Instant Run

Instant Run，是android studio2.0新增的一个运行机制，在你编码开发、测试或debug的时候，它都能显著减少你对当前应用的构建和部署的时间。通俗的解释就是，当你在Android Studio中改了你的代码，Instant Run可以很快的让你看到你修改的效果。而在没有Instant Run之前，你的一个小小的修改，都肯能需要几十秒甚至更长的等待才能看到修改后的效果。

传统的代码修改及编译部署流程

传统的代码修改及编译流程如下：构建整个apk → 部署app → app重启 → 重启Activity

Instant Run编译和部署流程

Instant Run构建项目的流程：构建修改的部分 → 部署修改的dex或资源 → 热部署，温部署，冷部署

热拔插，温拔插，冷拔插

热拔插：代码改变被应用、投射到APP上，不需要重启应用，不需要重建当前activity。
场景：适用于多数的简单改变（包括一些方法实现的修改，或者变量值修改）
**温拔插：**activity需要被重启才能看到所需更改。
场景：典型的情况是代码修改涉及到了资源文件，即resources。
**冷拔插：**app需要被重启（但是仍然不需要重新安装）
场景：任何涉及结构性变化的，比如：修改了继承规则、修改了方法签名等。

首次运行Instant Run，Gradle执行过程

一个新的App Server类会被注入到App中，与Bytecode instrumentation协同监控代码的变化。
同时会有一个新的Application类，它注入了一个自定义类加载器（Class Loader）,同时该Application类会启动我们所需的新注入的App Server。于是，Manifest会被修改来确保我们的应用能使用这个新的Application类。（这里不必担心自己继承定义了Application类，Instant Run添加的这个新Application类会代理我们自定义的Application类）
至此，Instant Run已经可以跑起来了，在我们使用的时候，它会通过决策，合理运用冷温热拔插来协助我们大量地缩短构建程序的时间。

在Instant Run运行之前，Android Studio会检查是否能连接到App Server中。并且确保这个App Server是Android Studio所需要的。这同样能确保该应用正处在前台。

热拔插

Android Studio monitors： 运行着Gradle任务来生成增量.dex文件（这个dex文件是对应着开发中的修改类） Android Studio会提取这些.dex文件发送到App Server，然后部署到App（Gradle修改class的原理，请戳链接）。

App Server会不断监听是否需要重写类文件，如果需要，任务会被立马执行。新的更改便能立即被响应。我们可以通过打断点的方式来查看。

温拔插

温拔插需要重启Activity，因为资源文件是在Activity创建时加载，所以必须重启Activity来重载资源文件。
目前来说，任何资源文件的修改都会导致重新打包再发送到APP。但是，google的开发团队正在致力于开发一个增量包，这个增量包只会包装修改过的资源文件并能部署到当前APP上。
所以温拔插实际上只能应对少数的情况，它并不能应付应用在架构、结构上的变化。

注：温拔插涉及到的资源文件修改，在manifest上是无效的（这里的无效是指不会启动Instant Run），因为，manifest的值是在APK安装的时候被读取，所以想要manifest下资源的修改生效，还需要触发一个完整的应用构建和部署。

冷拔插

应用部署的时候，会把工程拆分成十个部分，每部分都拥有自己的.dex文件，然后所有的类会根据包名被分配给相应的.dex文件。当冷拔插开启时，修改过的类所对应的.dex文件，会重组生成新的.dex文件，然后再部署到设备上。
之所以能这么做，是依赖于Android的ART模式，它能允许加载多个.dex文件。ART模式在android4.4（API-19）中加入，但是Dalvik依然是首选，到了android5.0（API-21），ART模式才成为系统默认首选，所以Instant Run只能运行在API-21及其以上版本。

使用Instant Run一些注意点

Instant Run是被Android Studio控制的。所以我们只能通过IDE来启动它，如果通过设备来启动应用，Instant Run会出现异常情况。在使用Instant Run来启动Android app的时候，应注意以下几点：

1. 如果应用的minSdkVersion小于21，可能多数的Instant Run功能会挂掉，这里提供一个解决方法，通过product flavor建立一个minSdkVersion大于21的新分支，用来debug。
2. Instant Run目前只能在主进程里运行，如果应用是多进程的，类似微信，把webView抽出来单独一个进程，那热、温拔插会被降级为冷拔插。
3. 在Windows下，Windows Defender Real-Time Protection可能会导致Instant Run挂掉，可用通过添加白名单列表解决。
4. 暂时不支持Jack compiler，Instrumentation Tests，或者同时部署到多台设备。

