Activity的生命周期

一.摘要　　

　　一个完整的Activity的生命周期有6个回调函数。

//创建Activity
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
//Activity快要变成可见的
    @Override
    protected void onStart() {
        super.onStart();
    }
//Activity变成可见的，处于运行状态
    @Override
    protected void onResume() {
        super.onResume();
    }
//其他Activity获得用户焦点，（Activity快要暂停了）
    @Override
    protected void onPause() {
        super.onPause();
    }
//Activity不再可见，处于停止状态
    @Override
    protected void onStop() {
        super.onStop();
    }
//Activity快要被销毁了
    @Override
    protected void onDestroy() {
        super.onDestroy()；
   ｝
  }

这些方法定义了Activity完整的生命周期，实现这些方法，我们能监控Activity生命周期中的三个嵌套循环(monitor three nested loops in the activity lifecycle)

1.Activity的entire lifetime（全部的生命期）发生在

调用onCreate()和调用onDestory()之间。

在onCreate()方法中执行全局状态的建立(例如定义布局)，在onDestroy()方法中释放所有保存的资源。

2.Activity的visible lifetime(可见的生命期)发生在

调用onStart()和onStop（)之间。

在这个期间，用户能在屏幕上看见Activity，和它进行交互。

系统在Activity的完整寿命中可能多次调用onStart()和onStop(),正如Activity交替地对用户可见或隐藏。

3Activity的foreground lifetime (前台的生命期)发生在

调用onResume()和onPause()之间。

在这期间，Activity在屏幕上所有其他Activity的前面，有用户输入焦点。

一个Activity能频繁的在前台进入和出去之间转变。

下面这张图很好的讲解了Activity的生命周期和上面说的三种生命期：

Activity的生命周期

二. 实例

下面通过一个Demo来学习以下Activity的生命周期:Demo很简单，一共三个Activity，MainActivity和NormalActivity和DialogActivity。MainActivity里面有两个按钮，分别可以跳转到NormalActivity和DialogActivity。NormalActivity和DialogActivity的唯一区别就是DialogActivity指定了Activity的主题为Dialog，即在AndroidManifest文件里面注册后者多了一句

android:theme="@android:style/Theme.Dialog"

MainActivity：

public class MainActivity extends Activity {
    public static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "MainActivity_onCreate");
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

            Button startNormalActivity = (Button) findViewById(R.id.start_normal_button);
            Button startDialogActivity = (Button) findViewById(R.id.start_dialog_button);

        startNormalActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, NormalActivity.class);
                startActivity(intent);
            }
        });

        startDialogActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, DialogActivity.class);
                startActivity(intent);
            }
        });

    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.d(TAG, "MainActivity_onStart");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "MainActivity_onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "MainActivity_onPause");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "MainActivity_onStop");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "MainActivity_onDestroy");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.d(TAG, "MainActivity_onRestart");
    }

}

MainActivity

public class NormalActivity extends Activity { public static final String TAG = "NormalActivity"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d(TAG,"NormalActivity_onCreate"); requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.normal_layout); } @Override protected void onStart() { super.onStart(); Log.d(TAG, "NormalActivity_onStart"); } @Override protected void onResume() { super.onResume(); Log.d(TAG, "NormalActivity_onResume"); } @Override protected void onPause() { super.onPause(); Log.d(TAG, "NormalActivity_onPause"); } @Override protected void onStop() { super.onStop(); Log.d(TAG, "NormalActivity_onStop"); } @Override protected void onDestroy() { super.onDestroy(); Log.d(TAG, "NormalActivity_onDestroy"); } @Override protected void onRestart() { super.onRestart(); Log.d(TAG, "NormalActivity_onRestart"); } }

package com.example.haisun.activitylifecycle; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Window; /** * Created by HaiSun on 2015/10/1. */ public class DialogActivity extends Activity { public static final String TAG = "DialogActivity"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d(TAG,"DialogActivity_onCreate"); requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.dialog_layout); } @Override protected void onStart() { super.onStart(); Log.d(TAG, "NDialogActivity_onStart"); } @Override protected void onResume() { super.onResume(); Log.d(TAG, "DialogActivity_onResume"); } @Override protected void onPause() { super.onPause(); Log.d(TAG, "DialogActivity_onPause"); } @Override protected void onStop() { super.onStop(); Log.d(TAG, "DialogActivity_onStop"); } @Override protected void onDestroy() { super.onDestroy(); Log.d(TAG, "DialogActivity_onDestroy"); } @Override protected void onRestart() { super.onRestart(); Log.d(TAG, "DialogActivity_onRestart"); } }

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.haisun.activitylifecycle" > <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name=".MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".NormalActivity"> </activity> <activity android:name=".DialogActivity" android:theme="@android:style/Theme.Dialog"> </activity> </application> </manifest>

Activity的生命周期

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