"Cannot implicitly convert type 'void' to 'system.collections.generic.list<helptoearn.models.allpayouts>" while updating list

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I have to update list values with new values daily. the new value is listvalue+newvalue

What I have tried:

allPayouts = (from p in allPayouts where p.UserID == Paid.UserID select p).ToList().ForEach((p) =>
{
p.LeftPoint = payoutList.Select(u => Convert.ToDouble(u.LeftPoint)).FirstOrDefault();
p.RightPoint += payoutList.Select(u => Convert.ToDouble(u.RightPoint)).FirstOrDefault();
p.BinaryIncome = payoutList.Select(u => u.BinaryIncome).FirstOrDefault();

});

Posted 14-May-20 22:41pm

Member 13160027

Updated 15-May-20 4:20am

v2

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Richard MacCutchan 15-May-20 4:42am

It just means that your LINQ code is not returning any items. Use your debugger to find out why.

2 solutions

Solution 1

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

private int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Posted 14-May-20 23:19pm

OriginalGriff

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Richard Deeming · Accepted Answer · 2020-05-15T04:21:00

.ToList returns a List<T>[^].

The list's ForEach method[^] executes a specified action for each item in the list. It does not return anything.

Therefore, you cannot assign the return value (which doesn't exist) of that method to your variable.

Try:

C#

allPayouts = (from p in allPayouts where p.UserID == Paid.UserID select p).ToList();
allPayouts.ForEach(p =>
{
    p.LeftPoint = payoutList.Select(u => Convert.ToDouble(u.LeftPoint)).FirstOrDefault();
    p.RightPoint += payoutList.Select(u => Convert.ToDouble(u.RightPoint)).FirstOrDefault();
    p.BinaryIncome = payoutList.Select(u => u.BinaryIncome).FirstOrDefault();
});

Or, more simply:

C#

allPayouts = (from p in allPayouts where p.UserID == Paid.UserID select p).ToList();
foreach (var p in allPayouts)
{
    p.LeftPoint = payoutList.Select(u => Convert.ToDouble(u.LeftPoint)).FirstOrDefault();
    p.RightPoint += payoutList.Select(u => Convert.ToDouble(u.RightPoint)).FirstOrDefault();
    p.BinaryIncome = payoutList.Select(u => u.BinaryIncome).FirstOrDefault();
}

NB: The values you're assigning within the list don't seem to change. You can probably move those calculations outside of the loop:

C#

allPayouts = (from p in allPayouts where p.UserID == Paid.UserID select p).ToList();

var firstPayout = payoutList.FirstOrDefault();
double leftPoint = firstPayout == null ? default : Convert.ToDouble(firstPayout.LeftPoint);
double rightPoint = firstPayout == null ? default : Convert.ToDouble(firstPayout.RightPoint);
var binaryIncome = firstPayout == null ? default : firstPayout.BinaryIncome;

foreach (var p in allPayouts)
{
    p.LeftPoint = leftPoint;
    p.RightPoint += rightPoint;
    p.BinaryIncome = binaryIncome;
}