Resources resources = context.getResources();

int indentify = resources.getIdentifier(context.getPackageName()+":drawable/"+iconName, null, null);
if(indentify>0){
icon = resources.getDrawable(indentify);
}

以下是getIdentifier的API文档，可见最重要的是第一个参数，格式是：包名 + : + 资源文件夹名 + / +资源名
如果找到了，返回资源Id，如果找不到，返回0
public int getIdentifier (String name, String defType, String defPackage)


Since: API Level 1
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.


Note: use of this function is discouraged. It is much more efficient to retrieve resources by identifier than by name.


Parameters


name The name of the desired resource.
defType Optional default resource type to find, if "type/" is not included in the name. Can be null to require an explicit type.
defPackage Optional default package to find, if "package:" is not included in the name. Can be null to require an explicit package.
Returns


int The associated resource identifier. Returns 0 if no such resource was found. (0 is not a valid resource ID.)