page.title=Improving Your Code with lint parent.title=Debugging parent.link=index.html @jd:body
In addition to testing that your Android application meets its functional requirements, it's important to ensure that your code has no structural problems. Poorly structured code can impact the reliability and efficiency of your Android apps and make your code harder to maintain. For example, if your XML resource files contain unused namespaces, this takes up space and incurs unnecessary processing. Other structural issues, such as use of deprecated elements or API calls that are not supported by the target API versions, might lead to code failing to run correctly.
The Android SDK provides a code scanning tool called lint
that can help you to easily identify and correct problems with the structural quality of your code, without having to execute the app or write any test cases. Each problem detected by the tool is reported with a description message and a severity level, so that you can quickly prioritize the critical improvements that need to be made. You can also configure a problem's severity level to ignore issues that are not relevant for your project, or raise the severity level. The tool has a command-line interface, so you can easily integrate it into your automated testing process.
The {@code lint} tool checks your Android project source files for potential bugs and optimization improvements for correctness, security, performance, usability, accessibility, and internationalization. You can run {@code lint} from the command-line or from Android Studio.
Note: In Android Studio, additional IntelliJ code inspections run when your code is compiled in Android Studio to streamline code review.
Figure 1 shows how the {@code lint} tool processes the application source files.
lint.xml
fileThe {@code lint} tool is automatically installed as part of the Android SDK Tools revision 16 or higher.
In Android Studio, the configured lint
and
IDE inspections run automatically whenever you build your app. The IDE inspections are
configured along with the {@code lint} checks to run
IntelliJ code inspections to streamline code review.
Note: To view and modify inspection severity levels, use the File > Settings > Project Settings menu to open the Inspection Configuration page with a list of the supported inspections.
With Android Studio, you can also run {@code lint} inspections for a specific build variant,
or for all build variants from the build.gradle
file. Add the
lintOptions
property to the android
settings in the build file.
This code snippet from a Gradle build file shows how to set the quiet
option to
true
and the abortOnError
option to false
.
android { lintOptions { // set to true to turn off analysis progress reporting by lint quiet true // if true, stop the gradle build if errors are found abortOnError false // if true, only report errors ignoreWarnings true } ... }
To manually run inspections in Android Studio, from the application or right-click menu, choose Analyze > Inspect Code. The Specify Inspections Scope dialog appears so you can specify the desired inspection scope and profile.
To run {@code lint} against a list of files in a project directory:
lint [flags] <project directory>
For example, you can issue the following command to scan the files under the {@code myproject} directory and its subdirectories. The issue ID MissingPrefix
tells {@code lint} to only scan for XML attributes that are missing the Android namespace prefix.
lint --check MissingPrefix myproject
To see the full list of flags and command-line arguments supported by the tool:
lint --help
The following example shows the console output when the {@code lint} command is run against a project called Earthquake.
$ lint Earthquake Scanning Earthquake: ............................................................................................................................... Scanning Earthquake (Phase 2): ....... AndroidManifest.xml:23: Warning: <uses-sdk> tag appears after <application> tag [ManifestOrder] <uses-sdk android:minSdkVersion="7" /> ^ AndroidManifest.xml:23: Warning: <uses-sdk> tag should specify a target API level (the highest verified version; when running on later versions, compatibility behaviors may be enabled) with android:targetSdkVersion="?" [UsesMinSdkAttributes] <uses-sdk android:minSdkVersion="7" /> ^ res/layout/preferences.xml: Warning: The resource R.layout.preferences appears to be unused [UnusedResources] res: Warning: Missing density variation folders in res: drawable-xhdpi [IconMissingDensityFolder] 0 errors, 4 warnings
The output above lists four warnings and no errors in this project. Three warnings ({@code ManifestOrder}, {@code UsesMinSdkAttributes}, and {@code UsesMinSdkAttributes}) were found in the project's AndroidManifest.xml
file. The remaining warning ({@code IconMissingDensityFolder}) was found in the Preferences.xml
layout file.
