Android 性能优化(1)性能工具之「 lint 」 :Improving Your Code with lint:优化代码
Improving Your Code with lint
1.See Also
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.
2.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 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 lint
tool processes the application source files.
![](https://images2015.cnblogs.com/blog/725063/201604/725063-20160405221212875-517593112.png)
Figure 1. Code scanning workflow with the lint
tool
- Application source files
- The source files consist of files that make up your Android project, including Java and XML files, icons, and ProGuard configuration files.
- The
lint.xml
file - A configuration file that you can use to specify any
lint
checks that you want to exclude and to customize problem severity levels. - The
lint
tool - A static code scanning tool that you can run on your Android project from the command-line or Android Studio. 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 thatlint
detects before publishing your application. - Results of
lint
checking - You can view the results from
lint
in the console or in the Event Log in Android Studio. 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.
3.Running lint in Android Studio
In Android Studio, the configured lint
and IDE inspections run automatically whenever you build your app. The IDE inspections are configured along with the 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 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
.
在AS中如何运行Lint工具
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.
4.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 UnusedResources
) were found in the project's AndroidManifest.xml
file. The remaining warning (IconMissingDensityFolder
) was found in the Preferences.xml
layout file.
5.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:
Lint 扫描选项配置等级:
- Globally, for the entire project
- Per project module
- Per production module
- Per test module
- Per open files
- Per class hierarchy
- Per Version Control System (VCS) scopes
5.1 Configuring lint in Android Studio (在AS中配置Lint扫描选项)
Android Studio allows you to enable or disable individual inspections and configure project-global, directory-specific, and file-specific settings for 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.
配置页面在: File > Settings > Editor > Inspections > Android Lint
Figure 3. Inspection Configuration
也可以扫描项目后,然后针对某个选项进行配置, 在Inspection 页面 > 右键某个选项 > Eidt Settings 就可以弹出针对该选项的设置,如图:
Global preferences (扫描整个项目)
- To specify global project settings, select the project folder in the Project View and choose Analyze > Inspect Code.
- Specify your inspection scope and profile, and click OK.
The configured settings run the specified lint
inspections. The lint
inspections are also run whenever you build and run your Android project and modules.
Module and file-specific preferences (扫描某模块或文件)
- Run the
lint
tool on your module by right-clicking on your module folder or file in the Project View and selecting Analyze > Inspect Code. This displays thelint
inspection results with a list of issues thatlint
detected in your module. - From the Lint Warnings view, use the toolbar options to configure
lint
preferences for individual modules and files, and set the issue display options.
5.2 Configuring the lint file (用lint.xml配置扫描选项)
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 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 lint
.
1 <?xml version="1.0" encoding="UTF-8"?> 2 <lint> 3 <!-- list of issues to configure --> 4 </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.
可以通过 命令 $lint --list 查看配置选项
Sample lint.xml file (lint.xml示例)
The following example shows the contents of a lint.xml
file.
1 <?xml version="1.0" encoding="UTF-8"?> 2 <lint> 3 <!-- Disable the given check in this project --> 4 <issue id="IconMissingDensityFolder" severity="ignore" /> 5 6 <!-- Ignore the ObsoleteLayoutParam issue in the specified files --> 7 <issue id="ObsoleteLayoutParam"> 8 <ignore path="res/layout/activation.xml" /> 9 <ignore path="res/layout-xlarge/activation.xml" /> 10 </issue> 11 12 <!-- Ignore the UselessLeaf issue in the specified file --> 13 <issue id="UselessLeaf"> 14 <ignore path="res/layout/main.xml" /> 15 </issue> 16 17 <!-- Change the severity of hardcoded strings to "error" --> 18 <issue id="HardcodedText" severity="error" /> 19 </lint>
5.3 Configuring lint checking in Java and XML source files (如何忽略 .java 和 .xml 等源文件中的lint提示)
You can disable lint
checking from your Java and XML source files.
下面是在AS中的配置方法:
Tip: If you are using Android Studio, you can use the File > Settings > Project Settings > Inspections feature to manage the lint
checking to your Java or XML source files.
Configuring lint checking in Java (在.java文件中忽略lint提示的方法:用 @SuppressLint(XXX) )
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. Thelint
tool continues to check for the NewApi
issue in other methods of this class.
1 @SuppressLint("NewApi") 2 @Override 3 public void onCreate(Bundle savedInstanceState) { 4 super.onCreate(savedInstanceState); 5 setContentView(R.layout.main);
The following example shows how to turn off lint
checking for the ParserError
issue in the FeedProvider
class:
1 @SuppressLint("ParserError") 2 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 (在.xml文件中忽略lint提示,用:tools:ignore="XXX,XXX")
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.
子元素会 继承 父元素的 tools:ignore
1 <LinearLayout 2 xmlns:android="http://schemas.android.com/apk/res/android" 3 xmlns:tools="http://schemas.android.com/tools" 4 tools:ignore="UnusedResources" > 5 6 <TextView 7 android:text="@string/auto_update_prompt" /> 8 </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"