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.CONSTRUCTOR_NAME;
import static com.android.SdkConstants.FRAGMENT;
import static com.android.SdkConstants.FRAGMENT_V4;
import com.android.annotations.NonNull;
import com.android.tools.lint.client.api.LintDriver;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.ClassContext;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Detector.ClassScanner;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.LintUtils;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.android.tools.lint.detector.api.Speed;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.MethodNode;
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 ClassScanner {
private static final String FRAGMENT_NAME_SUFFIX = "Fragment"; //$NON-NLS-1$
/** Are fragment subclasses instantiatable? */
public static final Issue ISSUE = Issue.create(
"ValidFragment", //$NON-NLS-1$
"Fragment not instantiatable",
"Ensures that `Fragment` subclasses can be instantiated",
"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.ERROR,
new Implementation(
FragmentDetector.class,
Scope.CLASS_FILE_SCOPE)
).addMoreInfo(
"http://developer.android.com/reference/android/app/Fragment.html#Fragment()"); //$NON-NLS-1$
/** Constructs a new {@link FragmentDetector} */
public FragmentDetector() {
}
@NonNull
@Override
public Speed getSpeed() {
return Speed.FAST;
}
// ---- Implements ClassScanner ----
@Override
public void checkClass(@NonNull ClassContext context, @NonNull ClassNode classNode) {
if ((classNode.access & Opcodes.ACC_ABSTRACT) != 0) {
// Ignore abstract classes since they are clearly (and by definition) not intended to
// be instantiated. We're looking for accidental non-static or missing constructor
// scenarios here.
return;
}
LintDriver driver = context.getDriver();
if (!(driver.isSubclassOf(classNode, FRAGMENT)
|| driver.isSubclassOf(classNode, FRAGMENT_V4))) {
return;
}
if ((classNode.access & Opcodes.ACC_PUBLIC) == 0) {
context.report(ISSUE, context.getLocation(classNode), String.format(
"This fragment class should be public (%1$s)",
ClassContext.createSignature(classNode.name, null, null)),
null);
return;
}
if (classNode.name.indexOf('$') != -1 && !LintUtils.isStaticInnerClass(classNode)) {
context.report(ISSUE, context.getLocation(classNode), String.format(
"This fragment inner class should be static (%1$s)",
ClassContext.createSignature(classNode.name, null, null)),
null);
return;
}
boolean hasDefaultConstructor = false;
@SuppressWarnings("rawtypes") // ASM API
List methodList = classNode.methods;
for (Object m : methodList) {
MethodNode method = (MethodNode) m;
if (method.name.equals(CONSTRUCTOR_NAME)) {
if (method.desc.equals("()V")) { //$NON-NLS-1$
// The constructor must be public
if ((method.access & Opcodes.ACC_PUBLIC) != 0) {
hasDefaultConstructor = true;
} else {
context.report(ISSUE, context.getLocation(method, classNode),
"The default constructor must be public",
null);
// 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 if (!method.desc.contains("()")) { //$NON-NLS-1$
context.report(ISSUE, context.getLocation(method, classNode),
// TODO: Use separate issue for this which isn't an error
"Avoid non-default constructors in fragments: use a default constructor " +
"plus Fragment#setArguments(Bundle) instead",
null);
}
}
}
if (!hasDefaultConstructor) {
context.report(ISSUE, context.getLocation(classNode), String.format(
"This fragment should provide a default constructor (a public " +
"constructor with no arguments) (%1$s)",
ClassContext.createSignature(classNode.name, null, null)),
null);
}
}
}