instant-run 源碼地址
仔細過一遍 README, 對 instant-run 就會有一個大體的了解;
instant-run 的目的是方便 Android 開發(fā)者, 減少 build, install, debug 的耗時, 做到修改代碼后在調(diào)試設備上的 APP 不重啟就可以直接看到修改的結(jié)果(雖然 instant-run 沒有完全實現(xiàn));
instant-run 工作模式:
- Hot Swap: 不需要重啟 Actitvity 就可以看到修改結(jié)果
- Cold Swap: 需要重啟 Actitvity 才能看到修改結(jié)果
- Reinstall: 需要重啟 APP 才能看到修改結(jié)果
只修改了源代碼時可以 Hot Swap,
修改了資源文件時需要 Cold Swap,
修改了AndroidManifest.xml 時就需要重啟 APP 了
instant-run 實現(xiàn)方案
Host Swap 的實現(xiàn)方案是 "代理模式", 在 APP 首次運行時, 在編譯期間添加了 instant-install Gradle Task, 當打開了 Android Studio 的 instant-run 功能時, 執(zhí)行 assembleDebug 時依賴執(zhí)行了下面的 Task:
Executing tasks: [:app:assembleDebug]
Configuration on demand is an incubating feature.
:app:buildInfoDebugLoader
:app:preBuild UP-TO-DATE
:app:preDebugBuild UP-TO-DATE
:app:checkDebugManifest
:app:prepareComAndroidSupportAnimatedVectorDrawable2600Alpha1Library
:app:prepareComAndroidSupportAppcompatV72600Alpha1Library
:app:prepareComAndroidSupportConstraintConstraintLayout102Library
:app:prepareComAndroidSupportSupportCompat2600Alpha1Library
:app:prepareComAndroidSupportSupportCoreUi2600Alpha1Library
:app:prepareComAndroidSupportSupportCoreUtils2600Alpha1Library
:app:prepareComAndroidSupportSupportFragment2600Alpha1Library
:app:prepareComAndroidSupportSupportMediaCompat2600Alpha1Library
:app:prepareComAndroidSupportSupportV42600Alpha1Library
:app:prepareComAndroidSupportSupportVectorDrawable2600Alpha1Library
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources
:app:incrementalDebugJavaCompilationSafeguard UP-TO-DATE
:app:javaPreCompileDebug
:app:compileDebugJavaWithJavac
:app:compileDebugJavaWithJavac - is not incremental (e.g. outputs have changed, no previous execution, etc.).
:app:mergeDebugShaders UP-TO-DATE
:app:compileDebugShaders UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:processDebugJavaRes NO-SOURCE
:app:transformResourcesWithMergeJavaResForDebug UP-TO-DATE
:app:packageInstantRunResourcesDebug UP-TO-DATE
:app:fastDeployDebugExtractor UP-TO-DATE
:app:generateDebugInstantRunAppInfo UP-TO-DATE
:app:checkManifestChangesDebug
:app:transformClassesWithExtractJarsForDebug UP-TO-DATE
:app:transformClassesWithInstantRunVerifierForDebug
:app:transformClassesWithDependencyCheckerForDebug UP-TO-DATE
:app:compileDebugNdk NO-SOURCE
:app:mergeDebugJniLibFolders UP-TO-DATE
:app:transformNativeLibsWithMergeJniLibsForDebug UP-TO-DATE
:app:transformNativeLibsAndResourcesWithJavaResourcesVerifierForDebug UP-TO-DATE
:app:transformClassesWithInstantRunForDebug
:app:transformClassesEnhancedWithInstantReloadDexForDebug
:app:incrementalDebugTasks
:app:preColdswapDebug
:app:transformClassesWithInstantRunSlicerForDebug
:app:transformClassesWithDexForDebug
:app:validateSigningDebug
:app:transformDexWithInstantRunDependenciesApkForDebug
:app:transformDexWithInstantRunSlicesApkForDebug
:app:transformNativeLibsWithStripDebugSymbolForDebug UP-TO-DATE
:app:packageDebug UP-TO-DATE
:app:buildInfoGeneratorDebug
:app:compileDebugSources
:app:assembleDebug
BUILD SUCCESSFUL
Total time: 2.828 secs
可以看到有一些關(guān)于 instant-run 的 task
:app:incrementalDebugJavaCompilationSafeguard UP-TO-DATE
:app:packageInstantRunResourcesDebug UP-TO-DATE
:app:generateDebugInstantRunAppInfo UP-TO-DATE
:app:transformClassesWithInstantRunVerifierForDebug
:app:transformClassesWithInstantRunForDebug
:app:transformClassesEnhancedWithInstantReloadDexForDebug
:app:incrementalDebugTasks
:app:transformClassesWithInstantRunSlicerForDebug
:app:transformDexWithInstantRunDependenciesApkForDebug
:app:transformDexWithInstantRunSlicesApkForDebug
那這些額外的 task 在 APP 編譯期間做了哪些工作?
舉個例子, APP 源碼中有一個 class A:
package com.google.android.foo;
public class A {
int intField;
public int someMethod() {
return intField;
}
}
instant-run 在首次編譯期間在 class A 中添加了一個靜態(tài)變量, 并在方法實現(xiàn)中先判斷新加的變量是否為空, 不為空就執(zhí)行 access$dispatch 方法, 并且不執(zhí)行原有的語句, 這就是 "代理模式":
package com.google.android.foo;
public class A {
static IncrementalChange $change = null;
int intField;
public int someMethod() {
if ($change != null) {
return $change.access$dispatch("someMethod_()I", this)
}
return intField;
}
}
查看 instant-run 源碼, 發(fā)現(xiàn) IncrementalChange 只是一個簡單的接口
package com.android.tools.fd.runtime;
public interface IncrementalChange {
Object access$dispatch(String id, Object... args);
}
接著當開發(fā)者在 Android Studio 中變更了class A 時:
package com.google.android.foo;
public class A {
int intField;
public int someMethod() {
return intField*2; // 改了方法實現(xiàn)
}
}
重新 instant-run 后會產(chǎn)生一個補丁 APK, 其中變更后的 class A 編譯成了
package com.google.android.foo;
public class A$Override implements IncrementalChange {
public static int someMethod(A sender) {
return sender.intField*2;
}
public static Object dispatch(A sender, String methodName, String signature) {
if (methodName.equals("someMethod")) {
return someMethod(sender);
}
}
}
instant-run 生成補丁文件后將補丁發(fā)給已經(jīng)在測試設備上運行的 APP, 這時 APP 已經(jīng)啟動一個 SocketServer , SocketServer 接收到補丁后基于 DexClassLoader 和反射機制將補丁中的 A$Override 賦值給已經(jīng)實例化的 Class A, 這樣再調(diào)用 Class A 的 someMethod 方法時就會執(zhí)行補丁中同名的靜態(tài)someMethod方法, 這樣不需要重新啟動 APP 就能將對源代碼的變更同步到測試設備上, 極大的方便了開發(fā)者調(diào)試代碼.
