com.android.tools.lint.checks.ViewHolderDetector Maven / Gradle / Ivy
/*
* Copyright (C) 2014 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.VIEW;
import static com.android.SdkConstants.VIEW_GROUP;
import static com.android.tools.lint.client.api.JavaParser.TYPE_INT;
import com.android.annotations.NonNull;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Detector;
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.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.android.tools.lint.detector.api.Speed;
import com.google.common.collect.Lists;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import lombok.ast.AstVisitor;
import lombok.ast.ForwardingAstVisitor;
import lombok.ast.If;
import lombok.ast.InlineIfExpression;
import lombok.ast.MethodDeclaration;
import lombok.ast.MethodInvocation;
import lombok.ast.Node;
import lombok.ast.StrictListAccessor;
import lombok.ast.Switch;
import lombok.ast.VariableDefinition;
/**
* Looks for ListView scrolling performance: should use view holder pattern
*/
public class ViewHolderDetector extends Detector implements Detector.JavaScanner {
private static final Implementation IMPLEMENTATION = new Implementation(
ViewHolderDetector.class,
Scope.JAVA_FILE_SCOPE);
/** Using a view inflater unconditionally in an AdapterView */
public static final Issue ISSUE = Issue.create(
"ViewHolder", //$NON-NLS-1$
"View Holder Candidates",
"When implementing a view Adapter, you should avoid unconditionally inflating a " +
"new layout; if an available item is passed in for reuse, you should try to " +
"use that one instead. This helps make for example ListView scrolling much " +
"smoother.",
Category.PERFORMANCE,
5,
Severity.WARNING,
IMPLEMENTATION)
.addMoreInfo(
"http://developer.android.com/training/improving-layouts/smooth-scrolling.html#ViewHolder");
private static final String GET_VIEW = "getView"; //$NON-NLS-1$
static final String INFLATE = "inflate"; //$NON-NLS-1$
/** Constructs a new {@link ViewHolderDetector} check */
public ViewHolderDetector() {
}
@NonNull
@Override
public Speed getSpeed() {
return Speed.NORMAL;
}
// ---- Implements JavaScanner ----
@Override
public List> getApplicableNodeTypes() {
return Collections.>singletonList(MethodDeclaration.class);
}
@Override
public AstVisitor createJavaVisitor(@NonNull JavaContext context) {
return new ViewAdapterVisitor(context);
}
private static class ViewAdapterVisitor extends ForwardingAstVisitor {
private final JavaContext mContext;
public ViewAdapterVisitor(JavaContext context) {
mContext = context;
}
@Override
public boolean visitMethodDeclaration(MethodDeclaration node) {
if (isViewAdapterMethod(node)) {
InflationVisitor visitor = new InflationVisitor(mContext);
node.accept(visitor);
visitor.finish();
}
return super.visitMethodDeclaration(node);
}
/**
* Returns true if this method looks like it's overriding android.widget.Adapter's getView
* method: getView(int position, View convertView, ViewGroup parent)
*/
private static boolean isViewAdapterMethod(MethodDeclaration node) {
if (GET_VIEW.equals(node.astMethodName().astValue())) {
StrictListAccessor parameters =
node.astParameters();
if (parameters != null && parameters.size() == 3) {
Iterator iterator = parameters.iterator();
if (!iterator.hasNext()) {
return false;
}
VariableDefinition first = iterator.next();
if (!first.astTypeReference().astParts().last().getTypeName().equals(
TYPE_INT)) {
return false;
}
if (!iterator.hasNext()) {
return false;
}
VariableDefinition second = iterator.next();
if (!second.astTypeReference().astParts().last().getTypeName().equals(
VIEW)) {
return false;
}
if (!iterator.hasNext()) {
return false;
}
VariableDefinition third = iterator.next();
//noinspection RedundantIfStatement
if (!third.astTypeReference().astParts().last().getTypeName().equals(
VIEW_GROUP)) {
return false;
}
return true;
}
}
return false;
}
}
private static class InflationVisitor extends ForwardingAstVisitor {
private final JavaContext mContext;
private List mNodes;
private boolean mHaveConditional;
public InflationVisitor(JavaContext context) {
mContext = context;
}
@Override
public boolean visitMethodInvocation(MethodInvocation node) {
if (node.astOperand() != null) {
String methodName = node.astName().astValue();
if (methodName.equals(INFLATE) && node.astArguments().size() >= 1) {
// See if we're inside a conditional
boolean insideIf = false;
Node p = node.getParent();
while (p != null) {
if (p instanceof If || p instanceof InlineIfExpression
|| p instanceof Switch) {
insideIf = true;
mHaveConditional = true;
break;
} else if (p == node) {
break;
}
p = p.getParent();
}
if (!insideIf) {
// Rather than reporting immediately, we only report if we didn't
// find any conditionally executed inflate statements in the method.
// This is because there are cases where getView method is complicated
// and inflates not just the top level layout but also children
// of the view, and we don't want to flag these. (To be more accurate
// should perform flow analysis and only report unconditional inflation
// of layouts that wind up flowing to the return value; that requires
// more work, and this simple heuristic is good enough for nearly all test
// cases I've come across.
if (mNodes == null) {
mNodes = Lists.newArrayList();
}
mNodes.add(node);
}
}
}
return super.visitMethodInvocation(node);
}
public void finish() {
if (!mHaveConditional && mNodes != null) {
for (Node node : mNodes) {
String message = "Unconditional layout inflation from view adapter: "
+ "Should use View Holder pattern (use recycled view passed "
+ "into this method as the second parameter) for smoother "
+ "scrolling";
mContext.report(ISSUE, node, mContext.getLocation(node), message);
}
}
}
}
}