Android笔记(5)---Activity生命周期

Android api中提供的Activity生命周期图

创建一个测试项目ActivityLife

在MainActivity.java中

重写onCreate,onStart,onResume,onPause,onStop,onRestart,onDestroy方法

package com.example.activitylife;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Log.e(TAG, "~~~onCreate~~~");
    }

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

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.e(TAG, "~~~onReStart~~~");
    }

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

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

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

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

运行该应用程序

下面是不同操作对应的LogCat输出

打开应用程序时，对应下图过程1

打开应用程序后，按下BACK键时，对应下图过程2

打开应用程序后，按下HOME键时，对应下图过程3

在上一操作的基础上，再次打开应用程序时，对应下图过程4

操作流程图：

========================================================================

参考文章提出的一个问题：

EditText在状态1时输入一个字符串,如"Hello,Android!",再经过3，4状态后无法保持

看到有评论说有id的view，android会自动维护状态

经测试，无论EditText无论有无id,字符串都可保持住

测试如下：

修改res/layout/activity_main.xml，在布局中添加一个EditText控件

<? xml version ="1.0" encoding= "utf-8" ?>
< LinearLayout xmlns:android ="http://schemas.android.com/apk/res/android"
    xmlns:tools ="http://schemas.android.com/tools"
    android:layout_width ="fill_parent"
    android:layout_height ="fill_parent"
    android:orientation ="vertical"
    android:paddingBottom ="@dimen/activity_vertical_margin"
    android:paddingLeft ="@dimen/activity_horizontal_margin"
    android:paddingRight ="@dimen/activity_horizontal_margin"
    android:paddingTop ="@dimen/activity_vertical_margin"
    tools:context =".MainActivity" >

    <TextView
        android:layout_width ="fill_parent"
        android:layout_height ="wrap_content"
        android:text ="@string/hello_world" />

    <EditText
        android:id ="@+id/editText"
        android:layout_width ="fill_parent"
        android:layout_height ="wrap_content"
        android:inputType ="text" />

</ LinearLayout>

再依次运行过程1-->3-->4

在状态1的时候，在EditText控件中写入一个字符串，如Hello,Android!，在经过3，4过程后字符串依旧保持

========================================================================

测试状态5

修改res/layout/main_activity.xml，添加一个Button

<? xml version ="1.0" encoding= "utf-8" ?>
< LinearLayout xmlns:android ="http://schemas.android.com/apk/res/android"
    xmlns:tools ="http://schemas.android.com/tools"
    android:layout_width ="fill_parent"
    android:layout_height ="fill_parent"
    android:orientation ="vertical"
    android:paddingBottom ="@dimen/activity_vertical_margin"
    android:paddingLeft ="@dimen/activity_horizontal_margin"
    android:paddingRight ="@dimen/activity_horizontal_margin"
    android:paddingTop ="@dimen/activity_vertical_margin"
    tools:context =".MainActivity" >

    <TextView
        android:id = "@+id/mainTv"
        android:layout_width ="fill_parent"
        android:layout_height ="wrap_content"
        android:text ="@string/hello_world" />

    <EditText
        android:id = "@+id/mainEt"
        android:layout_width= "fill_parent"
        android:layout_height ="wrap_content"
        android:inputType ="text" />

    <Button
        android:id ="@+id/callDialog"
        android:layout_width ="fill_parent"
        android:layout_height ="wrap_content"
        android:text ="@string/call_dialog" />

</ LinearLayout>

添加一个Activity，SecondActivity

并重写onCreate,onStart,onResume,onPause,onStop,onRestart,onDestroy方法

package com.example.activitylife;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class SecondActivity extends Activity {

    private static final String TAG = "SecondActivity";
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        
        Log.e(TAG, "~~~onCreate~~~");
    }

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

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.e(TAG, "~~~onReStart~~~");
    }

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

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

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

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

修改MainActivity.java

package com.example.activitylife;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

    private static final String TAG = "MainActivity";
    private Button callDialogBut;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Log.e(TAG, "~~~onCreate~~~");

        callDialogBut = (Button) findViewById(R.id.callDialog);
        callDialogBut.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setClass(MainActivity.this, SecondActivity.class);
                startActivity(intent);
            }
        });
    }

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

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.e(TAG, "~~~onReStart~~~");
    }

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

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

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

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

修改AndroidManifest.xml文件

<? xml version ="1.0" encoding= "utf-8" ?>
< manifest xmlns:android ="http://schemas.android.com/apk/res/android"
    package ="com.example.activitylife"
    android:versionCode ="1"
    android:versionName ="1.0" >

    <uses-sdk
        android:minSdkVersion ="8"
        android:targetSdkVersion ="17" />

    <application
        android:allowBackup ="true"
        android:icon ="@drawable/ic_launcher"
        android:label ="@string/app_name"
        android:theme ="@style/AppTheme" >
        < activity
            android:name ="com.example.activitylife.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 =".SecondActivity"
            android:label ="@string/app_name"
            android:theme ="@android:style/Theme.Dialog" >
        </ activity>
    </application >

</ manifest>

启动应用程序后，点击调用对话框按钮，相当于过程5中的onPause

在上一步操作的基础上，点击BACK键，相当于过程5中的onResume

程序运行截图：

启动应用程序

按下调用对话框按钮

再按下BACKUP键

参考文章：

-----------------------

两分钟彻底让你明白Android Activity生命周期(图文)!

Android笔记(5)---Activity生命周期

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