Cannot implicitly convert type 'object' to 'bool'

Tichaona J

I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<

Luc Pattyn

== :)

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Lost User

Instead of coding:

if (btnPause.Content == "Pause")

try writing it this way round

if ("Pause" == btnPause.Content)

then when you inadvertently miss one of the = signs the compiler will give you a much more useful message.

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Lost User

Richard MacCutchan wrote:

the compiler will give you a much more useful message.

I don't know about that, you'd get "The left-hand side of an assignment must be a variable, property or indexer", which is true of course but it tells you to fix the wrong thing, it's saying that you should change the LHS into a variable. It's also saying that it's an assignment, but that just adds to the confusion because "there is no assignment, so the error makes no sense". OTOH, the "Cannot implicitly convert [type] to bool" is entirely clear, and since it's pointing to an expression in an if it tells you "you stuck something into an if that is not a bool" which is exactly what the problem is. Or maybe I'm just used to that kind of error.. edit: I did not vote "bad answer" by the way, so don't get mad at me please :)

modified on Saturday, August 7, 2010 10:34 AM

Luc Pattyn · modified on Saturday, August 7, 2010 10:34 AM

it really should say

if() expects a boolean and "btnPause.Content" isn't a boolean nor convertible to one

and it could add

there is an assignment in your expression; did you intend to test for equality? if so use ==

Why can't error messages be very specific, after all the parser is specific when it checks things.

harold aptroot wrote:

I did not vote "bad answer"

Neither did I, although I didn't like it much; the user should not change his habits just because the compiler lacks proper error reporting. The suggestion may be OK for C/C++, but doesn't help much for C# code. :)

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modified on Saturday, August 7, 2010 10:51 AM

Keith Barrow

I don't like this way of working personally, I think the semantics are less clear and it always feels like cutting the suit to match the cloth to me. I vaguely remember it was a good idea to use the 2nd form in C++, the compiler wouldn't throw an error otherwise, and would happily set btnPause.Content to "Pause" I haven't voted (and won't :-) ) vote on your response - I don't think there is anything wrong with what you said, it is just a different opinion about how to work.

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Lost User · modified on Saturday, August 7, 2010 10:51 AM

:(( suitably chastised ...

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Luc Pattyn

:beer:

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Lost User

I have to say I tend to use the alternate form somewhat less these days, but it was offered to me years ago as a good way of catching such mistakes, especially in the days before C++ when I was writing pure C. And as for the down voting, well frankly my dear ... I just wish these jerks would have the guts to add a reasoned and useful argument as the rest of you have done.

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Orjan Westin

There's a difference between

if (btnPause.Content = "Pause")

and

if (btnPause.Content == "Pause")

You aren't comparing with btnPause.Content, but assigning to it. The assignment operator returns the assigned object, so in effect your code is like this:

btnPause.Content = "Pause";
if (btnPause)

It's a classic typo-bug, and the safest way of avoiding it is to make a habit of putting the constant (if you have one) to the left:

if ("Pause" = btnPause.Content)

This would give a compiler error along the lines of "Cannot assign to constant", which is more helpful.

Lost User

I already suggested this above; you may want to read Harold, Luc and Keith's comments in response. Also note that someone around here really hates this idea and is downvoting us for suggesting it. I've given you a 5 to compensate. ;)

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Orjan Westin

Yes, I saw that once I'd replied. It was the changed subject line that threw me off. Sorry, I'm new in the neighbourhood. :)

PIEBALDconsult

I used to work in a shop (doing just plain C) that had that specified in the coding standards. It made no sense to me, but I went along. One day I was talking with "the guru" (who probably wrote the standard) and he agreed that it was pointless so he didn't enforce it. The basic problem is that it only works when comparing an Lvalue and an Rvalue; many times that is not the case, so you need to think about what you are doing and recognize the situation. And if you can do that, then chances are you won't make that mistake anyway. When it comes right down to it; anyone who is prone to that kind of mistake is also unlikely to remember the rule. By the way... HP C V7.3-009 on OpenVMS Alpha V8.3 says:

JB> cc aa.c /warn=(enable=(check),verbose)

if ( result = 5 )

....^
%CC-I-CONTROLASSIGN, In this statement, the assignment expression "result=5" is used as the controlling expression of an if, while o
r for statement.
at line number 13 in file MY$ROOT:[000000]AA.C;3
Description: A common user mistake is to accidentally use assignment operator "=" instead of the equality operator "==" in an expres
sion that controls a transfer. For example saying if (a = b) instead of if (a == b). While using the assignment operator is valid,
it is often not what was intended. When this message is enabled, the compiler will detect these cases at compile-time. This can oft
en avoid long debugging sessions needed to find the bug in the user's program.
User Action: Make sure that the assignment operator is what is expected.

if ( 5 = result )

.........^
%CC-E-NEEDLVALUE, In this statement, "5" is not an lvalue, but occurs in a context that requires one.
at line number 18 in file MY$ROOT:[000000]AA.C;3
Description: An expression that must be an lvalue was not an lvalue. For example, the operand of the address-of operator must be an
lvalue.
User Action: Modify the expression so that it is an lvalue.

Edit:

C:\>cc aa
Borland C++ 5.5 for Win32 Copyright (c) 1993, 2000 Borland
aa.c:
Warning W8060 aa.c 14: Possibly incorrect assignment in function main

C:\>\mingw\bin\gcc -Wall aa.c
aa.c: In function `main':
aa.c:14: warning: suggest parentheses around assignment used as truth value

modified on Saturday, August 7, 2010 11:40 PM

Luc Pattyn · modified on Saturday, August 7, 2010 11:40 PM

Right. I've seen some C compilers (don't recall which, I've used so many for all kinds of embedded systems) also warning about the probably mistaken assignment in an if statement. :)

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PIEBALDconsult

Personally, I'd prefer to hide the Pause button and show the resume button rather than repurpose the one button and do string compares.

Lost User

Cool Cow Orjan wrote:

Sorry, I'm new in the neighbourhood.

No problem, we all make mistakes from time to time. And welcome to CodeProject, judging by some of your posts I have seen I am sure your contributions will have a positive impact for many people. :thumbsup:

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Lost User · modified on Saturday, August 7, 2010 11:40 PM

I thought I had seen something like that in my days as a UNIX programmmer, it must have been gcc and possibly Sun' own C/C++ compiler.

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cor2879

Personally when performing value comparisons with strings (and many other types) I find I am far less prone to syntax errors if I make myself use the "Equals" method. With strings in particular, it is a good practice to use the static method

String.Equals(string a, string b)

as this eliminates the possibility of a null reference exception. With this in mind, the boolean in your if statement would look like this:

if (String.Equals(btnPause.Content, "Pause"))

"We are men of action; lies do not become us."

michaelbierly

you are trying to assign "Pause" to btnPause.content (=) you need the equality comparison operator (==) I dont have a lot of context to what you are doing, but you might want to try refering to sender rather than btnPause in the code.

tom1443

Ah, bitten by the old "==" typo. Don't feel bad it was my first coding mistake in C 25 years ago. I still occasionally make that error but it usually takes me a whole lot less time to find it.