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I know that Func<t,tresult> is a delegate that takes T as a parameter and returns TResult as an output but I do not know what the following means.
Expression<Func<T, TResult>>
Can someone please explain what the above syntax means and how it is used.
modified 27-Dec-16 17:50pm.
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Hi, thanks for replying. Your link does not help me understand what an Expression is in C# or how to use it.
I came across a method the other day and I was trying to find out what the syntax is trying do. I've been looking at tutorials on Expression on Youtube and Google but it didn't really help.
The following is the method I mentioned but I don't really know what it is supposed to do.
public IEnumerable<T> Find(Expression<Func<T, bool>> predicate)
{
return Context.Set<T>().Where(predicate);
}
modified 28-Dec-16 10:31am.
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In what you have posted here it allows you to pass a lambda statement as the argument. For example
MyClass.Find(p=> p.id == 12);
or
string[] toInclude = new string[] { "Hi", "Why", "Bye"};
MyClass.Find(p=> toInclude(p) == true);
Every day, thousands of innocent plants are killed by vegetarians.
Help end the violence EAT BACON
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Expression<Func<T, TResult>> represents a strongly-typed expression tree of a lambda or function. Expression trees represent expressions like a < b stored in a tree structure. So what are they used for? Well, that's open to your imagination honestly. A common scenario is if you want to modify a code expression based on some currently unknown or later business logic. Since an expression tree is a data representation of a code expression you're free to modify it before calling Compile() and executing it. This is essential for LINQ-to-SQL which transforms expressions like from a in db.table select a into an expression tree which is then transformed into the necessary SQL for the actual DB call. Expression trees are also heavily used in the Dynamic Language Run-time.
As far as the specific example in your other post:
public IEnumerable<T> Find(Expression<Func<T, bool>> predicate)
{
return Context.Set<T>().Where(predicate);
}
Context is most likely a DbContext object. Set<T>() returns a DbSet<T> of all entities of the type given to Set. Then Where is called to filter the result based on the predicate expression which, instead of just being a lambda, is stored as an expression tree - I'm guessing because of some other logic elsewhere in the application otherwise this seems a little over-the-top.
EDIT: Forgot to add how to use them. In LINQ you treat it like any other function. Outside of LINQ you call Compile() to create the Func delegate. To create them is as simple as assigning a lambda in simple cases. For example, Expression<Func<int,int>> incrementTree = a => a + 1;. In more complex cases, you may need to explicitly use the expression tree API which you can find links to in the MSDN guide below.
Further reading:
Expression Tree Basics
Expression Trees - MSDN
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Cela est normal avec windows10 pour une application universelle car c'est le système d'exploitation qui gère la permission de l'utilisateur OK bien !!! Mais mon application est automatiquement compatible Windows 8.x lors de la soumission au store et il échoue puisque avec 8.x c'est le programmeur qui gère l'autorisation avec le code:
Var accessStatus = await Geolocator.RequestAccessAsync (); demande d'accès
Switch (accessStatus) // test d'accèsStatus
Dans visual studio 2015 aucune définition dans geolocator pour requestaccessasync (), (seulement "égal" et "égal de référence") quelqu'un saurait comment contourner ce problème je cherche depuis une semaine.
je doit donc tester si ce n'est pas windows10 (ça d'accord) et dans ce cas demander l'autorisation d'accéder à la geolocalisation à l'utilisateur qui devrait se faire avec le code çi dessus mais c'est impossible je suis donc dans une belle impasse.
je vous souhaite à tous de bonnes fêtes.
bonnes fêtes à tous
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This is an English language site, and we can only answer questions in English.
Please try using Google Translate:
This is normal with windows10 for a universal application because it is the operating system that manages the permission of the user OK well !!! But my application is automatically compatible Windows 8.x when submitting to the store and it fails since with 8.x it is the programmer who manages the authorization with the code:
Var accessStatus = await Geolocator.RequestAccessAsync (); Request for access
Switch (accessStatus) // access testStatus
In Visual Studio 2015 no definition in geolocator for requestaccessasync (), (only "equal" and "reference equal") someone would know how to get around this problem I've been looking for a week.
