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Question

How do you convert a nullable bool? to bool in C#?

I have tried x.Value or x.HasValue ...

Answer 1

You ultimately have to decide what the null bool will represent. If null should be false , you can do this:

bool newBool = x.HasValue ? x.Value : false;

Or:

bool newBool = x.HasValue && x.Value;

Or:

bool newBool = x ?? false;

Answer 2

You can use the null-coalescing operator : x ?? something x ?? something , where something is a boolean value that you want to use if x is null .

Example:

bool? myBool = null;
bool newBool = myBool ?? false;

newBool will be false.

Answer 3

You can use Nullable{T} GetValueOrDefault() method. This will return false if null.

 bool? nullableBool = null;

 bool actualBool = nullableBool.GetValueOrDefault();

Answer 4

The easiest way is to use the null coalescing operator: ??

bool? x = ...;
if (x ?? true) { 

}

The ?? with nullable values works by examining the provided nullable expression. If the nullable expression has a value the it's value will be used else it will use the expression on the right of ??

Answer 5

If you're going to use the bool? in an if statement, I find the easiest thing to do is to compare against either true or false .

bool? b = ...;

if (b == true) { Debug.WriteLine("true"; }
if (b == false) { Debug.WriteLine("false"; }
if (b != true) { Debug.WriteLine("false or null"; }
if (b != false) { Debug.WriteLine("true or null"; }

Of course, you can also compare against null as well.

bool? b = ...;

if (b == null) { Debug.WriteLine("null"; }
if (b != null) { Debug.WriteLine("true or false"; }
if (b.HasValue) { Debug.WriteLine("true or false"; }
//HasValue and != null will ALWAYS return the same value, so use whatever you like.

If you're going to convert it to a bool to pass on to other parts of the application, then the Null Coalesce operator is what you want.

bool? b = ...;
bool b2 = b ?? true; // null becomes true
b2 = b ?? false; // null becomes false

If you've already checked for null, and you just want the value, then access the Value property.

bool? b = ...;
if(b == null)
    throw new ArgumentNullException();
else
    SomeFunc(b.Value);

Answer 6

bool? a = null;
bool b = Convert.toBoolean(a); 

Answer 7

This answer is for the use case when you simply want to test the bool? in a condition. It can also be used to get a normal bool . It is an alternative I personnaly find easier to read than the coalescing operator ?? .

If you want to test a condition, you can use this

bool? nullableBool = someFunction();
if(nullableBool == true)
{
    //Do stuff
}

The above if will be true only if the bool? is true.

You can also use this to assign a regular bool from a bool?

bool? nullableBool = someFunction();
bool regularBool = nullableBool == true;

witch is the same as

bool? nullableBool = someFunction();
bool regularBool = nullableBool ?? false;

Answer 8

Something like:

if (bn.HasValue)
{
  b = bn.Value
}

Answer 9

The complete way would be:

bool b1;
bool? b2 = ???;
if (b2.HasValue)
   b1 = b2.Value;

Or you can test for specific values using

bool b3 = (b2 == true); // b2 is true, not false or null

Answer 10

This is an interesting variation on the theme. At first and second glances you would assume the true branch is taken. Not so!

bool? flag = null;
if (!flag ?? true)
{
    // false branch
}
else
{
    // true branch
}

The way to get what you want is to do this:

if (!(flag ?? true))
{
    // false branch
}
else
{
    // true branch
}

Answer 11

System.Convert对我很好。

using System; ... Bool fixed = Convert.ToBoolean(NullableBool);