Activity共有四种启动模式：standard，singleTop，singleTask，singleInstance

为了方便描述和理解，布局文件、Manifest文件和各个java文件如下：

AndoirdManifest文件

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.activitylaunchmode"

    android:versionCode="1"

    android:versionName="1.0" >

    <uses-sdk

        android:minSdkVersion="19"

        android:targetSdkVersion="21" />

    <application

        android:allowBackup="true"

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name"

        android:theme="@style/AppTheme" >

        <activity

            android:launchMode="standard"

            android:screenOrientation="portrait"

            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:launchMode="singleTop"

            android:screenOrientation="portrait"

            android:name=".SecondActivity">

        </activity>

        <activity

            android:launchMode="singleTask"

            android:screenOrientation="portrait"

            android:name=".ThirdActivity">

        </activity>

        <activity

            android:launchMode="singleInstance"

            android:screenOrientation="portrait"

            android:name=".FourActivity">

        </activity>

    </application>

</manifest>

　　4个Activity分别对应一种启动模式：

　　　　MainActivity ----> standard (默认模式，写不写都可以)

　　　　SecondActivity ----> singleTop

　　　　ThirdActivty ----> singleTask

　　　　FourActivity ----> singleInstance

布局文件 activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    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="com.example.activitylaunchmode.MainActivity" >

    <TextView

        android:id="@+id/mTextView"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        />

    <Button

        android:layout_below="@id/mTextView"

        android:id="@+id/buttonOne"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Button1"

        />

    <Button

        android:id="@+id/buttonTwo"

        android:text="Button2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_toRightOf="@id/buttonOne"

           android:layout_below="@id/mTextView"

        />

    <Button

        android:id="@+id/buttonThree"

        android:text="Button3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@id/buttonOne"

        />

    <Button

        android:id="@+id/buttonFour"

        android:text="Button4"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@id/buttonTwo"

        android:layout_toRightOf="@id/buttonThree"

        />

</RelativeLayout>

MainActivity.java

package com.example.activitylaunchmode;

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;

import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener{

    private static final String TAG = "MainActivity";

    TextView tv;

    Button ButtonOne;

    Button ButtonTwo;

    Button ButtonThree;

    Button ButtonFour;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.mTextView);

        tv.setText("MainActivity");

        ButtonOne = (Button) findViewById(R.id.buttonOne);

        ButtonOne.setOnClickListener(this);

        ButtonTwo = (Button) findViewById(R.id.buttonTwo);

        ButtonTwo.setOnClickListener(this);

        ButtonThree = (Button) findViewById(R.id.buttonThree);

        ButtonThree.setOnClickListener(this);

        ButtonFour = (Button) findViewById(R.id.buttonFour);

        ButtonFour.setOnClickListener(this);

    }

    @Override

    protected void onNewIntent(Intent intent) {

        // TODO Auto-generated method stub

        super.onNewIntent(intent);

        Log.d(TAG, "onNewIntent");

    }

    @Override

    public void onClick(View v) {

        // TODO Auto-generated method stub

        switch (v.getId()) {

        case R.id.buttonOne:

            Intent mainIntent = new Intent(this,MainActivity.class);

            startActivity(mainIntent);

            break;

        case R.id.buttonTwo:

            Intent secondIntent = new Intent(this,SecondActivity.class);

            startActivity(secondIntent);

            break;

        case R.id.buttonThree:

            Intent ThirdIntent = new Intent(this,ThirdActivity.class);

            startActivity(ThirdIntent);

            break;

        case R.id.buttonFour:

            Intent FourIntent = new Intent(this,FourActivity.class);

            startActivity(FourIntent);

            break;

        }

    }

}

SecondActivity.java

package com.example.activitylaunchmode;

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;

import android.widget.TextView;

public class SecondActivity extends Activity implements OnClickListener {

    private static final String TAG = "SecondActivity";

    TextView tv;

    Button ButtonOne;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.mTextView);

        tv.setText("SecondActivity");

        ButtonOne = (Button) findViewById(R.id.buttonOne);

        ButtonOne.setOnClickListener(this);

    }

    @Override

    protected void onNewIntent(Intent intent) {

        // TODO Auto-generated method stub

        super.onNewIntent(intent);

        Log.d(TAG, "onNewIntent");

    }

    @Override

    public void onClick(View v) {

        // TODO Auto-generated method stub

        switch (v.getId()) {

        case R.id.buttonOne:

            Intent secondIntent = new Intent(this,SecondActivity.class);

            startActivity(secondIntent);

            break;

        }

    }

}

ThirdActivity.java

package com.example.activitylaunchmode;

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;

import android.widget.TextView;

public class ThirdActivity extends Activity implements OnClickListener {

    private static final String TAG = "ThirdActivity";

