使用android SDK自带 Lint工具优化源码

Improving Your Code with lint

IN THIS DOCUMENT

Overview
Running lint from Eclipse
Running lint from the command-line
Configuring lint

Configuring lint in Eclipse
Configuring the lint file
Configuring lint checking in Java and XML source
files

SEE ALSO

lint (reference)

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.

Overview

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

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

lint

from the command-line or from the Eclipse environment.
Figure 1 shows how the

lint

tool processes the application source files.



Figure 1. Code scanning workflow with the

lint

tool
Application source filesThe source files consist of files that make up your Android project, including Java and XML files, icons, and ProGuard configuration files.The

lint.xml

fileA configuration file that you can use to specify any

lint

checks that you want to exclude and to customize problem severity
levels.The

lint

toolA static code scanning tool that you can run on your Android project from the command-line or from Eclipse. The

lint

tool
checks for structural code problems that could affect the quality and performance of your Android application. It is strongly recommended that you correct any errors that

lint

detects
before publishing your application.Results of

lint

checkingYou can view the results from

lint

in the console or in the Lint Warnings view in Eclipse. Each issue
is identified by the location in the source files where it occurred and a description of the issue.
The

lint

tool is automatically installed as part of the Android SDK Tools revision 16 or higher. If you want
to use

lint

in the Eclipse environment, you must also install the Android Development Tools (ADT) Plugin for Eclipse revision 16 or higher. For more information
about installing the SDK or the ADT Plugin for Eclipse, see Installing the SDK.

Running lint from Eclipse

If the ADT Plugin is installed in your Eclipse environment, the

lint

tool runs automatically when you perform
one of these actions:

Export an APK
Edit and save an XML source file in your Android project (such as a manifest or layout file)
Use the layout editor in Eclipse to make changes

Note that when you export an APK,

lint

only runs an automatic check for fatal errors and aborts the export if
fatal errors are found. You can turn off this automatic checking from the Lint Error Checking page in Eclipse Preferences.
The output is displayed in the Lint Warnings view. If the Lint Warnings view is not showing in the workbench, you can bring it up from the Eclipse menu by clicking Window
> Show View > Other > Android > Lint Warnings.
Figure 2 shows an example of the output in the Lint Warnings view.



Figure 2. Sample output in the Lint Warnings view
You can also run a

lint

scan manually on your Android project in Eclipse by right-clicking on the project folder
in the Package Explorer > Android Tools > Run Lint: Check for Common Errors.

Running lint from the Command-Line

To run

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

myproject

directory and its subdirectories.
The issue ID

MissingPrefix

tells

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

Example lint output

The following example shows the console output when the

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 (

ManifestOrder

,

UsesMinSdkAttributes

,
and

UsesMinSdkAttributes

) were found in the project's

AndroidManifest.xml

file.
The remaining warning (

IconMissingDensityFolder

) was found in the

Preferences.xml

layout
file.

Configuring lint

By default, when you run a

lint

scan, the tool checks for all issues that are supported by

lint

.
You can also restrict the issues for

lint

to check and assign the severity level for those issues. For example, you can disable

lint

checking
for specific issues that are not relevant to your project and configure

lint

to report non-critical issues at a lower severity level.
You can configure

lint

checking at different levels:

Globally, for all projects
Per project
Per file
Per Java class or method (by using the

@SuppressLint

annotation), or per XML element (by using the

tools:ignore

attribute.

Configuring lint in Eclipse

You can configure global, project-specific, and file-specific settings for

lint

from the Eclipse user interface.

Global preferences

Open Window > Preferences > Android > Lint Error Checking.
Specify your preferences and click OK.

These settings are applied by default when you run

lint

on your Android projects in Eclipse.

Project and file-specific preferences

Run the

lint

tool on your project by right-clicking on your project folder in the Package Explorer and selecting Android
Tools > Run Lint: Check for Common Errors. This action brings up the Lint Warnings view which displays a list of issues that

lint

detected
in your project.
From the Lint Warnings view, use the toolbar options to configure

lint

preferences for individual projects
and files in Eclipse. The options you can select include:

Suppress this error with an annotation/attribute - If the issue appears in a Java class, the

lint

tool adds
a

@SuppressLint

annotation to the method where the issue was detected. If the issue appears in an

.xml

file,

lint

inserts
a

tools:ignore

attribute to disable checking for the

lint

issue
in this file.
Ignore in this file - Disables checking for this

lint

issue in this file.
Ignore in this project - Disables checking for this

lint

issue in this project.
Always ignore - Disables checking for this

lint

issue globally for all projects.

If you select the second or third option, the

lint

tool automatically generates a

lint.xml

file
with these configuration settings in your Android application project folder.

Configuring the lint file

You can specify your

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

lint

preferences in Eclipse, 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

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

lint

checking
for an issue or change the severity level for an issue.

Tip: To see the full list of issues supported by the

lint

tool and their corresponding issue IDs, run the

lint
--list

command.

Sample lint.xml file

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>

Configuring lint checking in Java and XML source files

You can disable

lint

checking from your Java and XML source files.

Tip: If you are using Eclipse, you can use the Quick Fix feature to automatically add the annotation or attribute to disable

lint

checking
to your Java or XML source files:

Open the Java or XML file that has a

lint

warning or error in an Eclipse editor.
Move your cursor to the location in the file where is

lint

issue is found, then press

Ctrl+1

to
bring up the Quick Fixpop-up.
From the Quick Fix pop-up, select the action to add an annotation or attribute to ignore the

lint

issue.

Configuring lint checking in Java

To disable

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

lint

checking for the

NewApi

issue
in the

onCreate

method. The

lint

tool continues to
check for the

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

lint

checking for the

ParserError

issue
in the

FeedProvider

class:

@SuppressLint("ParserError")
public class FeedProvider extends ContentProvider {

To suppress checking for all

lint

issues in the Java file, use the

all

keyword,
like this:

@SuppressLint("all")

Configuring lint checking in XML

You can use the

tools:ignore

attribute to disable

lint

checking
for specific sections of your XML files. In order for this attribute to be recognized by the

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

lint

checking for the

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

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

lint

issues in the XML element, use the

all

keyword,
like this:

tools:ignore="all"

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