com.android.tools.lint.checks.FragmentDetector Maven / Gradle / Ivy
/*
* Copyright (C) 2012 The Android Open Source Project
*
* 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.android.tools.lint.checks;
import static com.android.SdkConstants.CLASS_FRAGMENT;
import static com.android.SdkConstants.CLASS_V4_FRAGMENT;
import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.android.tools.lint.client.api.JavaEvaluator;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Detector.JavaPsiScanner;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.JavaContext;
import com.android.tools.lint.detector.api.Location;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.intellij.psi.PsiAnonymousClass;
import com.intellij.psi.PsiClass;
import com.intellij.psi.PsiElement;
import com.intellij.psi.PsiMethod;
import java.util.Arrays;
import java.util.List;
/**
* Checks that Fragment subclasses can be instantiated via
* {link {@link Class#newInstance()}}: the class is public, static, and has
* a public null constructor.
*
* This helps track down issues like
* http://stackoverflow.com/questions/8058809/fragment-activity-crashes-on-screen-rotate
* (and countless duplicates)
*/
public class FragmentDetector extends Detector implements JavaPsiScanner {
/** Are fragment subclasses instantiatable? */
public static final Issue ISSUE = Issue.create(
"ValidFragment", //$NON-NLS-1$
"Fragment not instantiatable",
"From the Fragment documentation:\n" +
"*Every* fragment must have an empty constructor, so it can be instantiated when " +
"restoring its activity's state. It is strongly recommended that subclasses do not " +
"have other constructors with parameters, since these constructors will not be " +
"called when the fragment is re-instantiated; instead, arguments can be supplied " +
"by the caller with `setArguments(Bundle)` and later retrieved by the Fragment " +
"with `getArguments()`.",
Category.CORRECTNESS,
6,
Severity.FATAL,
new Implementation(
FragmentDetector.class,
Scope.JAVA_FILE_SCOPE)
).addMoreInfo(
"http://developer.android.com/reference/android/app/Fragment.html#Fragment()"); //$NON-NLS-1$
/** Constructs a new {@link FragmentDetector} */
public FragmentDetector() {
}
// ---- Implements JavaScanner ----
@Nullable
@Override
public List applicableSuperClasses() {
return Arrays.asList(CLASS_FRAGMENT, CLASS_V4_FRAGMENT);
}
@Override
public void checkClass(@NonNull JavaContext context, @NonNull PsiClass node) {
if (node instanceof PsiAnonymousClass) {
String message = "Fragments should be static such that they can be re-instantiated by " +
"the system, and anonymous classes are not static";
PsiElement locationNode = JavaContext.findNameElement(node);
if (locationNode == null) {
locationNode = node;
}
context.report(ISSUE, locationNode, context.getLocation(locationNode), message);
return;
}
JavaEvaluator evaluator = context.getEvaluator();
if (evaluator.isAbstract(node)) {
return;
}
if (!evaluator.isPublic(node)) {
String message = String.format("This fragment class should be public (%1$s)",
node.getQualifiedName());
context.report(ISSUE, node, context.getNameLocation(node), message);
return;
}
if (node.getContainingClass() != null && !evaluator.isStatic(node)) {
String message = String.format(
"This fragment inner class should be static (%1$s)", node.getQualifiedName());
context.report(ISSUE, node, context.getNameLocation(node), message);
return;
}
boolean hasDefaultConstructor = false;
boolean hasConstructor = false;
for (PsiMethod constructor : node.getConstructors()) {
hasConstructor = true;
if (constructor.getParameterList().getParametersCount() == 0) {
if (evaluator.isPublic(constructor)) {
hasDefaultConstructor = true;
} else {
Location location = context.getNameLocation(constructor);
context.report(ISSUE, constructor, location,
"The default constructor must be public");
// Also mark that we have a constructor so we don't complain again
// below since we've already emitted a more specific error related
// to the default constructor
hasDefaultConstructor = true;
}
} else {
Location location = context.getNameLocation(constructor);
// TODO: Use separate issue for this which isn't an error
String message = "Avoid non-default constructors in fragments: "
+ "use a default constructor plus "
+ "`Fragment#setArguments(Bundle)` instead";
context.report(ISSUE, constructor, location, message);
}
}
if (!hasDefaultConstructor && hasConstructor) {
String message = String.format(
"This fragment should provide a default constructor (a public " +
"constructor with no arguments) (`%1$s`)",
node.getQualifiedName());
context.report(ISSUE, node, context.getNameLocation(node), message);
}
}
}