Android Window、PhoneWindow、WindowManager、Activity学习心得第一弹

来源：开发者投稿于 2019-03-29 被查看 46289 次评论：40

Android Window、PhoneWindow、WindowManager、Activity学习心得第一弹

阅读本文，你首先需要理解 Context 上下文环境，Window 窗口的准确含义。那么，接下来，我们首先从Activity的启动开始。（本文重点不在启动详细信息@

Android应用程序的Activity启动过程简要介绍和学习计划

）。我们需要知道Activity有显式启动和隐式启动两种，但是不管是什么启动方式。我们要知道借助于应用程序框架层的ActivityManagerService服务进程。目录（源码目录/frameworks/base/services/java/com/android/server/am/ActivityManagerService.java）以后我将用 Android = 源码目录（默认为Android4.4）在Android应用程序框架层中，ActivityManagerService是一个非常重要的接口，它不但负责启动Activity和Service，还负责管理Activity和Service。

Android应用程序框架层中的ActivityManagerService启动Activity的过程大致如下图所示：

具体启动过程不再做过多赘述，我们这里只需要知道通过ActivityManagerService把这个启动Activity的操作转发给ActivityThread，ActivityThread通过ClassLoader导入相应的Activity类，然后把它启动起来。

目录（Android4.4/frameworks/base/core/java/android/app/ActivityThread.java）

那么，我们下一步进入到ActivityThread执行handleLaunchActivity

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent)
{
.........
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
......
handleResumeActivity(r.token, false, r.isForward,!r.activity.mFinished && !r.startsNotResumed);
.......
}
.....
}

而在performLaunchActivity中

public final class ActivityThread {

	......

	private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
		
		ActivityInfo aInfo = r.activityInfo;
		if (r.packageInfo == null) {
			r.packageInfo = getPackageInfo(aInfo.applicationInfo,
				Context.CONTEXT_INCLUDE_CODE);
		}

		ComponentName component = r.intent.getComponent();
		if (component == null) {
			component = r.intent.resolveActivity(
				mInitialApplication.getPackageManager());
			r.intent.setComponent(component);
		}

		if (r.activityInfo.targetActivity != null) {
			component = new ComponentName(r.activityInfo.packageName,
				r.activityInfo.targetActivity);
		}
//以上 为收集Activity的Package 和 Component  信息
		Activity activity = null;
		try {
			java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
			activity = mInstrumentation.newActivity(
				cl, component.getClassName(), r.intent);
			r.intent.setExtrasClassLoader(cl);
			if (r.state != null) {
				r.state.setClassLoader(cl);
			}
		} catch (Exception e) {
			......
		}
//通过ClassLoade 根据收集的信息把你的Activity加载进来
		try {
			Application app = r.packageInfo.makeApplication(false, mInstrumentation);
//根据AndroidManifest.xml配置文件中的Application标签的信息来创建
			......

			if (activity != null) {
				ContextImpl appContext = new ContextImpl();
				appContext.init(r.packageInfo, r.token, this);
				appContext.setOuterContext(activity);
				CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
				Configuration config = new Configuration(mConfiguration);
				......
				activity.attach(appContext, this, getInstrumentation(), r.token,
					r.ident, app, r.intent, r.activityInfo, title, r.parent,
					r.embeddedID, r.lastNonConfigurationInstance,
					r.lastNonConfigurationChildInstances, config);
//这里正式开始我们的窗口创建
				if (customIntent != null) {
					activity.mIntent = customIntent;
				}
				r.lastNonConfigurationInstance = null;
				r.lastNonConfigurationChildInstances = null;
				activity.mStartedActivity = false;
				int theme = r.activityInfo.getThemeResource();
				if (theme != 0) {
					activity.setTheme(theme);
				}

				activity.mCalled = false;
				mInstrumentation.callActivityOnCreate(activity, r.state);
				......
				r.activity = activity;
				r.stopped = true;
				if (!r.activity.mFinished) {
					activity.performStart();
					r.stopped = false;
				}
				if (!r.activity.mFinished) {
					if (r.state != null) {
						mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
					}
				}
				if (!r.activity.mFinished) {
					activity.mCalled = false;
					mInstrumentation.callActivityOnPostCreate(activity, r.state);
					if (!activity.mCalled) {
						throw new SuperNotCalledException(
							"Activity " + r.intent.getComponent().toShortString() +
							" did not call through to super.onPostCreate()");
					}
				}
			}
			r.paused = true;

			mActivities.put(r.token, r);

		} catch (SuperNotCalledException e) {
			......

