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Android根据资源名获取资源ID

接触过Android开发的同学们都知道在Android中访问程序资源基本都是通过资源ID来访问。这样开发起来很简单,并且可以不去考虑各种分辨率,语言等不同资源显式指定。

痛点

但是,有时候也会有一些问题,比如我们根据服务器端的值取图片,但是服务器端绝对不会返回给我们的是资源id,最多是一种和文件名相关联的值,操作资源少的时候,可以维护一个容器进行值与资源ID的映射,但是多的话,就需要另想办法了。

便捷的方法

在这种情况下,使用文件名来得到资源ID显得事半功倍。 通过调用Resources的getIdentifier可以很轻松地得到资源ID。 几个简单的示例

lineos:false
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Resources res = getResources();
final String packageName = getPackageName();
int imageResId = res.getIdentifier("ic_launcher", "drawable", packageName);
int imageResIdByAnotherForm = res.getIdentifier(packageName + ":drawable/ic_launcher", null, null);
  
int musicResId = res.getIdentifier("test", "raw", packageName);
      
int notFoundResId = res.getIdentifier("activity_main", "drawable", packageName);

Log.i(LOGTAG, "testGetResourceIds imageResId = " + imageResId
              + ";imageResIdByAnotherForm = " + imageResIdByAnotherForm
              + ";musicResId=" + musicResId
              + ";notFoundResId =" + notFoundResId);

运行结果

lineos:false
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I/MainActivity( 4537): testGetResourceIds imageResId = 2130837504;imageResIdByAnotherForm = 2130837504;musicResId=2130968576;notFoundResId =0

看一看API

直接API

  • 这个方法用来使用资源名来获取资源ID
  • 完整的资源名为package:type/entry,如果资源名这个参数有完整地指定,后面的defType和defPackage可以省略。
  • defType和defPackage省略时,需要将其设置成null
  • 注意这个方法不提倡,因为直接通过资源ID访问资源会更加效率高
  • 如果资源没有找到,返回0,在Android资源ID中0不是合法的资源ID。
lineos:false android.content.res.Resources.class
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/**
     * 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);
    }

间接API

实际上上述API调用的是AssetManager.class中的native方法。

lineos:false
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/**
     * Retrieve the resource identifier for the given resource name.
     */
    /*package*/ native final int getResourceIdentifier(String type,
                                                       String name,
                                                       String defPackage);

其他


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