Hi guys I need a little advice. I trying to made an android app using Xamarin so C.
I made two layouts and in each one of them I made tow buttons to navigate between them. I tried like this:.
But every time when I start the app I get this errror: System. NullReferenceException has been thrown. Object reference not set to an instance of an object.
Any advice or better idea? You are setting Main as the layout for your activity and then in the following lines of code you are asking to find a button named Back at runtime which is not part of this layout.
This means the following line will return null:. Clickyou will definitely get a System. Create two different activities Main1 and Main2. In Main1 you do:.
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Since it just happened to me and almost drove me up the wall, here is yet another way FindViewById can return null and how to fix it.
Probably not a mistake a more experienced Android developer is likely to make, but still, it might prevent some frustration for someone like me in the future. My control was in the correct view not a fragmentthe ID was assigned correctly, everything used to work just a couple of days ago when I last worked on the project.
After building the project, the very first FindViewById call in OnCreate of my main view suddenly returned null when run on a physical device. It turns out I had just run some updates through the Android SDK Manager, which introduced a new Android Version in this case Android 7 to my system, and my device simply did not have that version installed yet.
TL;DR Check that the version of Android you are compiling against is in fact supported by the device you are testing on. You're getting a NullReferenceException because this code:. Therefore the FindViewById method can't find it. Your intended approach to switch screens isn't supported on Android.
Which leads to a longer explanation about the Correct way to "switch screens" on Android: navigating between simple activities. Learn more. Asked 5 years, 8 months ago. Active 3 years, 4 months ago. Viewed 13k times. I tried like this: using System; using Android.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Error:- Type inference failed: Not enough information to infer parameter T. You can use Kotlin Android Extensions too for that. Check the doc here. How does it work? You can see the relevant changelog here. In Kotlin we can get the id of the view without the use of the findViewById syntax.
For example we are using the following the layout from that we will get the id of the view and perform operation. To be able to use it, you need an special import the one I write belowbut the IDE is able to auto-import it. We need to import this property to get the id of the view without the use of the findviewbyid syntax.
For more information on this topic than please refer this link :- Click here. I'd like to add that, using Ankoyou can further simplify your code like this:. Here bind generic function use to bind view. You don't even have to create an object to do things with a view. You can just use the id. For example, Kotlin. Learn more. Asked 2 years, 9 months ago. Active 2 years, 3 months ago. Viewed 32k times.
I am getting the following error when I try to find a RecycleView by id. Ravindra Kushwaha. Ravindra Kushwaha Ravindra Kushwaha 5, 8 8 gold badges 35 35 silver badges 71 71 bronze badges.
Active Oldest Votes. Kotlin Android Extensions: In your app gradle. Kevin Robatel Kevin Robatel 5, 2 2 gold badges 30 30 silver badges 49 49 bronze badges. Brilliant solution! Helped me a lot!The first presentation I witnessed made it sound quite interesting, but the minute I decided to try it out, I truly fell in love with it. One of the many things that attracted me most was how you could avoid the so dreaded NullPointerException by properly handling optional types.
Far from the perplexity I felt when I first discovered that feature in Swift five years ago, it now felt much more natural in Kotlin. Getting NullPointerExceptions is actually as simple as using a double bang. Not all variables can be nullso why should one be nullable and what does it imply? The trick we fell for as java coders is that null was such an easy default value for our variables.
If you started to implement an abstract method in your class, your IDE would stub its body with a return null. In lots of cases, non-null values can be totally valid default values. Think about primitive types: until autoboxing arrived in Java 5, most of us never bothered to wrap numbers in Objects. The takeaway here is that null is not necessarily your only choice as a default value, and you should probably think twice before resorting to it.
You could even guard certain variables against ever risking to receive a null value in case some rogue Java code tried to sneak it behind your back with a simple Elvis operator:. Based on your business logic, it might be obvious that whenever you will need to access a certain variable, that value will not be null. Until you call setContentViewcalling your variable would return null. The first that might come to mind is not necessarily the safest.
The lateinit keyword allows you to explicitly state that a variable is never null when it is read, even if it does not immediately contain a value. This implies a certain rigor on your part to make sure no scenario exists where that condition could be violated. Be a bit negligent with it and you will soon realize that NullPointerExceptions still happen in Kotlin!
Other choices include the use of custom getters or delegates. So you could simply replace that field with a dynamic calculation:.
Or use a delegate to compute that value. Especially when you realize that Kotlin developers got you covered with a clever smartcast to simplify your syntax.I am trying to display two values that are obtained from a SQL query and present the values inside the TextViews.
In my LiveBarcodeScanningActivity I tried putting the above statements inside the onCreate but it crashes right when the app launches the activity. Why am I getting the errorwhen the fetch url is ok?
I am currently facing an issue to test an object value which is inside the run method of a private inner class using MockitoHere is my structure:. I have another section below where I tried to change the text values: workflowModel?. Here is the warning message I get: java. Home Android java. IllegalStateException: [TextView] must not be null.
But when I run the app an error comes up at the dateText. Possibilities : 1 you might be using wrong id of textview 2 you may have used wrong file while inflating view. If you are using fragments: 1. Use a global variable that will hold your layout reference. To use any view of your layout which is inside your layout you can use it with root.
It's saying your dateText view itself is null not the value listItem. The same happened to me while using Fragment, I took my code from onCreateView and put it to onViewCreated method, the problem solved. I just had the same issue with my RecyclerView. It had been working for months. It also might happen on wrong context reference in xml file, usually it appears on manualy moving Activity to another package, Android studio didn't make this change automatically:.
Learn more. Asked 2 years, 4 months ago. Active 10 months ago. Viewed 18k times. Post the XML too. Let us have a look.
FindViewById always returns null
IronyStack you are correct I was inflating wrong layout. Active Oldest Votes.I try to create custom picker for android as spinner. I want to change text size for spinner items.
I created axml file with textView for spinner items and want to change it programmatically. I'm new in xamarin and android, I don't know what I'm doing wrong. This mean, you're working with layout where you set in SetContentView not with spinnerItem layout. Also you can not define object like TextView with Resource. Layout, you must define them with their unique Id for example :.
So, I am not saying you're algorithm is good while working with Spinner, but you will be able to access that text view if you update your code.
BerayBentesenthank you. You said that my alghoritm is not good. Can you tell me how to set text size for spinner items? I'd appreciate it. Spinner item has it's own layout file.
You can use properties of TextView in xml like textSize, margin etc. BerayBentesenI did it. I created axml file with layot. I used it for creating ArrrayAdapter. But I need change textSize for spinner item programmatically.
What is Xamarin. November edited November in Xamarin. OnElementChanged e ; if e. Context ; spinner. SetTextSize global::Android. Context, Resource. Tagged: xamarin. Best Answer. November Accepted Answer. Inflate Resource. YourTextView ; So, I am not saying you're algorithm is good while working with Spinner, but you will be able to access that text view if you update your code.
Hence if I try to setonClickListener it fails the whole Activity. The button code should be moved to the PlaceholderFragment class. Like so. How should the activity find it in the content view?
The layout that contains the button is displayed by the Fragment, so you have to get the Button there, in the Fragment. Learn more. Asked 6 years, 2 months ago. Active 3 years, 1 month ago. Viewed k times. I'm new to Android development and Android Studio, so pardon my ignorance. Duplicate of stackoverflow. Active Oldest Votes. Andy Res Andy Res BigT BigT 1, 4 4 gold badges 22 22 silver badges 48 48 bronze badges.
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