Fragment class not found

I’ve just started working on my first Android app and my focus is the main activity of the app, MathleteIDActivity, which includes a fragment TextFragment which displays some text.

The project builds fine, but crashes as soon as the app is launched. This happens on two different phones running Android 4.x.x, so fragment support shouldn’t be the issue. The stacktrace from adb logcat looks like this (package redacted):

java.lang.RuntimeException: Unable to start activity ComponentInfo{foo.bar.baz.id.MathleteIDActivity} ...
...
Caused by: android.view.InflateException: Binary XML file line #12: Error inflating class fragment
...
Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment .fragments.TextFragment: make sure class name exists, is public, and has an empty constructor that is public
...
Caused by: java.lang.ClassNotFoundException: .fragments.TextFragment
...

My directory structure seems kosher: I’ve got the package directories foo/bar/baz/ inside src/main/java/ in the project root, and within that package:

fragments/
    TextFragment.java
id/
    NFCIDActivity.java
    MathleteIDActivity.java
    ...
...

MathleteIDActivity.java reads as follows:

package foo.bar.baz.id;

import android.widget.TextView;
import android.os.Bundle;
import foo.bar.baz.R;

public final class MathleteIDActivity extends NFCIDActivity {
    @Override
    public void onCreate(Bundle savedState) {
        super.onCreate(savedState);
        TextView textView = (TextView) findViewById(R.id.fragment_text);
        textView.setText("Scan mathlete tag");
    }
}

NFCIDActivity is an abstract class that extends Android’s Activity. Its only method is an override of onCreate:

@Override
public void onCreate(Bundle savedState) {
    super.onCreate(savedState);
    setContentView(R.layout.id_activity);
}

And TextFragment.java reads as follows:

package foo.bar.baz.fragments;

import android.app.Fragment;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.view.LayoutInflater;
import foo.bar.baz.R;

public final class TextFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.text_fragment, container, false);
    }
}

In src/main/res/layout/id_activity.xml I have the activity layout defined:

<?xml version="1.0" encoding="utf-8" ?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <fragment
        android:name=".fragments.TextFragment"
        android:id="@+id/id_message" >
    </fragment>
</LinearLayout>

In the same directory, text_fragment.xml defines TextFragment‘s layout:

<?xml version="1.0" encoding="utf-8" ?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:id="@+id/fragment_text"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </TextView>
</LinearLayout>

I’ve already tried:

Adding a public, no-parameter constructor to TextFragment. Same errors.
Referencing the fragment in the layout file by its fully-qualified package name foo.bar.baz.fragments.TextFragment. Same errors, now naming the new package.
Moving TextFragment‘s source file to the top-level package foo.bar.baz and adjusting references. Same errors, now naming the new package.

Any ideas?

Answer

Instantiate your fragment programatically using FragmentManager as a quick solution:

FragmentManager fm = getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();

TextFragment tf = new TextFragment();
ft.replace(R.id.container, tf);
ft.commit();

As for your approach, use a canonical package name instead and clean-build your project. Then pay attention to the error message (it can’t be “same error” since it should at least mention different package name).

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Answer