		} catch (Exception e) {
			......
		}

		return activity;
	}

	......
}

以上关于ActivityThread 启动Activity，如果还有什么不明白的请查看 @Android应用程序启动过程源代码分析
紧接着上一步，我们跟踪到Activity的attach 目录（Android 4.4 /frameworks/base/core/java/android/app/Activity.java）

final void attach(Context context,ActivityThread aThread,
 Instrumentation instr, IBinder token,Application application, 
Intent intent, ActivityInfo info, CharSequence title,Application application,
 Intent intent, ActivityInfo info, CharSequence title,Configuration config) 
{
attach(context, aThread, instr, token, 0, application,intent, info, title, 
parent, id,lastNonConfigurationInstances, config);
}

final void attach(Context context, ActivityThread aThread,
Instrumentation instr, IBinder token, int ident,Application application,

 Intent intent, ActivityInfo info,CharSequence title, Activity parent, String id,NonConfigurationInstances lastNonConfigurationInstances,
Configuration config) {
.....
mWindow = PolicyManager.makeNewWindow(this);
mWindow.setCallback(this);
......
//基本信息初始化
.......
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
if (mParent != null) {
      mWindow.setContainer(mParent.getWindow());
}
 mWindowManager = mWindow.getWindowManager();     ......}

走到这里，我们终于看到了我们的Window 我们知道，在Android中，每一个Activity组件都有一个关联的Window对象，用来描述一个应用程序窗口。每一个应用程序窗口内部又包含有一个View对象，用来描述应用程序窗口的视图。应用程序窗口视图是真正用来实现UI内容和布局的，也就是说，每一个Activity组件的UI内容和布局都是通过与其所关联的一个Window对象的内部的一个View对象来实现的目录（Android 4.4/frameworks/base/core/java/com/android/internal/policy/PolicyManager.java）

public final class PolicyManager {
private static final String POLICY_IMPL_CLASS_NAME =
"com.android.internal.policy.impl.Policy";
private static final IPolicy sPolicy;
static {
try{
Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
sPolicy = (IPolicy)policyClass.newInstance();
}catch(....){
.......
}
}
public static Window makeNewWindow(Context context) {
return sPolicy.makeNewWindow(context);
}

public static LayoutInflater makeNewLayoutInflater(Context context) {
return sPolicy.makeNewLayoutInflater(context);
}

public static WindowManagerPolicy makeNewWindowManager() {
return sPolicy.makeNewWindowManager();
}
}

相应的Policy中目录（Android 4.4 /frameworks/base/policy/src/com/android/internal/policy/impl/Policy.java）

public class Policy implements IPolicy {
private static final String[] preload_classes = {
"com.android.internal.policy.impl.PhoneLayoutInflater",
"com.android.internal.policy.impl.PhoneWindow",
.....
};

static {
for (String s : preload_classes) {
try{
Class.forName(s);
}catch (ClassNotFoundException ex) {
}
}
public Window makeNewWindow(Context context) {
return new PhoneWindow(context);
}
public LayoutInflater makeNewLayoutInflater(Context context) {
return new PhoneLayoutInflater(context);
}
public WindowManagerPolicy makeNewWindowManager() {
return new PhoneWindowManager();
}
}

这里我们开始创建继承了Window的PhoneWindow 在这里，如果我们想继续往下分析，我们必须知道

一、PhoneWindow实现了Window 二、
应用程序窗口内部所包含的视图对象的实际类型为DecorView。DecorView类继承了View类，是作为容器（ViewGroup）来使用的

Android Window、PhoneWindow、WindowManager、Activity学习心得第一弹