结合Demo深度理解

为了方便大家的理解，我们新建一个项目，里面不写任何的逻辑功能，只对application做一个修改：

首先，我们先反编译一下APK的构成，使用的工具：d2j-dex2jar 和jd-gui。

我们要看的启动的信息就在这个instant-run.zip文件里面，解压instant-run.zip，我们会发现，我们真正的业务代码都在这里。

从instant-run文件中我们猜想是BootstrapApplication替换了我们的application，Instant-Run代码作为一个宿主程序，将app作为资源dex加载起来。

那么InstantRun是怎么把业务代码运行起来的呢？

Instant Run如何启动app

按照我们上面对instant-run运行机制的猜想，我们首先看一下appliaction的分析attachBaseContext和onCreate方法。

attachBaseContext()

protected void attachBaseContext(Context context) { 
if (!AppInfo.usingApkSplits) { 
String apkFile = context.getApplicationInfo().sourceDir; 
long apkModified = apkFile != null ? new File(apkFile) 
.lastModified() : 0L; 
createResources(apkModified); 
setupClassLoaders(context, context.getCacheDir().getPath(), 
apkModified); 
} 
createRealApplication(); 
super.attachBaseContext(context); 
if (this.realApplication != null) { 
try { 
Method attachBaseContext = ContextWrapper.class 
.getDeclaredMethod("attachBaseContext", 
new Class[] { Context.class }); 
attachBaseContext.setAccessible(true); 
attachBaseContext.invoke(this.realApplication, 
new Object[] { context }); 
} catch (Exception e) { 
throw new IllegalStateException(e); 
} 
} 
}

我们依次需要关注的方法有：
createResources → setupClassLoaders → createRealApplication → 调用realApplication的attachBaseContext方法

createResources()

private void createResources(long apkModified) { 
FileManager.checkInbox(); 
File file = FileManager.getExternalResourceFile(); 
this.externalResourcePath = (file != null ? file.getPath() : null); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Resource override is " 
+ this.externalResourcePath); 
} 
if (file != null) { 
try { 
long resourceModified = file.lastModified(); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Resource patch last modified: " 
+ resourceModified); 
Log.v("InstantRun", "APK last modified: " + apkModified 
+ " " 
+ (apkModified > resourceModified ? ">" : "<") 
+ " resource patch"); 
} 
if ((apkModified == 0L) || (resourceModified <= apkModified)) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Ignoring resource file, older than APK"); 
} 
this.externalResourcePath = null; 
} 
} catch (Throwable t) { 
Log.e("InstantRun", "Failed to check patch timestamps", t); 
} 
} 
}

说明：该方法主要是判断资源resource.ap_是否改变，然后保存resource.ap_的路径到externalResourcePath中。

setupClassLoaders()

private static void setupClassLoaders(Context context, String codeCacheDir, 
long apkModified) { 
List dexList = FileManager.getDexList(context, apkModified); 
Class server = Server.class; 
Class patcher = MonkeyPatcher.class; 
if (!dexList.isEmpty()) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Bootstrapping class loader with dex list " 
+ join('/n', dexList)); 
} 
ClassLoader classLoader = BootstrapApplication.class 
.getClassLoader(); 
String nativeLibraryPath; 
try { 
nativeLibraryPath = (String) classLoader.getClass() 
.getMethod("getLdLibraryPath", new Class[0]) 
.invoke(classLoader, new Object[0]); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Native library path: " 
+ nativeLibraryPath); 
} 
} catch (Throwable t) { 
Log.e("InstantRun", "Failed to determine native library path " 
+ t.getMessage()); 
nativeLibraryPath = FileManager.getNativeLibraryFolder() 
.getPath(); 
} 
IncrementalClassLoader.inject(classLoader, nativeLibraryPath, 
codeCacheDir, dexList); 
} 
}

