Develop Reference

Possible reason for "Error:cannot generate view binders java.lang.NullPointerException"

I am using Android Studio for my Android projects. I faced an issue when builds crash with strange stacktrace, like this:
Error:Execution failed for task ':app:compileDevDebugJavaWithJavac'.
java.lang.RuntimeException: failure, see logs for details.
cannot generate view binders java.lang.NullPointerException
at android.databinding.tool.reflection.ModelMethod.isBoxingConversion(ModelMethod.java:155)
at android.databinding.tool.store.SetterStore.isBetterParameter(SetterStore.java:946)
at android.databinding.tool.store.SetterStore.getBestSetter(SetterStore.java:838)
and it was seemed that the databinding became broken as whole.
I made refactoring before and moved classes between packages.

In my case, I relied on Android Studio when renaming and moving classes between packages. But it didn't proceed correction for XMLs of layouts where were references on refactored classes in the type attribute of variable element in data.
So my previous type's value pointed to non existing files and build crashed.
It's simple mistake but it may take more time to find the source. Hope this would help someone.

For me, this started happening after updating Android Studio to version 3.5.2
To fix it, I downgraded Android Gradle Plugin
buildscript {
repositories {
//..........
}
dependencies {
classpath 'com.android.tools.build:gradle:3.5.1'
//......
}
}

Make sure you import all classes you reference in xml bindings
I had code something like:
android:visible="#{obj instanceof A}"
I was getting that same error.
Turns out that class A was not imported on top. Adding <import type="com.company.A"> tag resolved the problem.
P.S. android:visible is a custom binding adapter I have.

If this question is still relevant. For me I figured that in my xml layout file I was including a class (not an instance of one) as a variable, i.e I had this code
<variable
name="Converters"
type="com.example.flexapp.utils.Converters" />
and it should have been
<import type="com.example.flexapp.utils.Converters"/>
since this was a class and not an object.

in my case my problem was in a LongClickListener that the method for this listener must have returned a boolean but my method returned void so when I added the correct return statement it worked just fine.
keep in mind if you use a data binding method you must return the correct value or else the error it throws is not helpful at all.

You may have stumbled upon this question after migrating to Android X. If that's the case, and you're positive your XML files are okay, but it's still not working, you should start looking at libraries that generate code.
Libraries that generate code cannot be easily converted by the Jettifyer. Some info here - https://blog.danlew.net/2018/11/14/the-reality-of-migrating-to-androidx/
In my case, I updated the obvious ones, but I still was missing something. So, what I did was go into my develop branch (that wasn't Android X), ran a build, and dug into the build folder to see all of the libraries that generated code. Once I did that, I was able to look at the suspects one by one until I found the dependency that was causing this issue. You could either update it, or, in my case, remove it, and this error was resolved. :)

The getter function for any instance that you refer from your xml file might not have been defined or the getter function might not have public access specifier.

Downgrading Android Gradle Plugin to 3.5.1 fixed the issue for me

I face this problem when I define variable like this (Android Studio don't warning anything)
<data>
<variable
name="onGlobalLayoutA"
type="ViewTreeObserver.OnGlobalLayoutListener"/>
<import type="android.view.ViewTreeObserver"/>
</data>
And I solve it by
<data>
<variable
name="onGlobalLayoutA"
type="android.view.ViewTreeObserver.OnGlobalLayoutListener"/>
</data>
Hope this would help someone.

In my case, the reason was that I used a type for a variable which is another module and that module is added as 'implementation ' in build script. Changing to 'api ' resolved the issue.
Clearly not the same issue as the one posted by atlascoder but I mention regardless, maybe someone gits this article with the same problem as I had.

As #hiddeneyes02 mentioned, this started happen when upgrading from Android Gradle Plugin from 3.5.1 to 3.5.2, this seems to be the bug:
https://issuetracker.google.com/issues/143778134
When I built the project with the command tool I got the same errors as in this post:
When building Android project with Android Gradle Plugin v. 3.5.2 my builds fail

In my case I wrote wrong the name of my view model variable inside the XML file. I had it named VProgressBar instead of vProgressBar:
android:visibility="#{fatherViewModel.vProgressBar}"

Android : Activity error in other package

This is my project stricture :
-com.android.test
--com.android.test.activity
---MainActivity.java
---SplashActivity.java
--com.android.test.ui
---ActivityBase.java
I created all activity in com.android.test.activity package and all activities extended from Base activity in com.android.test.ui package
But i don't know , when i creating activities on com.android.test.activity i see .R error in my Eclips , but when i creating activity on com.android.test package ,no need for importing the .R class.
I'm very beginner , please help