    TextView tv;

    Button ButtonOne;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.mTextView);

        tv.setText("ThirdActivity");

        ButtonOne = (Button) findViewById(R.id.buttonOne);

        ButtonOne.setOnClickListener(this);

    }

    @Override

    protected void onNewIntent(Intent intent) {

        // TODO Auto-generated method stub

        super.onNewIntent(intent);

        Log.d(TAG, "onNewIntent");

    }

    @Override

    public void onClick(View v) {

        // TODO Auto-generated method stub

        switch (v.getId()) {

        case R.id.buttonOne:

            Intent mainIntent = new Intent(this,MainActivity.class);

            startActivity(mainIntent);

            break;

        default:

            break;

        }

    }

}

FourActivity.java

package com.example.activitylaunchmode;

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;

import android.widget.TextView;

public class FourActivity extends Activity implements OnClickListener {

    private static final String TAG = "FourActivity";

    TextView tv;

    Button ButtonOne;

    Button ButtonTwo;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.mTextView);

        tv.setText("FourActivity");

        ButtonOne = (Button) findViewById(R.id.buttonOne);

        ButtonOne.setOnClickListener(this);

    }

    @Override

    protected void onNewIntent(Intent intent) {

        // TODO Auto-generated method stub

        super.onNewIntent(intent);

        Log.d(TAG, "onNewIntent");

    }

    @Override

    public void onClick(View v) {

        // TODO Auto-generated method stub

        switch (v.getId()) {

        case R.id.buttonOne:

            Intent MainIntent = new Intent(this,MainActivity.class);

            startActivity(MainIntent);

            break;

        case R.id.buttonFour:

            Intent FourIntent = new Intent(this,FourActivity.class);

            startActivity(FourIntent);

        default:

            break;

        }

    }

}

各个启动模式差异探究：

　　1）standard: 默认模式，每启动一个activity都会在Task中创建一个，back键会依次从栈中退出

　　　　MainActivity的启动模式是standard, 点击Button1,会再启动一个MainActivity.

　　　　通过adb shell dumpsys activity命令，我们能看到在Task中存在两个MainActivity.

    Task id #

      TaskRecord{2cfa2efd # A=com.example.activitylaunchmode U= sz=}

      Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity }

        Hist #: ActivityRecord{37783c3a u0 com.example.activitylaunchmode/.MainActivity t48}

          Intent { cmp=com.example.activitylaunchmode/.MainActivity }

          ProcessRecord{358547f2 :com.example.activitylaunchmode/u0a134}

        Hist #: ActivityRecord{363c8000 u0 com.example.activitylaunchmode/.MainActivity t48}

          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity bnds=[,][,] }

          ProcessRecord{358547f2 :com.example.activitylaunchmode/u0a134}

    Running activities (most recent first):

      TaskRecord{2cfa2efd # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{37783c3a u0 com.example.activitylaunchmode/.MainActivity t48}

        Run #: ActivityRecord{363c8000 u0 com.example.activitylaunchmode/.MainActivity t48}

　　2）singleTop：如果要启动的Activity在栈顶，则不会重新创建

　　　 SecondActivity的启动模式是singleTop, 点击MainActivity中的Button2,会创建一个SecondActivity,再点击SecondActivity中的Button1,会重新启动　SecondActivity.

　　　　通过adb命令，我们可以看到，Task中只有MainActivity和SecondActivity两个Activity,第二次点击并没有重新创建。从log中，我们可以看到，第二次点击启动SecondActivity,只是调用了前一个SecondActivity的onNewIntent方法。

    Task id #

      TaskRecord{fb41e01 # A=com.example.activitylaunchmode U= sz=}

      Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity }

        Hist #: ActivityRecord{1ea62f6c u0 com.example.activitylaunchmode/.SecondActivity t51}

          Intent { cmp=com.example.activitylaunchmode/.SecondActivity }

          ProcessRecord{69b44a6 :com.example.activitylaunchmode/u0a134}

        Hist #: ActivityRecord{27f7bb0a u0 com.example.activitylaunchmode/.MainActivity t51}

          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity bnds=[,][,] }

          ProcessRecord{69b44a6 :com.example.activitylaunchmode/u0a134}

    Running activities (most recent first):

      TaskRecord{fb41e01 # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{1ea62f6c u0 com.example.activitylaunchmode/.SecondActivity t51}

        Run #: ActivityRecord{27f7bb0a u0 com.example.activitylaunchmode/.MainActivity t51}

　　3）singleTask: 任务栈中没有这个Activity,则会在任务栈中创建一个实例，如果任务栈中已经存在，则会将任务栈中的此activity之上的activity全部出栈