说明，该方法是初始化一个ClassLoaders并调用IncrementalClassLoader。
IncrementalClassLoader的源码如下：

public class IncrementalClassLoader extends ClassLoader { 
public static final boolean DEBUG_CLASS_LOADING = false; 
private final DelegateClassLoader delegateClassLoader; 
public IncrementalClassLoader(ClassLoader original, 
String nativeLibraryPath, String codeCacheDir, List dexes) { 
super(original.getParent()); 
this.delegateClassLoader = createDelegateClassLoader(nativeLibraryPath, 
codeCacheDir, dexes, original); 
} 
public Class findClass(String className) throws ClassNotFoundException { 
try { 
return this.delegateClassLoader.findClass(className); 
} catch (ClassNotFoundException e) { 
throw e; 
} 
} 
private static class DelegateClassLoader extends BaseDexClassLoader { 
private DelegateClassLoader(String dexPath, File optimizedDirectory, 
String libraryPath, ClassLoader parent) { 
super(dexPath, optimizedDirectory, libraryPath, parent); 
} 
public Class findClass(String name) throws ClassNotFoundException { 
try { 
return super.findClass(name); 
} catch (ClassNotFoundException e) { 
throw e; 
} 
} 
} 
private static DelegateClassLoader createDelegateClassLoader( 
String nativeLibraryPath, String codeCacheDir, List dexes, 
ClassLoader original) { 
String pathBuilder = createDexPath(dexes); 
return new DelegateClassLoader(pathBuilder, new File(codeCacheDir), 
nativeLibraryPath, original); 
} 
private static String createDexPath(List dexes) { 
StringBuilder pathBuilder = new StringBuilder(); 
boolean first = true; 
for (String dex : dexes) { 
if (first) { 
first = false; 
} else { 
pathBuilder.append(File.pathSeparator); 
} 
pathBuilder.append(dex); 
} 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Incremental dex path is " 
+ BootstrapApplication.join('/n', dexes)); 
} 
return pathBuilder.toString(); 
} 
private static void setParent(ClassLoader classLoader, ClassLoader newParent) { 
try { 
Field parent = ClassLoader.class.getDeclaredField("parent"); 
parent.setAccessible(true); 
parent.set(classLoader, newParent); 
} catch (IllegalArgumentException e) { 
throw new RuntimeException(e); 
} catch (IllegalAccessException e) { 
throw new RuntimeException(e); 
} catch (NoSuchFieldException e) { 
throw new RuntimeException(e); 
} 
} 
public static ClassLoader inject(ClassLoader classLoader, 
String nativeLibraryPath, String codeCacheDir, List dexes) { 
IncrementalClassLoader incrementalClassLoader = new IncrementalClassLoader( 
classLoader, nativeLibraryPath, codeCacheDir, dexes); 
setParent(classLoader, incrementalClassLoader); 
return incrementalClassLoader; 
} 
}

inject方法是用来设置classloader的父子顺序的，使用IncrementalClassLoader来加载dex。由于ClassLoader的双亲委托模式，也就是委托父类加载类，父类中找不到再在本ClassLoader中查找。
调用的效果图如下：

为了方便我们对委托父类加载机制的理解，我们可以做一个实验，在我们的application做一些Log。

@Override 
public void onCreate() { 
super.onCreate(); 
try{ 
Log.d(TAG,"###onCreate in myApplication"); 
String classLoaderName = getClassLoader().getClass().getName(); 
Log.d(TAG,"###onCreate in myApplication classLoaderName = "+classLoaderName); 
String parentClassLoaderName = getClassLoader().getParent().getClass().getName(); 
Log.d(TAG,"###onCreate in myApplication parentClassLoaderName = "+parentClassLoaderName); 
String pParentClassLoaderName = getClassLoader().getParent().getParent().getClass().getName(); 
Log.d(TAG,"###onCreate in myApplication pParentClassLoaderName = "+pParentClassLoaderName); 
}catch (Exception e){ 
e.printStackTrace(); 
} 
}

输出结果：

03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication classLoaderName = dalvik.system.PathClassLoader 
03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication parentClassLoaderName = com.android.tools.fd.runtime.IncrementalClassLoader 
03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication pParentClassLoaderName = java.lang.BootClassLoader

由此，我们知道，当前PathClassLoader委托IncrementalClassLoader加载dex。

我们继续对attachBaseContext()继续分析：

attachBaseContext.invoke(this.realApplication, 
new Object[] { context });

createRealApplication

private void createRealApplication() { 
if (AppInfo.applicationClass != null) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"About to create real application of class name = " 
+ AppInfo.applicationClass); 
} 
try { 
Class realClass = (Class) Class 
.forName(AppInfo.applicationClass); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Created delegate app class successfully : " 
+ realClass + " with class loader " 
+ realClass.getClassLoader()); 
} 
Constructor constructor = realClass 
.getConstructor(new Class[0]); 
this.realApplication = ((Application) constructor 
.newInstance(new Object[0])); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Created real app instance successfully :" 
+ this.realApplication); 
} 
} catch (Exception e) { 
throw new IllegalStateException(e); 
} 
} else { 
this.realApplication = new Application(); 
} 
}

该方法就是用classes.dex中的AppInfo类的applicationClass常量中保存的app真实的application。由例子的分析我们可以知道applicationClass就是com.xzh.demo.MyApplication。通过反射的方式，创建真是的realApplication。
看完attachBaseContext我们继续看BootstrapApplication();

