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

/*
 * Copyright (C) 2011 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_BACKGROUND;
import static com.android.SdkConstants.ATTR_LAYOUT_WEIGHT;
import static com.android.SdkConstants.ATTR_SCALE_TYPE;
import static com.android.SdkConstants.IMAGE_VIEW;
import static com.android.SdkConstants.LINEAR_LAYOUT;
import static com.android.SdkConstants.TEXT_VIEW;

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.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 com.android.tools.lint.detector.api.XmlContext;

import org.w3c.dom.Element;

import java.util.Collection;
import java.util.Collections;
import java.util.List;

/**
 * Checks whether the current node can be replaced by a TextView using compound
 * drawables.
 */
public class UseCompoundDrawableDetector extends LayoutDetector {
    /** The main issue discovered by this detector */
    public static final Issue ISSUE = Issue.create(
            "UseCompoundDrawables", //$NON-NLS-1$
            "Node can be replaced by a `TextView` with compound drawables",

            "A `LinearLayout` which contains an `ImageView` and a `TextView` can be more " +
            "efficiently handled as a compound drawable (a single TextView, using the " +
            "`drawableTop`, `drawableLeft`, `drawableRight` and/or `drawableBottom` attributes " +
            "to draw one or more images adjacent to the text).\n" +
            "\n" +
            "If the two widgets are offset from each other with " +
            "margins, this can be replaced with a `drawablePadding` attribute.\n" +
            "\n" +
            "There's a lint quickfix to perform this conversion in the Eclipse plugin.",
            Category.PERFORMANCE,
            6,
            Severity.WARNING,
            new Implementation(
                    UseCompoundDrawableDetector.class,
                    Scope.RESOURCE_FILE_SCOPE));

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

    @NonNull
    @Override
    public Speed getSpeed() {
        return Speed.FAST;
    }

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

    @Override
    public void visitElement(@NonNull XmlContext context, @NonNull Element element) {
        int childCount = LintUtils.getChildCount(element);
        if (childCount == 2) {
            List<Element> children = LintUtils.getChildren(element);
            Element first = children.get(0);
            Element second = children.get(1);
            if ((first.getTagName().equals(IMAGE_VIEW) &&
                    second.getTagName().equals(TEXT_VIEW) &&
                    !first.hasAttributeNS(ANDROID_URI, ATTR_LAYOUT_WEIGHT)) ||
                ((second.getTagName().equals(IMAGE_VIEW) &&
                        first.getTagName().equals(TEXT_VIEW) &&
                        !second.hasAttributeNS(ANDROID_URI, ATTR_LAYOUT_WEIGHT)))) {
                // If the layout has a background, ignore since it would disappear from
                // the TextView
                if (element.hasAttributeNS(ANDROID_URI, ATTR_BACKGROUND)) {
                    return;
                }

                // Certain scale types cannot be done with compound drawables
                String scaleType = first.getTagName().equals(IMAGE_VIEW)
                        ? first.getAttributeNS(ANDROID_URI, ATTR_SCALE_TYPE)
                        : second.getAttributeNS(ANDROID_URI, ATTR_SCALE_TYPE);
                if (scaleType != null && !scaleType.isEmpty()) {
                    // For now, ignore if any scale type is set
                    return;
                }

                context.report(ISSUE, element, context.getLocation(element),
                        "This tag and its children can be replaced by one `<TextView/>` and " +
                                "a compound drawable");
            }
        }
    }
}