The “Object reference not set to an instance of an object” is a very famous error in C# that appears when you get a NullReferenceException. This occurs when you try to access a property or method of an object that points to a null value. They can be fixed using Null conditional operators and handled using try-catch blocks.
In this post, we will learn more about the error and the ways to fix it.
What is “NullReferenceException: Object reference not set to an instance of an object” error?
As mentioned earlier, the NullReferenceException indicates that your code is trying to work with an object that has a null value as its reference. This means that the reference object has not been initialized.
This is a runtime exception that can be caught using a try-catch block.
Example code
try { string a = null; a.ToString(); } catch (NullReferenceException e) { //Code to do something with e }How to fix this error?
You can fix this error by using the following methods:
- Using Null conditional operators
- Using the Null Coalescing operator
- Using nullable datatypes in C#
1) Using Null conditional operators
This method is easier than using an if-else condition to check whether the variable value is null. Look at this example,
int? length = customers?.Length; // this will return null if customers is null, instead of throwing the exception2) Using the Null Coalescing operator
This operator looks like “??” and provides a default value to variables that have a null value. It is compatible with all nullable datatypes.
Example
int length = customers?.Length ?? 0; // 0 is provided by default if customers is null3) Using nullable datatypes in C#
All reference types in C# can have a null value. But some data types such as int and Boolean cannot take null values unless they are explicitly defined. This is done by using Nullable data types.
For example,
static int Add(string roll_numbers) { return roll_numbers.Split(","); // This code might throw a NullReferenceException as roll_numbers variable can be null }Correct code
The best way to avoid the "NullReferenceException: Object reference not set to an instance of an object”error is to check the values of all variables while coding. You can also use a simple if-else statement to check for null values, such as if (numbers!=null) to avoid this exception.
Hello and thank for your product and help:
Xamarin Form: 5.0.0.2125
Syncfution: 19.3.0.45
Platform: Android
1==> I have sfpopup1 defined in mypage.xaml
2==> this sfpopup1 call a custom view its datatemplate :
<sfpopup:PopupView.ContentTemplate>
<DataTemplate>
<ContentView>
<ContentView.Content>
<customViews:mycustomView/>
</ContentView.Content>
</ContentView>
</DataTemplate>
</sfpopup:PopupView.ContentTemplate>
3==> in mycustomView i have a definition of sfpopup2.
PB scenario :
when i click for the first time on sfpopup1 it show me the data and i can click to show the second popup2 with success.
But when i close the popup2 and then i close the popup1, then i click to open the popup1 again, for the second time, i got this error :
$exception {System.NullReferenceException: Object reference not set to an instance of an object.
at Syncfusion.XForms.Android.PopupLayout.PopupLayoutDependencyService.Show (System.Object nativeObject, Syncfusion.XForms.PopupLayout.SfPopupLayout formsPopup) [0x00017] in <2a371ae052bd4549be9649e4f0ade4d0>:0
at Syncfusion.XForms.PopupLayout.SfPopupLayout.Show (System.Boolean isFullScreen) [0x00018] in <452eb09ad7204bdc8957931a3d022370>:0
at Syncfusion.XForms.PopupLayout.SfPopupLayout.OnIsOpenChanged (Xamarin.Forms.BindableObject bindable, System.Object oldValue, System.Object newValue) [0x0007f] in <452eb09ad7204bdc8957931a3d022370>:0
at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty property, Xamarin.Forms.BindableObject+BindablePropertyContext context, System.Object value, System.Boolean currentlyApplying, Xamarin.Forms.Internals.SetValueFlags attributes, System.Boolean silent) [0x00120] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:512
at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, Xamarin.Forms.Internals.SetValueFlags attributes, Xamarin.Forms.BindableObject+SetValuePrivateFlags privateAttributes) [0x00173] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:446
at Xamarin.Forms.BindingExpression.ApplyCore (System.Object sourceObject, Xamarin.Forms.BindableObject target, Xamarin.Forms.BindableProperty property, System.Boolean fromTarget) [0x00226] in D:\a\1\s\Xamarin.Forms.Core\BindingExpression.cs:160
at Xamarin.Forms.BindingExpression.Apply (System.Boolean fromTarget) [0x0003e] in D:\a\1\s\Xamarin.Forms.Core\BindingExpression.cs:56
at Xamarin.Forms.BindingExpression+BindingExpressionPart.<PropertyChanged>b__49_0 () [0x00000] in D:\a\1\s\Xamarin.Forms.Core\BindingExpression.cs:762
at Xamarin.Forms.BindingExpression+BindingExpressionPart.PropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs args) [0x000cb] in D:\a\1\s\Xamarin.Forms.Core\BindingExpression.cs:773
at Xamarin.Forms.BindingExpression+WeakPropertyChangedProxy.OnPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs e) [0x00012] in D:\a\1\s\Xamarin.Forms.Core\BindingExpression.cs:666
NB :
if i change the call of popup2 by navigation to a new page from the popup1, it works fine.