BootstrapApplication()

我们首先看一下onCreate方法：

onCreate()

public void onCreate() { 
if (!AppInfo.usingApkSplits) { 
MonkeyPatcher.monkeyPatchApplication(this, this, 
this.realApplication, this.externalResourcePath); 
MonkeyPatcher.monkeyPatchExistingResources(this, 
this.externalResourcePath, null); 
} else { 
MonkeyPatcher.monkeyPatchApplication(this, this, 
this.realApplication, null); 
} 
super.onCreate(); 
if (AppInfo.applicationId != null) { 
try { 
boolean foundPackage = false; 
int pid = Process.myPid(); 
ActivityManager manager = (ActivityManager) getSystemService("activity"); 
List processes = manager 
.getRunningAppProcesses(); 
boolean startServer = false; 
if ((processes != null) && (processes.size() > 1)) { 
for (ActivityManager.RunningAppProcessInfo processInfo : processes) { 
if (AppInfo.applicationId 
.equals(processInfo.processName)) { 
foundPackage = true; 
if (processInfo.pid == pid) { 
startServer = true; 
break; 
} 
} 
} 
if ((!startServer) && (!foundPackage)) { 
startServer = true; 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Multiprocess but didn't find process with package: starting server anyway"); 
} 
} 
} else { 
startServer = true; 
} 
if (startServer) { 
Server.create(AppInfo.applicationId, this); 
} 
} catch (Throwable t) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Failed during multi process check", t); 
} 
Server.create(AppInfo.applicationId, this); 
} 
} 
if (this.realApplication != null) { 
this.realApplication.onCreate(); 
} 
}

在onCreate()中我们需要注意以下方法：
monkeyPatchApplication → monkeyPatchExistingResources → Server启动 → 调用realApplication的onCreate方法

monkeyPatchApplication

public static void monkeyPatchApplication(Context context, 
Application bootstrap, Application realApplication, 
String externalResourceFile) { 
try { 
Class activityThread = Class 
.forName("android.app.ActivityThread"); 
Object currentActivityThread = getActivityThread(context, 
activityThread); 
Field mInitialApplication = activityThread 
.getDeclaredField("mInitialApplication"); 
mInitialApplication.setAccessible(true); 
Application initialApplication = (Application) mInitialApplication 
.get(currentActivityThread); 
if ((realApplication != null) && (initialApplication == bootstrap)) { 
mInitialApplication.set(currentActivityThread, realApplication); 
} 
if (realApplication != null) { 
Field mAllApplications = activityThread 
.getDeclaredField("mAllApplications"); 
mAllApplications.setAccessible(true); 
List allApplications = (List) mAllApplications 
.get(currentActivityThread); 
for (int i = 0; i < allApplications.size(); i++) { 
if (allApplications.get(i) == bootstrap) { 
allApplications.set(i, realApplication); 
} 
} 
} 
Class loadedApkClass; 
try { 
loadedApkClass = Class.forName("android.app.LoadedApk"); 
} catch (ClassNotFoundException e) { 
loadedApkClass = Class 
.forName("android.app.ActivityThread$PackageInfo"); 
} 
Field mApplication = loadedApkClass 
.getDeclaredField("mApplication"); 
mApplication.setAccessible(true); 
Field mResDir = loadedApkClass.getDeclaredField("mResDir"); 
mResDir.setAccessible(true); 
Field mLoadedApk = null; 
try { 
mLoadedApk = Application.class.getDeclaredField("mLoadedApk"); 
} catch (NoSuchFieldException e) { 
} 
for (String fieldName : new String[] { "mPackages", 
"mResourcePackages" }) { 
Field field = activityThread.getDeclaredField(fieldName); 
field.setAccessible(true); 
Object value = field.get(currentActivityThread); 
for (Map.Entry> entry : ((Map>) value) 
.entrySet()) { 
Object loadedApk = ((WeakReference) entry.getValue()).get(); 
if (loadedApk != null) { 
if (mApplication.get(loadedApk) == bootstrap) { 
if (realApplication != null) { 
mApplication.set(loadedApk, realApplication); 
} 
if (externalResourceFile != null) { 
mResDir.set(loadedApk, externalResourceFile); 
} 
if ((realApplication != null) 
&& (mLoadedApk != null)) { 
mLoadedApk.set(realApplication, loadedApk); 
} 
} 
} 
} 
} 
} catch (Throwable e) { 
throw new IllegalStateException(e); 
} 
}