When you build an android project, the build tools generate a class called R.java. Because R is a class, it will exist in a package, just like all your other classes. By default, R will be generated in the package you've specified as the project package. For you, this should be com.android.test.
So your package structure is actually like this, even though R is in gen/, not src/.
-com.android.test
--R.java
--com.android.test.activity
---MainActivity.java
---SplashActivity.java
--com.android.test.ui
---ActivityBase.java
In Java, you will require an import statement if a class is not declared inside the package of the current class. So because com.android.test is not contained in com.android.test.activity, you will need to add import com.android.test.R; to MainActivity and SplashActivity, in order to use R in them.
If R is not being generated for you, check out Developing for Android in Eclipse: R.java not regenerating. I would possibly recommend learning to use IntelliJ IDEA, as I've encountered fewer strange build issues than in eclipse, but this is completely optional.
Another possible source of error is if you accidentally imported android.R, which is where the resources of the android SDK are referenced from. This could easily mess you up, since you could write code like R.string.foo and think you are using com.android.test.R.string.foo, but in reality, you are using android.R.string.foo, which may not exist. An easy way to find the problem is to explicitly say in your code, for example:
// you were originally getting an error here
MyActivity.this.getString(R.string.foo);
// try this to get a more obvious error, or see if it fixes it
MyActivity.this.getString(com.android.test.R.string.foo);

Error with R.java class, layout no found but present in R.java

Well, first I'm sorry but my english is not very good because I'm French...
I work on Eclipse on an android project (pong)
So, I've a problem with an activity, when I write : setContentView(R.layout.menu);
I have an error who say : menu cannot be resolved or is not a field
The fact is... This is a file ! I went to the R.java and I see it, but the error don't disappear. (I have alredy clean and build the project many times, it still don't work)
I have took some screens ;-)
http://imageshack.us/photo/my-images/4/erreurmenupong1.png/ (In the Menu.java)
http://imageshack.us/photo/my-images/62/erreurmenupong2.png/ (In the R.java)

Delete "android.R" from your imports.

I had the same exact problem. I solved it buy making a new work space and importing all my android projects over there.

Android Facebook sdk Session.OpenRequest(myFragment) is undefined?

For some reason I cannot see the line of code:
session = new Session.OpenRequest(this).setCallBack(statusCallBack)
It gives me an error that Session.OpenRequest(myFragment) is undefined. Does anyone know why this is and how I can fix it?

Found out what i was doing wrong. It has to be a fragment from the support library. I was extending the regular fragment class.

Apparently, Session.OpenRequest(Fragment fragment) constructor should work. Assuming that you have added Facebook SDK properly in your project, organize the imports in your class to import the Session.OpenRequest class. This constructor seems to be invisible for your code.
If you are using Eclipse IDE organize imports by pressing Ctrl+Shift+O.

NoClassDefFoundError Android with ActionBarActivity

I currently have an ActionBarActivity which always returns a NoClassDefFoundError. I've read that it might be a problem with the ADT but I cannot be sure, hence my question. I've imported the ActionBar sample from the Android samples under
android-sdk\samples\android-14\ActionBarCompat
I've labelled the ActionBarCompat project as a library under Project -> Properties but I'm still getting the error.
To reiterator:
public class SearchActivity extends ActionBarActivity { // Doesn't work, yields exception
public class SearchActivity extends Activity { // Works perfectly
Has anyone else experienced a similar error and perhaps found a solution?
Thanks in advance.

http://developer.android.com/tools/support-library/setup.html
The "Adding libraries with resources" section may help
since this is not in the most common v4 support library
include only android-support-v4.jar is not enough

Ended up using ActionBarSherlock instead and added a project reference under Project Properties as well as in the Build Path. Seems to have fixed all errors relating to my question.

Just this morning, Google released Android 4.3. They also updated its support library that allows ActionBar to be implemented on lower versions. Just have to extend ActionBarActivity. See guidelines here and tutorial here.

I've got the same problem. I solved it getting the android-support-v7-appcompat.jar library.
See here http://developer.android.com/tools/support-library/setup.html#using-apis how to install it.
I recommend focus on "Adding libraries without resources" instead "Adding libraries with resources" for the sake of simplicity.
When you do it, don't forget to import the this library into your Activity Java source. You can do it declaring import android.support.v7.app.ActionBarActivity;

I solved this problem like so, when you add the library make sure it does not have the android-support-v4 along with it (in libs folder of the library un-check android dependencies and android-support-v4), that's in the case where your project already have the android-support-v4, that's why you can't find class ActionBarActivity

This Link
may help you.
This library is located in the /extras/android/support/v7/appcompat/ directory.
Include in eclipse and add as library. This will solve your problem.