lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/MissingIdDetector.java

/*
 * 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.ANDROID_URI;
import static com.android.SdkConstants.ATTR_ID;
import static com.android.SdkConstants.ATTR_TAG;
import static com.android.SdkConstants.VIEW_FRAGMENT;

import com.android.annotations.NonNull;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.LayoutDetector;
import com.android.tools.lint.detector.api.LintFix;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.android.tools.lint.detector.api.XmlContext;
import java.util.Collection;
import java.util.Collections;
import org.w3c.dom.Element;

/** Check which looks for missing id's in views where they are probably needed */
public class MissingIdDetector extends LayoutDetector {
    /** The main issue discovered by this detector */
    public static final Issue ISSUE =
            Issue.create(
                            "MissingId",
                            "Fragments should specify an `id` or `tag`",
                            "If you do not specify an `android:id` or an `android:tag` attribute on a "
                                    + "`<fragment>` element, then if the activity is restarted (for example for "
                                    + "an orientation rotation) you may lose state. From the fragment "
                                    + "documentation:\n"
                                    + "\n"
                                    + "\"Each fragment requires a unique identifier that the system can use "
                                    + "to restore the fragment if the activity is restarted (and which you can "
                                    + "use to capture the fragment to perform transactions, such as remove it).\n"
                                    + "\n"
                                    + "* Supply the `android:id` attribute with a unique ID.\n"
                                    + "* Supply the `android:tag` attribute with a unique string.\n"
                                    + "If you provide neither of the previous two, the system uses the ID of the "
                                    + "container view.",
                            Category.CORRECTNESS,
                            5,
                            Severity.WARNING,
                            new Implementation(MissingIdDetector.class, Scope.RESOURCE_FILE_SCOPE))
                    .addMoreInfo("https://developer.android.com/guide/components/fragments.html");

    /** Constructs a new {@link MissingIdDetector} */
    public MissingIdDetector() {}

    @Override
    public Collection<String> getApplicableElements() {
        return Collections.singletonList(VIEW_FRAGMENT);
    }

    @Override
    public void visitElement(@NonNull XmlContext context, @NonNull Element element) {
        if (!element.hasAttributeNS(ANDROID_URI, ATTR_ID)
                && !element.hasAttributeNS(ANDROID_URI, ATTR_TAG)) {
            LintFix fix = fix().set().todo(ANDROID_URI, ATTR_ID, "@+id/", null).build();
            context.report(
                    ISSUE,
                    element,
                    context.getNameLocation(element),
                    "This `<fragment>` tag should specify an id or a tag to preserve state "
                            + "across activity restarts",
                    fix);
        }
    }
}