说明：该方法的作用是替换所有当前app的application为realApplication。
替换的过程如下：
1.替换ActivityThread的mInitialApplication为realApplication
2.替换mAllApplications 中所有的Application为realApplication
3.替换ActivityThread的mPackages,mResourcePackages中的mLoaderApk中的application为realApplication。

monkeyPatchExistingResources

public static void monkeyPatchExistingResources(Context context, 
String externalResourceFile, Collection activities) { 
if (externalResourceFile == null) { 
return; 
} 
try { 
AssetManager newAssetManager = (AssetManager) AssetManager.class 
.getConstructor(new Class[0]).newInstance(new Object[0]); 
Method mAddAssetPath = AssetManager.class.getDeclaredMethod( 
"addAssetPath", new Class[] { String.class }); 
mAddAssetPath.setAccessible(true); 
if (((Integer) mAddAssetPath.invoke(newAssetManager, 
new Object[] { externalResourceFile })).intValue() == 0) { 
throw new IllegalStateException( 
"Could not create new AssetManager"); 
} 
Method mEnsureStringBlocks = AssetManager.class.getDeclaredMethod( 
"ensureStringBlocks", new Class[0]); 
mEnsureStringBlocks.setAccessible(true); 
mEnsureStringBlocks.invoke(newAssetManager, new Object[0]); 
if (activities != null) { 
for (Activity activity : activities) { 
Resources resources = activity.getResources(); 
try { 
Field mAssets = Resources.class 
.getDeclaredField("mAssets"); 
mAssets.setAccessible(true); 
mAssets.set(resources, newAssetManager); 
} catch (Throwable ignore) { 
Field mResourcesImpl = Resources.class 
.getDeclaredField("mResourcesImpl"); 
mResourcesImpl.setAccessible(true); 
Object resourceImpl = mResourcesImpl.get(resources); 
Field implAssets = resourceImpl.getClass() 
.getDeclaredField("mAssets"); 
implAssets.setAccessible(true); 
implAssets.set(resourceImpl, newAssetManager); 
} 
Resources.Theme theme = activity.getTheme(); 
try { 
try { 
Field ma = Resources.Theme.class 
.getDeclaredField("mAssets"); 
ma.setAccessible(true); 
ma.set(theme, newAssetManager); 
} catch (NoSuchFieldException ignore) { 
Field themeField = Resources.Theme.class 
.getDeclaredField("mThemeImpl"); 
themeField.setAccessible(true); 
Object impl = themeField.get(theme); 
Field ma = impl.getClass().getDeclaredField( 
"mAssets"); 
ma.setAccessible(true); 
ma.set(impl, newAssetManager); 
} 
Field mt = ContextThemeWrapper.class 
.getDeclaredField("mTheme"); 
mt.setAccessible(true); 
mt.set(activity, null); 
Method mtm = ContextThemeWrapper.class 
.getDeclaredMethod("initializeTheme", 
new Class[0]); 
mtm.setAccessible(true); 
mtm.invoke(activity, new Object[0]); 
Method mCreateTheme = AssetManager.class 
.getDeclaredMethod("createTheme", new Class[0]); 
mCreateTheme.setAccessible(true); 
Object internalTheme = mCreateTheme.invoke( 
newAssetManager, new Object[0]); 
Field mTheme = Resources.Theme.class 
.getDeclaredField("mTheme"); 
mTheme.setAccessible(true); 
mTheme.set(theme, internalTheme); 
} catch (Throwable e) { 
Log.e("InstantRun", 
"Failed to update existing theme for activity " 
+ activity, e); 
} 
pruneResourceCaches(resources); 
} 
} 
Collection> references; 
if (Build.VERSION.SDK_INT >= 19) { 
Class resourcesManagerClass = Class 
.forName("android.app.ResourcesManager"); 
Method mGetInstance = resourcesManagerClass.getDeclaredMethod( 
"getInstance", new Class[0]); 
mGetInstance.setAccessible(true); 
Object resourcesManager = mGetInstance.invoke(null, 
new Object[0]); 
try { 
Field fMActiveResources = resourcesManagerClass 
.getDeclaredField("mActiveResources"); 
fMActiveResources.setAccessible(true); 
ArrayMap> arrayMap = (ArrayMap) fMActiveResources 
.get(resourcesManager); 
references = arrayMap.values(); 
} catch (NoSuchFieldException ignore) { 
Field mResourceReferences = resourcesManagerClass 
.getDeclaredField("mResourceReferences"); 
mResourceReferences.setAccessible(true); 
references = (Collection) mResourceReferences 
.get(resourcesManager); 
} 
} else { 
Class activityThread = Class 
.forName("android.app.ActivityThread"); 
Field fMActiveResources = activityThread 
.getDeclaredField("mActiveResources"); 
fMActiveResources.setAccessible(true); 
Object thread = getActivityThread(context, activityThread); 
HashMap> map = (HashMap) fMActiveResources 
.get(thread); 
references = map.values(); 
} 
for (WeakReference wr : references) { 
Resources resources = (Resources) wr.get(); 
if (resources != null) { 
try { 
Field mAssets = Resources.class 
.getDeclaredField("mAssets"); 
mAssets.setAccessible(true); 
mAssets.set(resources, newAssetManager); 
} catch (Throwable ignore) { 
Field mResourcesImpl = Resources.class 
.getDeclaredField("mResourcesImpl"); 
mResourcesImpl.setAccessible(true); 
Object resourceImpl = mResourcesImpl.get(resources); 
Field implAssets = resourceImpl.getClass() 
.getDeclaredField("mAssets"); 
implAssets.setAccessible(true); 
implAssets.set(resourceImpl, newAssetManager); 
} 
resources.updateConfiguration(resources.getConfiguration(), 
resources.getDisplayMetrics()); 
} 
} 
} catch (Throwable e) { 
throw new IllegalStateException(e); 
} 
}

