Activity

 

每天都在用Activity，但是确从来没有认真看过Activity的源代码，实属遗憾。今天周末，公司加班，来的比较早，正好看看。

 

Activity的源码类注释写的非常细致，几乎和官方文档写的一样细致了， 大致的浏览了一遍，就是简单的介绍。但是里面的内容都非常重要，涉及到以下几个方面的内容。

Topics covered here:

1. Activity Lifecycle
2. Configuration Changes
3. Starting Activities and Getting Results
4. Saving Persistent State
5. Permissions
6. Process Lifecycle

看下类声明，继承了一个类，实现了几个接口：

public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks

LayoutInflater.Factory这个是和初始化XML文件相关的接口；

Window.Callback这个接口有很多回调方法；

KeyEvent.Callback onKeyDown等回调方法都在这个接口里；

OnCreateContextMenuListener context menu被创建时的回调；

ComponentCallbacks ：

看注释：The set of callback APIs that are common to all application components (android.app.Activity, android.app.Service, ContentProvider, and android.app.Application).  这个接口只有2个方法：onLowMemory，onConfigurationChanged。

 

再看继承的这个类：

/**
 * A ContextWrapper that allows you to modify the theme from what is in the
 * wrapped context.
 */
public class ContextThemeWrapper extends ContextWrapper

 

/**
 * Proxying implementation of Context that simply delegates all of its calls to
 * another Context.  Can be subclassed to modify behavior without changing
 * the original Context.
 */
public class ContextWrapper extends Context

 

/**
 * Interface to global information about an application environment.  This is
 * an abstract class whose implementation is provided by
 * the Android system.  It
 * allows access to application-specific resources and classes, as well as
 * up-calls for application-level operations such as launching activities,
 * broadcasting and receiving intents, etc.
 */

public abstract class Context

 

 

里面还有很多涉及到生命周期的方法，比如：oncreate onresume onstop onNewIntent等，也有getParent，getWindow，getWindowManager等方法，还有menu，context menu的创建，dialog的创建，还有一些keyevent和dispatchevent等；还有这个runOnUiThread方法，看其源码，有点意思：

 public final void runOnUiThread(Runnable action) {
        if (Thread.currentThread() != mUiThread) {
            mHandler.post(action);
        } else {
            action.run();
        }
    }

暂时只看出了这么多，后续再补充。

 

还有在android.app这个包下，有Activity,ActivityGroup,ActivityManager,Application等类，如图所示：