Android 反射调用资源和id

本文介绍利用反射调用资源和id

提出问题：

       app有一种叫应用墙的广告，应用墙是在你的程序中弹出一个Activity来展示广告，比如豌豆广点通等，集成的时候需要将资源通过复制添加到自己的项目中，但是app墙的代码是封装好的jar代码。不是源码，看不到，也不能修改。那么jar中的代码是如何加载本地资源的呢？

       自己的项目中加载资源的时候都是通过本项目的R文件来初始化资源，R文件是你自己的项目的R文件，和项目有关，如果第三方的jar文件中使用的R是来第三方SDK项目中的资源R，代码更换了项目之后铁定了是找不到你复制过来的资源的。那么这时候就需要通过特殊的方式来加载资源了，以便于调用在被集成的app中的资源。

通过原始的java反射机制的方式调用资源：

这只是一种方式，还有其他的方式。

IDHelper.java

public class IDHelper {public static int getLayout(Context mContext, String layoutName) {return ResourceHelper.getInstance(mContext).getLayoutId(layoutName);}public static int getViewID(Context mContext, String IDName) {return ResourceHelper.getInstance(mContext).getId(IDName);}public static int getDrawable(Context context, String drawableName) {return ResourceHelper.getInstance(context).getDrawableId(drawableName);}public static int getAttr(Context context, String attrName) {return ResourceHelper.getInstance(context).getAttrId(attrName);}public static int getString(Context context, String stringName) {return ResourceHelper.getInstance(context).getStringId(stringName);}}

ResourceHelper.java

public class ResourceHelper {private static ResourceHelper mResource = null;private static String mPackagename = null;private static Class<?> mLayout = null;private static Class<?> mDrawable = null;private static Class<?> mID = null;private static Class<?> mString = null;private static Class<?> mAttr = null;public static ResourceHelper getInstance(Context context) {if (mResource == null) {mPackagename = (mPackagename == null ? context.getPackageName(): mPackagename);mResource = new ResourceHelper(mPackagename);}return mResource;}public ResourceHelper(String packageName) {try {mLayout = Class.forName(packageName + ".R$layout");} catch (ClassNotFoundException e) {e.printStackTrace();}try {mDrawable = Class.forName(packageName + ".R$drawable");} catch (ClassNotFoundException e) {e.printStackTrace();}try {mID = Class.forName(packageName + ".R$id");} catch (ClassNotFoundException e) {e.printStackTrace();}try {mString = Class.forName(packageName + ".R$string");} catch (ClassNotFoundException e) {e.printStackTrace();}try {mAttr = Class.forName(packageName + ".R$attr");} catch (ClassNotFoundException e) {e.printStackTrace();}}private int getResourceId(Class<?> classType, String resourceName) {if (classType == null) {throw new IllegalArgumentException("ResClass is not initialized. Please make sure you have added neccessary resources. Also make sure you have "+ mPackagename+ ".R$* configured in obfuscation. field="+ resourceName);}try {Field field = classType.getField(resourceName);return field.getInt(resourceName);} catch (Exception e) {e.printStackTrace();Log.e("ResourceHelper","Error getting resource. Make sure you have copied all resources (res/) from SDK to your project.");}return -1;}//public int getDrawableId(String resourceName) {return getResourceId(mDrawable, resourceName);}public int getLayoutId(String resourceName) {return getResourceId(mLayout, resourceName);}public int getId(String resourceName) {return getResourceId(mID, resourceName);}public int getStringId(String resourceName) {return getResourceId(mString, resourceName);}public int getAttrId(String resourceName) {return getResourceId(mAttr, resourceName);}}

使用：

使用的时候不需要通过R来调用资源

public class MainActivity extends ActionBarActivity {private Button mButton;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(IDHelper.getLayout(getApplicationContext(),"activity_main"));//字符串是layout文件的名字initView();}private void initView() {mButton = (Button) findViewById(IDHelper.getViewID(getApplicationContext(), "button1"));mButton.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {Toast.makeText(getApplicationContext(), "HelloWorld",Toast.LENGTH_LONG).show();//字符串是控件的id}});}}

通过Android API 的通过反射获取id的方法

Context.getResources().getIdentifier("activity_main", "layout",                 paramContext.getPackageName());