说明：该方法的作用是替换所有当前app的mAssets为newAssetManager。
monkeyPatchExistingResources的流程如下：
1.如果resource.ap_文件有改变，那么新建一个AssetManager对象newAssetManager，然后用newAssetManager对象替换所有当前Resource、Resource.Theme的mAssets成员变量。
2.如果当前的已经有Activity启动了，还需要替换所有Activity中mAssets成员变量

判断Server是否已经启动，如果没有启动，则启动Server。然后调用realApplication的onCreate方法代理realApplication的生命周期。

接下来我们分析下Server负责的热部署、温部署和冷部署等问题。

Server热部署、温部署和冷部署

首先重点关注一下Server的内部类SocketServerReplyThread。

SocketServerReplyThread

private class SocketServerReplyThread extends Thread { 
private final LocalSocket mSocket; 
SocketServerReplyThread(LocalSocket socket) { 
this.mSocket = socket; 
} 
public void run() { 
try { 
DataInputStream input = new DataInputStream( 
this.mSocket.getInputStream()); 
DataOutputStream output = new DataOutputStream( 
this.mSocket.getOutputStream()); 
try { 
handle(input, output); 
} finally { 
try { 
input.close(); 
} catch (IOException ignore) { 
} 
try { 
output.close(); 
} catch (IOException ignore) { 
} 
} 
return; 
} catch (IOException e) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Fatal error receiving messages", e); 
} 
} 
} 
private void handle(DataInputStream input, DataOutputStream output) 
throws IOException { 
long magic = input.readLong(); 
if (magic != 890269988L) { 
Log.w("InstantRun", 
"Unrecognized header format " + Long.toHexString(magic)); 
return; 
} 
int version = input.readInt(); 
output.writeInt(4); 
if (version != 4) { 
Log.w("InstantRun", 
"Mismatched protocol versions; app is using version 4 and tool is using version " 
+ version); 
} else { 
int message; 
for (;;) { 
message = input.readInt(); 
switch (message) { 
case 7: 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Received EOF from the IDE"); 
} 
return; 
case 2: 
boolean active = Restarter 
.getForegroundActivity(Server.this.mApplication) != null; 
output.writeBoolean(active); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Received Ping message from the IDE; returned active = " 
+ active); 
} 
break; 
case 3: 
String path = input.readUTF(); 
long size = FileManager.getFileSize(path); 
output.writeLong(size); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Received path-exists(" + path 
+ ") from the " + "IDE; returned size=" 
+ size); 
} 
break; 
case 4: 
long begin = System.currentTimeMillis(); 
path = input.readUTF(); 
byte[] checksum = FileManager.getCheckSum(path); 
if (checksum != null) { 
output.writeInt(checksum.length); 
output.write(checksum); 
if (Log.isLoggable("InstantRun", 2)) { 
long end = System.currentTimeMillis(); 
String hash = new BigInteger(1, checksum) 
.toString(16); 
Log.v("InstantRun", "Received checksum(" + path 
+ ") from the " + "IDE: took " 
+ (end - begin) + "ms to compute " 
+ hash); 
} 
} else { 
output.writeInt(0); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Received checksum(" + path 
+ ") from the " 
+ "IDE: returning "); 
} 
} 
break; 
case 5: 
if (!authenticate(input)) { 
return; 
} 
Activity activity = Restarter 
.getForegroundActivity(Server.this.mApplication); 
if (activity != null) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Restarting activity per user request"); 
} 
Restarter.restartActivityOnUiThread(activity); 
} 
break; 
case 1: 
if (!authenticate(input)) { 
return; 
} 
List changes = ApplicationPatch 
.read(input); 
if (changes != null) { 
boolean hasResources = Server.hasResources(changes); 
int updateMode = input.readInt(); 
updateMode = Server.this.handlePatches(changes, 
hasResources, updateMode); 
boolean showToast = input.readBoolean(); 
output.writeBoolean(true); 
Server.this.restart(updateMode, hasResources, 
showToast); 
} 
break; 
case 6: 
String text = input.readUTF(); 
Activity foreground = Restarter 
.getForegroundActivity(Server.this.mApplication); 
if (foreground != null) { 
Restarter.showToast(foreground, text); 
} else if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", 
"Couldn't show toast (no activity) : " 
+ text); 
} 
break; 
} 
} 
} 
} 
}