　　　　ThirdActivity的启动模式是singleTask, 点击MainActivity中的Button3,启动ThirdActivity,再点击ThirdActivity中的Button1,启动MainActivity，此时的Activity的堆栈信息如下：

    Task id #

      TaskRecord{147eed75 # A=com.example.activitylaunchmode U= sz=}

      Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity }

        Hist #: ActivityRecord{2bf26a69 u0 com.example.activitylaunchmode/.MainActivity t52}

          Intent { cmp=com.example.activitylaunchmode/.MainActivity }

          ProcessRecord{3e2f10a :com.example.activitylaunchmode/u0a134}

        Hist #: ActivityRecord{147e2631 u0 com.example.activitylaunchmode/.ThirdActivity t52}

          Intent { flg=0x10000000 cmp=com.example.activitylaunchmode/.ThirdActivity }

          ProcessRecord{3e2f10a :com.example.activitylaunchmode/u0a134}

        Hist #: ActivityRecord{4e87389 u0 com.example.activitylaunchmode/.MainActivity t52}

          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity bnds=[,][,] }

          ProcessRecord{3e2f10a :com.example.activitylaunchmode/u0a134}

    Running activities (most recent first):

      TaskRecord{147eed75 # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{2bf26a69 u0 com.example.activitylaunchmode/.MainActivity t52}

        Run #: ActivityRecord{147e2631 u0 com.example.activitylaunchmode/.ThirdActivity t52}

        Run #: ActivityRecord{4e87389 u0 com.example.activitylaunchmode/.MainActivity t52}

　　　这个也说明了standard启动模式会重新创建一个Activity.

　　　然后再点击MainActivity中的Button3，启动ThirdActivity,通过adb命令看到的如下：　

    Task id #

      TaskRecord{2553d3b2 # A=com.example.activitylaunchmode U= sz=}

      Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity }

        Hist #: ActivityRecord{33f3f7cd u0 com.example.activitylaunchmode/.ThirdActivity t53}

          Intent { flg=0x10000000 cmp=com.example.activitylaunchmode/.ThirdActivity }

          ProcessRecord{1cdd8f03 :com.example.activitylaunchmode/u0a134}

        Hist #: ActivityRecord{e5f9ea5 u0 com.example.activitylaunchmode/.MainActivity t53}

          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity bnds=[,][,] }

          ProcessRecord{1cdd8f03 :com.example.activitylaunchmode/u0a134}

    Running activities (most recent first):

      TaskRecord{2553d3b2 # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{33f3f7cd u0 com.example.activitylaunchmode/.ThirdActivity t53}

        Run #: ActivityRecord{e5f9ea5 u0 com.example.activitylaunchmode/.MainActivity t53}

　　　　能看到Task中现在只有两个Activity,ThirdActivity并没有重新创建，靠后的一个MainActivity也被弹出栈，从log也能看出调用了onNewIntent方法，

　　4）singleInstance: 只有一个实例，运行于独立的task，启动此Activity的时候如果已经创建，则不会重新创建

　　　　FourActivity的启动模式是singleInstance,点击MainActivity中的Button4，会启动FourActivity

　　　　通过adb shell dumpsys activity命令，我们能看到两个Activity在不同的Task中，　　　　

    Task id #

      TaskRecord{11be8b0d # A=com.example.activitylaunchmode U= sz=}

      Intent { flg=0x10000000 cmp=com.example.activitylaunchmode/.FourActivity }

        Hist #: ActivityRecord{1cd2b9e5 u0 com.example.activitylaunchmode/.FourActivity t55}

          Intent { flg=0x10000000 cmp=com.example.activitylaunchmode/.FourActivity }

          ProcessRecord{358d5ac2 :com.example.activitylaunchmode/u0a134}

    Task id #

      TaskRecord{12e2f0d3 # A=com.example.activitylaunchmode U= sz=}

      Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity }

        Hist #: ActivityRecord{374dcd03 u0 com.example.activitylaunchmode/.MainActivity t54}

          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x30200000 cmp=com.example.activitylaunchmode/.MainActivity bnds=[,][,] }

          ProcessRecord{358d5ac2 :com.example.activitylaunchmode/u0a134}

    Running activities (most recent first):

      TaskRecord{11be8b0d # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{1cd2b9e5 u0 com.example.activitylaunchmode/.FourActivity t55}

      TaskRecord{12e2f0d3 # A=com.example.activitylaunchmode U= sz=}

        Run #: ActivityRecord{374dcd03 u0 com.example.activitylaunchmode/.MainActivity t54}

　　　　如果再点击FourActivity中的Button4,也不会重新创建，从log可以看出，会调用onNewIntent方法，这里就不在贴activity的信息。

　　　 adb shell dumpsys activity activities 也可以看到Task中各个activity的 launchMode.

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Android Activity各启动模式的差异

各个启动模式差异探究：

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