Android 中的CreatePackageContext()

2019-11-08 00:05:11

字体：大中小

来源：转载

供稿：网友

[java] view plain copy PRint?

/** * Return a new Context object for the given application name. This * Context is the same as what the named application gets when it is * launched, containing the same resources and class loader. Each call to * this method returns a new instance of a Context object; Context objects * are not shared, however they share common state (Resources, ClassLoader, * etc) so the Context instance itself is fairly lightweight. * * <p>Throws {@link PackageManager.NameNotFoundException} if there is no * application with the given package name. * * <p>Throws {@link java.lang.SecurityException} if the Context requested * can not be loaded into the caller's process for security reasons (see * {@link #CONTEXT_INCLUDE_CODE} for more information}. * * @param packageName Name of the application's package. * @param flags Option flags, one of {@link #CONTEXT_INCLUDE_CODE} * or {@link #CONTEXT_IGNORE_SECURITY}. * * @return A Context for the application. * * @throws java.lang.SecurityException * @throws PackageManager.NameNotFoundException if there is no application with * the given package name */ Override public Context createPackageContext(String packageName, int flags) throws PackageManager.NameNotFoundException { if (packageName.equals("system") || packageName.equals("android")) { final ContextImpl context = new ContextImpl(mMainThread.getSystemContext()); context.mBasePackageName = mBasePackageName; return context; } LoadedApk pi = mMainThread.getPackageInfo(packageName, mResources.getCompatibilityInfo(), flags); if (pi != null) { ContextImpl c = new ContextImpl(); c.mRestricted = (flags & CONTEXT_RESTRICTED) == CONTEXT_RESTRICTED; c.init(pi, null, mMainThread, mResources, mBasePackageName); if (c.mResources != null) { return c; } } // Should be a better exception. throw new PackageManager.NameNotFoundException( "Application package " + packageName + " not found"); } %20 %20主要作用是:创建其它程序的Context,通过创建的这个Context，就可以访问该软件包的资源，甚至可以执行其它软件包的代码。 %20 %20 %20使用： %20 [java] view%20plain copy print?

try { Context c = createPackageContext("com.dolphin.demo", Context.CONTEXT_INCLUDE_CODE | Context.CONTEXT_IGNORE_SECURITY); } catch (SecurityException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } %20 %20通常一个软件是不能创建其它程序的Context的，除非它们拥有相同的用户ID与签名。用户ID是一个字符串标识，在程序的AndroidManifest.xml文件的manifest标签中指定，格式为android:shareUserId="**"。安装在设备中的每一个apk程序，Android系统会给其分配一个单独的用户空间,其中android:shareUserId就是对应一个linux用户ID，并且为它创建一个沙箱，以防止与其它应用程序产生影响。用户ID%20在应用程序被安装到设备中时分配。通过SharedUserid,拥有同一个Userid的多个APK可以配置成运行在同一个进程中，所以默认就是可以互相访问任意数据，也可以配置成运行在不同的进程中,%20同时可以访问其APK的数据目录下的资源(图片，数据库和文件），就像访问本程序的数据一样。 %20 %20 经常的用途： %20 如经常一些应用提供的换皮肤功能，实现方法大致有两种： %20 1）把需要替换的资源图片打包好之后，放在客户端指定的目录下面，切换皮肤，查找相应的资源时，直接切换资源查找的路径到该打包文件中对应的资源路径即可。 %20 2）把需要替换的资源，放在一个空的android%20应用程序的drawable-**目录下面即可，编译，运行该apk，查找资源时，就需要用到createPackageContext获取对应包名的Context实例，然后通过context来查找对应的资源。查找时，也有两种方式： %20 2.1）通过ID来查找资源图片； %20 %20 %20 [java] view%20plain copy print?

Context context; try { context = createPackageContext("com.dolphin.demo", Context.CONTEXT_INCLUDE_CODE | Context.CONTEXT_IGNORE_SECURITY); txvA.setText(context.getResources().getText(R.string.message)); } catch (NameNotFoundException e) { e.printStackTrace(); } %20 %20 %20 %20 2.2）通过资源Name，反推出资源ID，然后查找对应的资源图片； %20 [java] view%20plain copy print?

/*** * @param clazz 目标资源的R.java * @param className R.java的内部类，如layout,string,drawable... * @param name 资源名称 * @return */ private int getResourseIdByName(Class clazz, String className, String name) { int id = 0; try { Class[] classes = clazz.getClasses(); // 获取R.java里的所有静态内部类 Class desireClass = null; for (int i = 0; i < classes.length; i++) { if (classes[i].getName().split("//$")[1].equals(className)) { desireClass = classes[i]; break; } } if (desireClass != null) id = desireClass.getField(name).getInt(desireClass); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (SecurityException e) { e.printStackTrace(); } catch (Illegal accessException e) { e.printStackTrace(); } catch (NoSuchFieldException e) { e.printStackTrace(); } return id; } Context context; try { context = createPackageContext("com.dolphin.demo", Context.CONTEXT_INCLUDE_CODE | Context.CONTEXT_IGNORE_SECURITY); Class cls = context.getClassLoader().loadClass("com.dolphin.demo.R"); // 获得目标apk的R类 txvA.setText(context.getResources().getText(getResourseIdByName(cls, "string", "message"))); } catch (NameNotFoundException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); }

上一篇：Android性能优化

下一篇：安卓获取MAC地址，适配Android 6.0