说明：socket开启后，开始读取数据，当读到1时，获取代码变化的ApplicationPatch列表，然后调用handlePatches来处理代码的变化。

handlePatches

private int handlePatches(List changes, 
boolean hasResources, int updateMode) { 
if (hasResources) { 
FileManager.startUpdate(); 
} 
for (ApplicationPatch change : changes) { 
String path = change.getPath(); 
if (path.endsWith(".dex")) { 
handleColdSwapPatch(change); 
boolean canHotSwap = false; 
for (ApplicationPatch c : changes) { 
if (c.getPath().equals("classes.dex.3")) { 
canHotSwap = true; 
break; 
} 
} 
if (!canHotSwap) { 
updateMode = 3; 
} 
} else if (path.equals("classes.dex.3")) { 
updateMode = handleHotSwapPatch(updateMode, change); 
} else if (isResourcePath(path)) { 
updateMode = handleResourcePatch(updateMode, change, path); 
} 
} 
if (hasResources) { 
FileManager.finishUpdate(true); 
} 
return updateMode; 
}

说明：本方法主要通过判断Change的内容，来判断采用什么模式（热部署、温部署或冷部署）

• 如果后缀为“.dex”,冷部署处理handleColdSwapPatch
• 如果后缀为“classes.dex.3”,热部署处理handleHotSwapPatch
• 其他情况,温部署，处理资源handleResourcePatch

handleColdSwapPatch冷部署

private static void handleColdSwapPatch(ApplicationPatch patch) { 
if (patch.path.startsWith("slice-")) { 
File file = FileManager.writeDexShard(patch.getBytes(), patch.path); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Received dex shard " + file); 
} 
} 
}

说明：该方法把dex文件写到私有目录，等待整个app重启，重启之后，使用前面提到的IncrementalClassLoader加载dex即可。

handleHotSwapPatch热部署

private int handleHotSwapPatch(int updateMode, ApplicationPatch patch) { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Received incremental code patch"); 
} 
try { 
String dexFile = FileManager.writeTempDexFile(patch.getBytes()); 
if (dexFile == null) { 
Log.e("InstantRun", "No file to write the code to"); 
return updateMode; 
} 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Reading live code from " + dexFile); 
} 
String nativeLibraryPath = FileManager.getNativeLibraryFolder() 
.getPath(); 
DexClassLoader dexClassLoader = new DexClassLoader(dexFile, 
this.mApplication.getCacheDir().getPath(), 
nativeLibraryPath, getClass().getClassLoader()); 
Class aClass = Class.forName( 
"com.android.tools.fd.runtime.AppPatchesLoaderImpl", true, 
dexClassLoader); 
try { 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Got the patcher class " + aClass); 
} 
PatchesLoader loader = (PatchesLoader) aClass.newInstance(); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Got the patcher instance " + loader); 
} 
String[] getPatchedClasses = (String[]) aClass 
.getDeclaredMethod("getPatchedClasses", new Class[0]) 
.invoke(loader, new Object[0]); 
if (Log.isLoggable("InstantRun", 2)) { 
Log.v("InstantRun", "Got the list of classes "); 
for (String getPatchedClass : getPatchedClasses) { 
Log.v("InstantRun", "class " + getPatchedClass); 
} 
} 
if (!loader.load()) { 
updateMode = 3; 
} 
} catch (Exception e) { 
Log.e("InstantRun", "Couldn't apply code changes", e); 
e.printStackTrace(); 
updateMode = 3; 
} 
} catch (Throwable e) { 
Log.e("InstantRun", "Couldn't apply code changes", e); 
updateMode = 3; 
} 
return updateMode; 
}

