layout: post title: Android通过资源文件名获取资源ID category: Android tags: Android keywords: Android，Resource，raw，drawable description: Android通过资源文件名获取资源ID
引言
当我们需要读取资源文件中一组命名有规则的资源文件时，通常我们有两种方式：
- 在res/values/arrays.xml定义一个资源数组，然后在代码中通过TypedArray去获取数组里面的资源ID；
- 在代码中申请一个资源id数据，然后将资源ID一一列出来。
上述两种方式中，第一种方式在数组比较大时，加载的时候会很耗时；第二种方式使得代码看起来很乱。本文要介绍的是另外一种方式，在代码中通过资源文件名来获取资源的ID。
实现
Resource.java提供了一个方法getIdentifier，通过这个方法可以实现资源文件名和资源ID之间的转换，该方法的详细介绍如下：
/**
* Return a resource identifier for the given resource name. A fully
* qualified resource name is of the form "package:type/entry". The first
* two components (package and type) are optional if defType and
* defPackage, respectively, are specified here.
*
* <p>Note: use of this function is discouraged. It is much more
* efficient to retrieve resources by identifier than by name.
*
* @param name The name of the desired resource.
* @param defType Optional default resource type to find, if "type/" is
* not included in the name. Can be null to require an
* explicit type.
* @param defPackage Optional default package to find, if "package:" is
* not included in the name. Can be null to require an
* explicit package.
*
* @return int The associated resource identifier. Returns 0 if no such
* resource was found. (0 is not a valid resource ID.)
*/
public int getIdentifier(String name, String defType, String defPackage) {
try {
return Integer.parseInt(name);
} catch (Exception e) {
// Ignore
}
return mAssets.getResourceIdentifier(name, defType, defPackage);
}
实际上它是引用的Asserts.java类中的getResourceIdentifier方法，这是一个native方法，具体实现被打包在库中了。
通过下面这个封装的类即可实现资源文件名到资源ID的转换，使用的时候按照注释说明传入相应地参数就可以了：
package com.uperone.resources;
import android.content.Context;
import android.text.TextUtils;
public class ResourcesUtils {
private ResourcesUtils( ){
}
/**
* use resouce name to get resource id
* @param context
* @param resourceName the resouce name that you want to get it's id
* @param type resource type,contains:
* @return -1 illegal input params, !=-1 resouce id
*
* */
public static int getResourceId( Context context, String resourcesName, String type ){
if( null == context || TextUtils.isEmpty( resourcesName ) || TextUtils.isEmpty( type ) ){
return -1;
}
return context.getResources( ).getIdentifier(resourcesName, type, context.getPackageName( ) );
}
public static final String TYPE_DRAWABLE = "drawable";
public static final String TYPE_RAW = "raw";
}