Android使用反射设置外部资源（SDK中使用居多）

1、在开发SDK的过程中会发现通常是以jar和资源结合。而资源是提供给外部接入方使用的，在调用的时候为了防止编译的错误，要么使用反射，要么将资源放到jar工程当前，只是最后打包的时候不打资源包，将资源外放。这里提供下使用反射在sdk中调用外部资源的方法。

2、ReflectResourcesUtil类。调用前先调用init方法，当然如果你不想调用的话我也有备用的初始化方法，使用反射获取当前应用的Application来进行初始化。

import android.app.Application;
import android.content.Context;
import android.content.res.Resources;
import android.text.TextUtils;
import android.util.Log;

import java.lang.reflect.Method;

public class ReflectResourcesUtil {
    private static final String TAG = "ReflectResourcesUtil";
    private static String mPackageName;
    private static Resources mResources;

    /**
     * 先调用初始化，然后再调用其他方法
     *
     * @param context
     */
    public static void init(Context context) {
        mPackageName = context.getApplicationContext().getPackageName();
        mResources = context.getApplicationContext().getResources();
    }

    /**
     * 防止没有调用初始化，使用备用初始化方法
     */
    private static void retryInit() {
        if (!TextUtils.isEmpty(mPackageName) || mResources != null) {
            //已经初始化过，无需要再初始化
            return;
        }
        Application application = getCurApplication();
        if (application == null)
            return;
        init(application.getApplicationContext());
    }

    public static int getLayout(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "layout", mPackageName);
    }

    public static int getDrawable(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "drawable", mPackageName);
    }

    public static int getString(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "string", mPackageName);
    }

    public static int getId(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "id", mPackageName);
    }

    public static int getStyle(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "style", mPackageName);
    }

    public static int getArray(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "array", mPackageName);
    }

    public static int getColor(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "color", mPackageName);
    }

    public static int getDimen(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "dimen", mPackageName);
    }

    public static int getAnim(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "anim", mPackageName);
    }

    public static int getRaw(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "raw", mPackageName);
    }

    public static int getStyleable(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return -1;
        }
        return mResources.getIdentifier(resName, "styleable", mPackageName);
    }

    public static int[] getStyleableArray(String resName) {
        retryInit();
        if (mResources == null || TextUtils.isEmpty(mPackageName)) {
            return null;
        }
        return getResourceIDsByName(resName, "styleable", mPackageName);
    }

    /**
     * 利用反射，获取int数组格式的资源ID，例如styleable
     */
    private static int[] getResourceIDsByName(String resName, String resType, String packageName) {
        Class clsR = null;
        int[] ids = null;
        try {
            clsR = Class.forName(packageName + ".R");
            Class[] classes = clsR.getClasses();
            Class desClass = null;
            for (int i = 0; i < classes.length; i++) {
                String[] temp = classes[i].getName().split("\\$");
                if (temp.length >= 2) {
                    if (temp[1].equals(resType)) {
                        desClass = classes[i];
                        break;
                    }
                }
            }
            if (desClass != null) {
                ids = (int[]) desClass.getField(resName).get(resName);
            }
        } catch (Exception e) {
            Log.e("ReflectResources", e.toString());
        }
        return ids;
    }

    /**
     * 获取当前应用的Application
     * 先使用ActivityThread里获取Application的方法，如果没有获取到，
     * 再使用AppGlobals里面的获取Application的方法
     *
     * @return
     */
    private static Application getCurApplication() {
        Application application = null;
        try {
            Class atClass = Class.forName("android.app.ActivityThread");
            Method currentApplicationMethod = atClass.getDeclaredMethod("currentApplication");
            currentApplicationMethod.setAccessible(true);
            application = (Application) currentApplicationMethod.invoke(null);
            Log.d(TAG, "curApp class1:" + application);
        } catch (Exception e) {
            Log.d(TAG, "e:" + e.toString());
        }

        if (application != null)
            return application;

        try {
            Class atClass = Class.forName("android.app.AppGlobals");
            Method currentApplicationMethod = atClass.getDeclaredMethod("getInitialApplication");
            currentApplicationMethod.setAccessible(true);
            application = (Application) currentApplicationMethod.invoke(null);
            Log.d(TAG, "curApp class2:" + application);
        } catch (Exception e) {
            Log.d(TAG, "e:" + e.toString());
        }

        return application;
    }
}