说明：该方法将patch的dex文件写入到临时目录，然后使用DexClassLoader去加载dex。然后反射调用AppPatchesLoaderImpl类的load方法。
需要强调的是：AppPatchesLoaderImpl继承自抽象类AbstractPatchesLoaderImpl，并实现了抽象方法：getPatchedClasses。而AbstractPatchesLoaderImpl抽象类代码如下：

public abstract class AbstractPatchesLoaderImpl implements PatchesLoader { 
public abstract String[] getPatchedClasses(); 
public boolean load() { 
try { 
for (String className : getPatchedClasses()) { 
ClassLoader cl = getClass().getClassLoader(); 
Class aClass = cl.loadClass(className + "$override"); 
Object o = aClass.newInstance(); 
Class originalClass = cl.loadClass(className); 
Field changeField = originalClass.getDeclaredField("$change"); 
changeField.setAccessible(true); 
Object previous = changeField.get(null); 
if (previous != null) { 
Field isObsolete = previous.getClass().getDeclaredField( 
"$obsolete"); 
if (isObsolete != null) { 
isObsolete.set(null, Boolean.valueOf(true)); 
} 
} 
changeField.set(null, o); 
if ((Log.logging != null) 
&& (Log.logging.isLoggable(Level.FINE))) { 
Log.logging.log(Level.FINE, String.format("patched %s", 
new Object[] { className })); 
} 
} 
} catch (Exception e) { 
if (Log.logging != null) { 
Log.logging.log(Level.SEVERE, String.format( 
"Exception while patching %s", 
new Object[] { "foo.bar" }), e); 
} 
return false; 
} 
return true; 
} 
}

Instant Run热部署原理

由上面的代码分析，我们对Instant Run的流程可以分析如下：

1，在第一次构建apk时，在每一个类中注入了一个$change的成员变量，它实现了IncrementalChange接口，并在每一个方法中，插入了一段类似的逻辑。

IncrementalChange localIncrementalChange = $change; 
if (localIncrementalChange != null) { 
localIncrementalChange.access$dispatch( 
"onCreate.(Landroid/os/Bundle;)V", new Object[] { this, 
... }); 
return; 
}

当$change不为空的时候，执行IncrementalChange方法。

2，当我们修改代码中方法的实现之后，点击InstantRun，它会生成对应的patch文件来记录你修改的内容。patch文件中的替换类是在所修改类名的后面追加$override，并实现IncrementalChange接口。

3，生成AppPatchesLoaderImpl类，继承自AbstractPatchesLoaderImpl，并实现getPatchedClasses方法，来记录哪些类被修改了。

4，调用load方法之后，根据getPatchedClasses返回的修改过的类的列表，去加载对应的$override类，然后把原有类的$change设置为对应的实现了IncrementalChange接口的$override类。

Instant Run运行机制总结

Instant Run运行机制主要涉及到热部署、温部署和冷部署，主要是在第一次运行，app运行时期，有代码修改时。

第一次编译

1.把Instant-Run.jar和instant-Run-bootstrap.jar打包到主dex中
2.替换AndroidManifest.xml中的application配置
3.使用asm工具，在每个类中添加$change，在每个方法前加逻辑
4.把源代码编译成dex，然后存放到压缩包instant-run.zip中

app运行时

1.获取更改后资源resource.ap_的路径
2.设置ClassLoader。setupClassLoader：
使用IncrementalClassLoader加载apk的代码，将原有的BootClassLoader → PathClassLoader改为BootClassLoader → IncrementalClassLoader → PathClassLoader继承关系。
3.createRealApplication：
创建apk真实的application
4.monkeyPatchApplication
反射替换ActivityThread中的各种Application成员变量
5.monkeyPatchExistingResource
反射替换所有存在的AssetManager对象
6.调用realApplication的onCreate方法
7.启动Server，Socket接收patch列表

有代码修改时

1.生成对应的$override类
2.生成AppPatchesLoaderImpl类，记录修改的类列表
3.打包成patch，通过socket传递给app
4.app的server接收到patch之后，分别按照handleColdSwapPatch、handleHotSwapPatch、handleResourcePatch等待对patch进行处理
5.restart使patch生效

在Android插件化、Android热修复、apk加壳/脱壳中借鉴了Instant Run运行机制，所以理解Instant Run运行机制对于向更深层次的研究是很有帮助的，对于我们自己书写框架也是有借鉴意义的。