By default, when you run a {@code lint} scan, the tool checks for all issues that are supported by {@code lint}. You can also restrict the issues for {@code lint} to check and assign the severity level for those issues. For example, you can disable {@code lint} checking for specific issues that are not relevant to your project and configure {@code lint} to report non-critical issues at a lower severity level.
You can configure {@code lint} checking at different levels:
Android Studio allows you to enable or disable individual inspections and configure project-global, directory-specific, and file-specific settings for {@code lint}.
You can manage inspection profiles and configure inspection severity within Android Studio using the File > Settings > Project Settings menu to open the Inspections page with a list of the supported profiles and inspections.
The configured settings run the specified {@code lint} inspections. The {@code lint} inspections are also run whenever you build and run your Android project and modules.
You can specify your {@code lint} checking preferences in the lint.xml
file. If you are creating this file manually, place it in the root directory of your Android project. If you are configuring {@code lint} preferences in Android Studio, the lint.xml
file is automatically created and added to your Android project for you.
The lint.xml
file consists of an enclosing <lint>
parent tag that contains one or more children <issue>
elements. Each <issue>
is identified by a unique id
attribute value, which is defined by {@code lint}.
<?xml version="1.0" encoding="UTF-8"?> <lint> <!-- list of issues to configure --> </lint>
By setting the severity attribute value in the <issue>
tag, you can disable {@code lint} checking for an issue or change the severity level for an issue.
Tip: To see the full list of issues supported by the {@code lint} tool and their corresponding issue IDs, run the lint --list
command.
The following example shows the contents of a lint.xml
file.
<?xml version="1.0" encoding="UTF-8"?> <lint> <!-- Disable the given check in this project --> <issue id="IconMissingDensityFolder" severity="ignore" /> <!-- Ignore the ObsoleteLayoutParam issue in the specified files --> <issue id="ObsoleteLayoutParam"> <ignore path="res/layout/activation.xml" /> <ignore path="res/layout-xlarge/activation.xml" /> </issue> <!-- Ignore the UselessLeaf issue in the specified file --> <issue id="UselessLeaf"> <ignore path="res/layout/main.xml" /> </issue> <!-- Change the severity of hardcoded strings to "error" --> <issue id="HardcodedText" severity="error" /> </lint>
You can disable {@code lint} checking from your Java and XML source files.
Tip: If you are using Android Studio, you can use the File > Settings > Project Settings > Inspections feature to manage the {@code lint} checking to your Java or XML source files.
To disable {@code lint} checking specifically for a Java class or method in your Android project, add the @SuppressLint
annotation to that Java code.
The following example shows how you can turn off {@code lint} checking for the {@code NewApi} issue in the onCreate
method. The {@code lint} tool continues to check for the {@code NewApi} issue in other methods of this class.
@SuppressLint("NewApi") @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main);
The following example shows how to turn off {@code lint} checking for the {@code ParserError} issue in the FeedProvider
class:
@SuppressLint("ParserError") public class FeedProvider extends ContentProvider {
To suppress checking for all {@code lint} issues in the Java file, use the {@code all} keyword, like this:
@SuppressLint("all")
You can use the tools:ignore
attribute to disable {@code lint} checking for specific sections of your XML files. In order for this attribute to be recognized by the {@code lint} tool, the following namespace value must be included in your XML file:
namespace xmlns:tools="http://schemas.android.com/tools"
The following example shows how you can turn off {@code lint} checking for the {@code UnusedResources} issue for the <LinearLayout>
element of an XML layout file. The ignore
attribute is inherited by the children elements of the parent element in which the attribute is declared. In this example, the {@code lint} check is also disabled for the child <TextView>
element.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" tools:ignore="UnusedResources" > <TextView android:text="@string/auto_update_prompt" /> </LinearLayout>
To disable more than one issue, list the issues to disable in a comma-separated string. For example:
tools:ignore="NewApi,StringFormatInvalid"
To suppress checking for all {@code lint} issues in the XML element, use the {@code all} keyword, like this:
tools:ignore="all"