在 android 中定义常量的最佳方式是静态类、接口还是 xml 资源？

我正在开发一个 android 应用程序，它使用 Web 服务从服务器获取数据，因此我有三个不同的 URL 集来指向开发系统，测试服务器和现场服务器。无论何时我想给应用程序进行测试/活动，都很难更改 URL。所以我计划使它成为可配置的，这样应用程序就可以根据我的构建类型配置常量获得适当的 URL。 那么,

  • 这是保持这个常量、 java 静态类或 Java 公共接口或 xml 资源文件. ? < strong > 何时? 为什么？
  • 哪个性能更好? ，什么时候，为什么？

Xml 资源

<integer name="config_build_type">0</integer>
<string-array name="url_authentication">
<item >http://development.com/xxxx</item>
<item >http://test.com/xxx</item>
<item >http://example.com/xxx</item>
</string-array>

Java 静态常量

public class Config {
public static final int BUILD_TYPE = 0; // 0 - development, 1 - test, 2 - live
public static final String[] URL_AUTHENTICATION = {"http://development.com/", "http://test.com/", "http://example.com"};
}
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In general case:

  • XML values have the advantage of accessbilty in layout file and manifest file over Constants in java file
  • XML values have the advantage for multi language support over Constants in java file
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最佳答案

There is a big difference between the two in that you can reference project resources in your XML layouts. They are available in the application context and are therefore accessible across the global application. The biggest advantages of using project resources is the ease of access and that they allow you to organize your project significantly.

static final constants are compiled into the java bytecode; project resources are compiled into a binary format within the apk. Accessing either is extremely efficient... if there is a difference between the two, it is trivial at most.

There isn't a set rule on how you should be using resources/constants in your project. That said, I personally use resources for values that I might need to use in my XML or java code. On the other hand, I typically use static final constants for values that will only be used by my java code and are specific to my implementation.

Also note that it is possible to load XML resources at runtime depending on the device's current configuration (i.e. screen size, locale, etc.). So you should take this into consideration when deciding whether or not you should declare the constant in XML or directly in your .java files.

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It’s always a good practice to extract UI strings from your app code and keep them in an external file. Android makes this easy with a resources directory in each Android project.

http://developer.android.com/training/basics/supporting-devices/languages.html

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I think both way seems to be good but thing is that it depends on your requirements.

If you have your values(web service link) in your XML and suppose there is any change in your values(web service link) , you can easily change only in XML file.

But if you use inside classes as static variables you have to change in all class files.

So my suggestion is that separate constants from source file and put into resource and access it..

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Project resources need access to Context, which is not available in static methods unless you pass it in, but is always available in Activities -- there seems to be a preferential connection between resources and layouts.

For app variables and constants that may be processed in static methods I create an abstract class and do a static import (of this constants class) in all the other project class files.

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For the people who want to see how we can use a Class to define our constants and call any where we need.

Constant.java

    package org.nrum.nrum;


/**
* Created by rajdhami on 5/23/2017.
*/
public class Constant {
public static final String SERVER = "http://192.168.0.100/bs.dev/nrum";
//    public static final String SERVER = "http://192.168.100.2/bs.dev/nrum";
public static final String API_END = SERVER + "/dataProvider";
public static final String NEWS_API = API_END + "/newsApi";
public static final String BANNER_API = API_END + "/bannerApi/lists";
public static final String NOTICE_API = API_END + "/noticeApi/lists";
public static final String UPLOAD_PATH = SERVER + "/uploads";
public static final String UPLOAD_PATH_BANNER = UPLOAD_PATH + "/company_1/banner";
public static final String UPLOAD_PATH_NEWS = UPLOAD_PATH + "/company_1/news";
public static final int BANNER_TRANSITION_DURATION = 5000;
public static final int NOTICE_BUTTON_BLINK_DURATION = 5000;
public static final int BANNER_FETCH_LIMIT = 3;
}

Now we can use above constants in following way.

Constant.NOTICE_BUTTON_BLINK_DURATION
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If the constant related or depend on locale or language or use in manifest you may consider to use xml values

If the constant dont't related to translation or locale or use in manifest I would avoid to put it in xml resource

I would add enum inside the viewmodel or whatever that need to use constant as a key.

enum class Key{
key,rule,practice
}

Or

const val MY_CONST = "my constant"
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In Kotlin:

class Foo() {
// any other code for the class Foo


companion object {
const val MY_CONSTANT = "my constant"
}
}

This method is particularly recommended for data object.


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