I have to test if it is not windows10 (that agrees) and in this case ask permission to access the geolocation to the user who should be done with the code above but it is impossible I I am therefore in a beautiful dead end.
I wish you all a happy holiday.
Happy Holidays to all
But it doesn't make a lot of sense to me even translated - it looks like an attempt at an answer in parts, but to what I am not sure...
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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La langue de ce site est l'Anglais, donc les questions doivent être en Anglais.
Je ne vois pas bien quelle est la question.
Patrice
“Everything should be made as simple as possible, but no simpler.” Albert Einstein
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I saw these tutorials and i got interest to make my own remote Desktop viewer, hence i wanted to ask how can i enable mouse etc inside the program
https:
https:
How do i go about it?
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You already received some suggestions in your QA question at Creating remote desktop in WINAPI C++[^]. The authors of the youtube videos are the only people who can answer questions on what they suggest.
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private void exprtbtn_Click(object sender, EventArgs e)
{
try
{
if ((this.dataGridView1.Rows.Count == 0))
{
MessageBox.Show("Please select Vouchers");
}
else
{
SqlConnection con = null;
SqlConnection con2 = null;
connClass cs = new connClass();
con = new SqlConnection(cs.distiConn1);
con2 = new SqlConnection(cs.sourceConn2);
ArrayList a = new ArrayList();
DataTable DT = new DataTable();
SqlCommand cmd = new SqlCommand();
SqlTransaction trans = default(SqlTransaction);
con.Open();
trans = con.BeginTransaction();
cmd.Connection = con;
cmd.Transaction = trans;
SqlCommand cmdLive = new SqlCommand();
cmdLive.Connection = con2;
SqlDataAdapter DR = default(SqlDataAdapter);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((((bool)(row.Cells[this.invoiceNO.Index].Value)) == true))
{
a.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
int C = a.Count;
string str = "(";
int i = 0;
while (i < C - 1)
{
str += "'" + a[i] + "',";
i = i + 1;
}
str += "'" + a[C - 1] + "')";
cmdLive.CommandText = ("Select * from InvDailyHF where compno=1 and VouYear="
+ (this.yercombox.Text + (" and VouType="
+ (this.vochcombox.Text + (" and VouNo in " + str)))));
DR = new SqlDataAdapter(cmdLive);
DR.Fill(DT);
int CC = DT.Columns.Count;
string strn = "(";
int i1 = 0;
foreach (DataRow R in DT.Rows)
{
while (i1 < CC - 1)
{
strn += "'" + R[i1] + "',";
i1 = i1 + 1;
}
strn += "'" + R[CC - 1] + "')";
cmd.CommandText = ("Insert InvDailyHF values" + strn);
cmd.ExecuteNonQuery();
}
}
SqlConnection con3 = null;
SqlConnection con4 = null;
connClass csu = new connClass();
con3 = new SqlConnection(csu.sourceConn2);
con4 = new SqlConnection(csu.distiConn2);
ArrayList aH = new ArrayList();
DataTable DTH = new DataTable();
SqlCommand cmd1 = new SqlCommand();
SqlCommand cmdLiveh = new SqlCommand();
cmdLiveh.Connection = con3;
cmd1.Connection = con4;
SqlDataAdapter DAH = default(SqlDataAdapter);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
aH.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
int BB = aH.Count;
string strn1 = "(";
int i2 = 0;
while (i2 < BB - 1)
{
strn1 += "'" + aH[i2] + "',";
i2 = i2 + 1;
}
strn1 += "'" + aH[BB - 1] + "')";
cmdLiveh.CommandText = ("Select * from InvDailyDF where compno=1 and VouYear="
+ (this.yercombox.Text + (" and VouType="
+ (this.vochcombox.Text + (" and VouNo in " + strn1)))));
DAH = new SqlDataAdapter(cmdLiveh);
DAH.Fill(DTH);
int BB1 = DTH.Columns.Count;
string strn2 = "(";
int i3 = 0;
foreach (DataRow R in DTH.Rows)
{
while (i3 < BB1 - 1)
{
strn2 += "'" + R[i3] + "',";
i3 = i3 + 1;
}
strn2 += "'" + R[BB1 - 1] + "')";
}
cmd1.CommandText = ("Insert InvDailyDF values" + strn2);
cmd1.ExecuteNonQuery();
strn2 = "(";
i3 = 0;
ArrayList transData = new ArrayList();
DataTable transDT = new DataTable();
SqlCommand cmdTrans = new SqlCommand();
SqlDataAdapter transDR = new SqlDataAdapter();
int transCount;
int transCounter;
int DTcounter;
int iString;
string transDA = "(";
if (vochcombox.Text == "9")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn2);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=4 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "2")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=6 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "3")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=8 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "10")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=9 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "4")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=13 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "13")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=14 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
