已经存入了
Hashtable - 沿着
myItem.DataFields.Add(somekey,Foo)的行 - 然后你应该能够像他们一样转发
:
foreach(myEtem.DataFields中的DictionaryEntry de){
treeView1.SelectedNode .Nodes.Add((string)de.Value);
}
你可能会看到它是否有效......
>
--BOB
" Brian" <峰; br ********* @ ky.gov>在消息中写道
news:63 ************************** @ posting.google.c om ...
我是C#的新手,并且使用包含哈希表
集合的类来提供树视图。我的问题是我无法从哈希表中提取
数据!
这是我的代码:
if(myItem.DataFields) .Count!= 0)
foreach(myItem.DataFields.Values中的字符串名称){
treeView1.SelectedNode.Nodes.Add(name); //这行错误
}
myItem是我的类的一个实例,DataFields是哈希表,你可以看到我正在尝试访问包含的列值。我在运行时得到''System.NullReferenceException''。
有人可以帮忙吗?我接近这一切都错了吗?
谢谢,
Brian
Brian< br **** *****@ky.gov>写道:我是C#的新手,并且使用包含哈希表
集合的类来提供树视图。我的问题是我无法从哈希表中提取
数据!
这是我的代码:
if(myItem.DataFields) .Count!= 0)
foreach(myItem.DataFields.Values中的字符串名称){
treeView1.SelectedNode.Nodes.Add(name); //这行错误
}
myItem是我的类的一个实例,DataFields是哈希表,你可以看到我正在尝试访问包含的列值。我在运行时得到''System.NullReferenceException''。
有人可以帮忙吗?我接近这整件事是错误的吗?
事实上你有一个NullReference异常表明你已经可能了b $ b b没有选择的节点。
-
Jon Skeet - < sk *** @ pobox.com>
http://www.pobox.com/~skeet
如果回复对于小组,请不要给我发邮件
感谢您的回复,鲍勃。我实际上是使用哈希表来
存储键/值对。我试图将值添加到我的
树视图中。
您在下面给我的代码会产生一条错误消息:
>
SystemNullReferenceException
附加信息:对象引用未设置为对象的实例
任何想法是怎么回事?
--------------
Brian,
Hashtable用于访问会员通过钥匙。我以前从未用这种方式使用过
Hashtable
;如果你只是想将一个对象列表存储到
retreive,那么ArrayList要轻得多。
话虽如此 - 假设那些字符串真的是字符串在此之前你已经存储了
Hashtable -
myItem.DataFields.Add(somekey,") ; Foo) - 然后你应该能够
retreive
他们是这样的:
foreach(DictionaryEntry de in myItem.DataFields){
treeView1.SelectedNode.Nodes.Add((string)de.Value);
}
你可能会看到它是否有效...
--BOB
" Brian" <峰; br ********* @ ky.gov>在消息中写道
news:63 ************************** @ posting.google.c om ...我是C#的新手,并且使用包含哈希表
集合的类来提供树视图。我的问题是我无法从哈希表中提取
数据!
这是我的代码:
if(myItem.DataFields) .Count!= 0)
foreach(myItem.DataFields.Values中的字符串名称){
treeView1.SelectedNode.Nodes.Add(name); //这行错误
}
myItem是我的类的一个实例,DataFields是哈希表,你可以看到我正在尝试访问包含的列值。我在运行时得到''System.NullReferenceException''。
有人可以帮忙吗?我接近这整件事了吗?
谢谢,
Brian
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I''m reasonably new to C#, and using a class containing a hashtable
collection to feed a treeview. My problem is that I can''t pull the
data from the hashtable!
Here''s the code I have:
if (myItem.DataFields.Count != 0)
foreach (string name in myItem.DataFields.Values) {
treeView1.SelectedNode.Nodes.Add (name); // Error on this line
}
myItem is an instance of my class, DataFields is the hashtable, and
you can see I''m trying to access the column containing values. I get
a ''System.NullReferenceException'' at runtime.
Can someone help? Am I approaching this whole thing wrong?
Thanks,
Brian
Brian,
A Hashtable is for accessing members via a key. I''ve never used a Hashtable
in this way before; if you simply want to store a list of objects to
retreive, an ArrayList is much more lightweight.
Having said that -- assuming those really are strings you''ve stored into the
Hashtable prior to this -- along the lines of
myItem.DataFields.Add(somekey,"Foo") -- then you should be able to retreive
them like so:
foreach (DictionaryEntry de in myItem.DataFields) {
treeView1.SelectedNode.Nodes.Add((string)de.Value) ;
}
You might see if that works ...
--Bob
"Brian" <br*********@ky.gov> wrote in message
news:63**************************@posting.google.c om...I''m reasonably new to C#, and using a class containing a hashtable
collection to feed a treeview. My problem is that I can''t pull the
data from the hashtable!
Here''s the code I have:
if (myItem.DataFields.Count != 0)
foreach (string name in myItem.DataFields.Values) {
treeView1.SelectedNode.Nodes.Add (name); // Error on this line
}
myItem is an instance of my class, DataFields is the hashtable, and
you can see I''m trying to access the column containing values. I get
a ''System.NullReferenceException'' at runtime.
Can someone help? Am I approaching this whole thing wrong?
Thanks,
Brian
Brian <br*********@ky.gov> wrote:I''m reasonably new to C#, and using a class containing a hashtable
collection to feed a treeview. My problem is that I can''t pull the
data from the hashtable!
Here''s the code I have:
if (myItem.DataFields.Count != 0)
foreach (string name in myItem.DataFields.Values) {
treeView1.SelectedNode.Nodes.Add (name); // Error on this line
}
myItem is an instance of my class, DataFields is the hashtable, and
you can see I''m trying to access the column containing values. I get
a ''System.NullReferenceException'' at runtime.
Can someone help? Am I approaching this whole thing wrong?
The fact that you''ve got a NullReference exception suggests that you''ve
probably not got a SelectedNode.
--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Thanks for the response, Bob. I actually am using the hash table to
store key/value pairs. I was trying to add just the values to my
treeview.
The code you gave me below creates an error message:
SystemNullReferenceException
Additional Info: Object reference not set to an instance of an object
Any ideas what is going on?
--------------
Brian,
A Hashtable is for accessing members via a key. I''ve never used a
Hashtable
in this way before; if you simply want to store a list of objects to
retreive, an ArrayList is much more lightweight.
Having said that -- assuming those really are strings you''ve stored into
the
Hashtable prior to this -- along the lines of
myItem.DataFields.Add(somekey,"Foo") -- then you should be able to
retreive
them like so:
foreach (DictionaryEntry de in myItem.DataFields) {
treeView1.SelectedNode.Nodes.Add((string)de.Value) ;
}
You might see if that works ...
--Bob
"Brian" <br*********@ky.gov> wrote in message
news:63**************************@posting.google.c om...I''m reasonably new to C#, and using a class containing a hashtable
collection to feed a treeview. My problem is that I can''t pull the
data from the hashtable!
Here''s the code I have:
if (myItem.DataFields.Count != 0)
foreach (string name in myItem.DataFields.Values) {
treeView1.SelectedNode.Nodes.Add (name); // Error on this line
}
myItem is an instance of my class, DataFields is the hashtable, and
you can see I''m trying to access the column containing values. I get
a ''System.NullReferenceException'' at runtime.
Can someone help? Am I approaching this whole thing wrong?
Thanks,
Brian
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