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);
	}

}

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);
	}

}

使用的时候不需要通过R来调用资源

public class MainActivity extends ActionBarActivity {
	private Button mButton;

	@Override
	protected 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() {

			@Override
			public void onClick(View arg0) {
				Toast.makeText(getApplicationContext(), "HelloWorld",
						Toast.LENGTH_LONG).show();//字符串是控件的id
			}
		});
	}
}

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

Android 反射调用资源和id