else if (this.vochcombox.Text == "6")
{
cmdTrans.Connection = new SqlConnection(cs.sourceConn1);
foreach (DataGridViewRow row in this.dataGridView1.Rows)
{
if ((bool)row.Cells[this.invoiceNO.Index].Value == true)
{
transData.Add(row.Cells[this.invoiceNO.Index].Value);
}
}
transCount = transData.Count;
transDA = "(";
transCounter = 0;
while ((transCounter
< (transCount - 1)))
{
transDA = (transDA + ("\'"
+ (transData[transCounter] + ("\',"))));
transCounter = (transCounter + 1);
}
transDA = (transDA + ("\'"
+ (transData[(transCount - 1)] + "\')")));
cmdTrans.CommandText = ("Select * from glvodmf where vod_comp=1 and vod_year="
+ (this.yercombox.Text + (" and vod_type=61 and vod_num in " + transDA)));
transDR = new SqlDataAdapter(cmdTrans);
transDR.Fill(transDT);
DTcounter = transDT.Columns.Count;
transDA = "(";
iString = 0;
foreach (DataRow R in transDT.Rows)
{
while (iString
< (DTcounter - 1))
{
transDA = transDA + ("\'"
+ (R[iString] + "\',)"));
iString = (iString + 1);
}
transDA = (transDA + ("\'"
+ (R[(DTcounter - 1)] + "\')")));
cmdTrans.CommandText = ("Insert glvodmf values" + transDA);
cmdTrans.ExecuteNonQuery();
transDA = "(";
iString = 0;
}
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
modified 26-Dec-16 2:59am.
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Specified cast is not valid.
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So the Value of that cell cannot be cast to a bool type. You need to investigate why.
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We can't tell without knowing what the error is - but it's most likely that this.invoiceNO.Index is trying to reference a cell that doesn't exist - it would be very unusual to have a table which held all invoices as vertical columns: normally it would be the row that is indexed to supply all the information for a single invoice, not the column:
Columns -> Invoice No Customer Date ItemsCost VAT TotalInvoiced
Rows 1001 Smiths 2016/12/14 102.37 20.47 122.84
| 1002 Johnson 2016/12/15 1247.99 ...
V 1003 Smiths 2016/12/15 742.65 ...
...
So use the debugger and see what value you have, and check the actual column data against that.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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this is debugger error(Specified cast is not valid.)
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So use the debugger to look at the value of that cell and find out what type of data it contains. When you know that, you can start looking at why it isn't a boolean value.
We can't do that for you: we can't run your code, and don't have your data which fills the table if we could!
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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did you have a time to take a look via teamviewr
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Are you clinically insane?
You would allow total strangers you never met to remotely control your PC?
Have you any idea what some of them might do?
Have you ever heard of ransomware?
If you have that enabled, disable it immediately!
Use the debugger.
Look at the cell content. It should tell you a lot.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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no i'm not clinically insane.... but we are in a community to help each author.and i'm stacked.
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We are in a community to help each other, but you have no idea who people are, and what they are going to do. This is the real world, and leaving your machine open for total strangers to access and do whatever they want - and if you give them access to VS that's exactly what they can do - is not "asking for trouble" it's inviting it indoors, giving it a beer, and telling it where you keep your credit cards! 
Be realistic and honest: you know how to use the debugger, don't you? (If you don't, then say so and we'll try to get you started. But not telling us relevant information is just wasting your own time, as well as ours)
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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many thanks for your advice and your time.
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You're welcome!
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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