Android中apk文件里的dex文件是对java编译出来的.class文件进行重新打包,当然在打包之前会利用自己的协议做一些数据处理,例如优化函数表和变量表。在java程序中是使用classloader来加载这些编译生成的.class文件,然而在android程序中是通过DexClassLoader来装载这些文件的.这里我们就可以通过DexClassLoader在程序A里面动态装载程序B中的类,并且来调用B程序中的方法.
1.首先先建立一个普通的Android工程,在这个工程中定义一个叫做plugin的类,类中实现一个简单的方法,如下所示:
<span style="font-size:14px;">public class PluginClass {
private static String TAG = PluginClass.class.getSimpleName();
public PluginClass(){
Log.i(TAG, "initialized");
}
public void invoke(String s){
Log.i(TAG, s);
}
}</span>
2.将这个Android工程运行到安卓设备当中去3.再重新建立一个Android工程,其中定义一个叫做host的类,在这个类中实现DexClassLoader动态加载第一个工程中的plugin类,如下所示:
<span style="font-size:14px;">public class HostClass {
private static String TAG = HostClass.class.getSimpleName();
private Context mContext = null;
public HostClass(Context contect){
mContext = contect;
}
public void useDexClassLoader(){
Intent intent = new Intent();
intent.setPackage("com.example.plugin");
PackageManager pm = mContext.getPackageManager();
final List<ResolveInfo> plugins = pm.queryIntentActivities(intent,0);
if(plugins.size() <= 0){
Log.i(TAG, "resolve info size is:" + plugins.size());
return;
}
ResolveInfo resolveInfo = plugins.get(0);
ActivityInfo activityInfo = resolveInfo.activityInfo;
String div = System.getProperty("path.separator");
String packageName = activityInfo.packageName;
String dexPath = activityInfo.applicationInfo.sourceDir;
//目标类所在的apk或者jar的路径，class loader会通过这个路径来加载目标类文件
String dexOutputDir = mContext.getApplicationInfo().dataDir;
//由于dex文件是包含在apk或者jar文件中的,所以在加载class之前就需要先将dex文件解压出来，dexOutputDir为解压路径
String libPath = activityInfo.applicationInfo.nativeLibraryDir;
//目标类可能使用的c或者c++的库文件的存放路径
Log.i(TAG, "div:" + div + " " +
"packageName:" + packageName + " " +
"dexPath:" + dexPath + " " +
"dexOutputDir:" + dexOutputDir + " " +
"libPath:" + libPath);
DexClassLoader dcLoader = new DexClassLoader(dexPath,dexOutputDir,libPath,this.getClass().getClassLoader());
try {
Class<?> clazz = dcLoader.loadClass(packageName + ".PluginClass");
Object obj = clazz.newInstance();
Class[] param = new Class[1];
param[0] = String.class;
Method action = clazz.getMethod("invoke", param);
action.invoke(obj, "test this function");
} catch (ClassNotFoundException e) {
Log.i(TAG, "ClassNotFoundException");
} catch (InstantiationException e) {
Log.i(TAG, "InstantiationException");
} catch (IllegalAccessException e) {
Log.i(TAG, "IllegalAccessException");
} catch (NoSuchMethodException e) {
Log.i(TAG, "NoSuchMethodException");
} catch (IllegalArgumentException e) {
Log.i(TAG, "IllegalArgumentException");
} catch (InvocationTargetException e) {
Log.i(TAG, "InvocationTargetException");
}
}
}</span>
4.运行第二个工程之后查看log就会发现host通过DexClassLoader加载了pluginclass类,并成功调用了plugin中的方法
<span style="font-size:14px;">I/HostClass( 8341): div:: packageName:com.example.plugin dexPath:/data/app/com.example.plugin-1.apk dexOutputDir:/data/data/com.example.host libPath:/data/app-lib/com.example.plugin-1
D/dalvikvm( 8341): DexOpt: --- BEGIN 'com.example.plugin-1.apk' (bootstrap=0) ---
D/dalvikvm( 8341): DexOpt: --- END 'com.example.plugin-1.apk' (success) ---
D/dalvikvm( 8341): DEX prep '/data/app/com.example.plugin-1.apk': unzip in 39ms, rewrite 723ms
I/PluginClass( 8341): initialized
I/PluginClass( 8341): test this function
D/libEGL ( 8341): loaded /system/lib/egl/libEGL_mali.so
D/libEGL ( 8341): loaded /system/lib/egl/libGLESv1_CM_mali.so
D/libEGL ( 8341): loaded /system/lib/egl/libGLESv2_mali.so
D/OpenGLRenderer( 8341): Enabling debug mode 0
I/HostClass( 8341): div:: packageName:com.example.plugin dexPath:/data/app/com.example.plugin-1.apk dexOutputDir:/data/data/com.example.host libPath:/data/app-lib/com.example.plugin-1
I/PluginClass( 8341): initialized
I/PluginClass( 8341): test this function</span>