Create Context 的理解.md

blogs/Android/Framework/Interview/应用进程相关/Context 的理解.md

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+---
+谈谈你对 Context 的理解？
+---
+
+1. 了解 Context 的作用
+2. 熟悉 Context 初始化流程
+3. 深入理解不同应用组件之间 Context 的区别
+
+#### 问题
+
+1. 应用里面有多少个 Context？不同的 Context 之间有什么区别？
+2. Activity 里的 this 和 getBaseContext 有什么区别？
+3. getApplication 和 getApplicationContext 有什么区别？
+4. 应用组件的构造，onCreate、attachBaseContext 调用顺序？
+
+
+
+```java
+class ContextImpl extends Context {
+	final ActivityThread mMainThread;
+	final LoadedApk mPackageInfo;
+	
+	private final ResourcesManager mResourcesManager;
+    private final Resource mResources;
+    
+	private Resources.Theme mTheme = null;
+    private PackageManager mPackageManager;
+	
+	final Object[] mServiceCache = SystemServiceRegistry.createServiceCache();
+}
+```
+
+#### Context 是在哪创建的？
+
+Application ：
+
+1. 继承关系
+
+   Application <- ContextWrapper <- Context
+
+2. 调用顺序
+
+   \<init> -> attachBaseContext -> onCreate
+
+Activity：
+
+```java
+private Activity performLaunchActivity() {
+	Activity activity = null;
+	activity = mInstrumentation.newActivity();
+	
+	Application app = r.packageInfo.makeApplication();
+	Context appContext = createBaseContextForActivity(r, activity);
+	activity.attach(appContext, app, ...);
+	
+	activity.onCreate();
+	return activity;
+}
+```
+
+1. 继承关系
+
+   Activity <- ContextThemeWrapper <- ContextWrapper
+
+2. 调用顺序
+
+   \<init> -> attachBaseContext -> onCreate
+
+Service:
+
+```java
+private void handleCreateService(CreateServiceData data) {
+	Service service = null;
+    service = (Service) cl.loadClass(data.info.name).newInstance();
+    
+    ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
+    context.setOuterContext(service);
+    
+    Application app = packageInfo.makeApplication();
+    service.attach(context, app);
+    service.onCreate();
+}
+```
+