FragmentNotInstantiable
Subclasses of Fragment must be instantiable via Class#newInstance(): the class must be public, static and have a public nullary constructor

Severity
WARNING
Tags
LikelyError
Has Fix?
NO_FIX

Alternate names: ValidFragment

The problem

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("FragmentNotInstantiable") to the enclosing element.


Positive examples

FragmentNotInstantiablePositiveCases.java

/*
* Copyright 2016 The Error Prone Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/


package com.google.errorprone.bugpatterns.android.testdata;

import android.app.Fragment;

/** @author avenet@google.com (Arnaud J. Venet) */
public class FragmentNotInstantiablePositiveCases {
// BUG: Diagnostic contains: public
static class PrivateFragment extends Fragment {
public PrivateFragment() {}
}

// BUG: Diagnostic contains: public
static class PrivateV4Fragment extends android.support.v4.app.Fragment {
public PrivateV4Fragment() {}
}

public static class PrivateConstructor extends Fragment {
// BUG: Diagnostic contains: public
PrivateConstructor() {}
}

// BUG: Diagnostic contains: nullary constructor
public static class NoConstructor extends Fragment {
public NoConstructor(int x) {}
}

// BUG: Diagnostic contains: nullary constructor
public static class NoConstructorV4 extends android.support.v4.app.Fragment {
public NoConstructorV4(int x) {}
}

public static class ParentFragment extends Fragment {
public ParentFragment() {}
}

public static class ParentFragmentV4 extends android.support.v4.app.Fragment {
public ParentFragmentV4() {}
}

// BUG: Diagnostic contains: nullary constructor
public static class DerivedFragmentNoConstructor extends ParentFragment {
public DerivedFragmentNoConstructor(int x) {}
}

// BUG: Diagnostic contains: nullary constructor
public static class DerivedFragmentNoConstructorV4 extends ParentFragmentV4 {
public DerivedFragmentNoConstructorV4(boolean b) {}
}

public class EnclosingClass {
// BUG: Diagnostic contains: static
public class InnerFragment extends Fragment {
public InnerFragment() {}
}

public Fragment create1() {
// BUG: Diagnostic contains: public
return new Fragment() {};
}

public Fragment create2() {
// BUG: Diagnostic contains: public
class LocalFragment extends Fragment {}
return new LocalFragment();
}
}
}

Negative examples

FragmentNotInstantiableNegativeCases.java

/*
* Copyright 2016 The Error Prone Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/


package com.google.errorprone.bugpatterns.android.testdata;

import android.app.Fragment;

/** @author avenet@google.com (Arnaud J. Venet) */
public class FragmentNotInstantiableNegativeCases {
public static class NotAFragment1 {
public NotAFragment1(int x) {}
}

public static class NotAFragment2 {
private NotAFragment2() {}
}

private static class NotAFragment3 {}

public class NotAFragment4 {}

private abstract class AbstractFragment extends Fragment {
public AbstractFragment(int x) {}
}

private abstract class AbstractV4Fragment extends android.support.v4.app.Fragment {
private int a;

public int value() {
return a;
}
}

public static class MyFragment extends Fragment {
private int a;

public int value() {
return a;
}
}

public static class DerivedFragment extends MyFragment {}

public static class MyV4Fragment extends android.support.v4.app.Fragment {}

public static class DerivedV4Fragment extends MyV4Fragment {
private int a;

public int value() {
return a;
}
}

public static class MyFragment2 extends Fragment {
public MyFragment2() {}

public MyFragment2(int x) {}
}

public static class DerivedFragment2 extends MyFragment2 {
public DerivedFragment2() {}

public DerivedFragment2(boolean b) {}
}

public static class EnclosingClass {
public static class InnerFragment extends Fragment {
public InnerFragment() {}
}
}

interface AnInterface {
public class ImplicitlyStaticInnerFragment extends Fragment {}

class ImplicitlyStaticAndPublicInnerFragment extends Fragment {}
}
}