（二）Activity启动模式

一、标准模式（standrard)

1.当新建一个Activity时，默认情况下就是标准模式，也可以通过AndroidManifest文件显示指定其launchMode为standard

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:launchMode="standard"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
2.通过getTaskId（）获取任务id号，通过toString（）获取当前Activity的属性

public class MainActivity extends Activity {
    private TextView tv;

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

        tv=(TextView)findViewById(R.id.tv);
        tv.setText(String.format("TaskID:%d 
ActivatyName:%s",getTaskId(),toString()));

        findViewById(R.id.btnStartMainActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this,MainActivity.class));
            }
        });
    }
}
3.标准模式下所有的Activity都位于同一个任务栈中，先进后出，启动的第一个Activity位于栈底，之后一次叠加。
二、SingleTop模式
SingleTop模式下，处于任务栈栈顶的Activity只能打开一个，其余的可以打开多个。
2.1 AndroidManifest.xml

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

    <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"
            android:launchMode="singleTop" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".BActivity"
            android:label="@string/title_activity_b"
            android:launchMode="singleTop">
        </activity>
    </application>

</manifest>
2.2 activity_main.xml

<LinearLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

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

    <Button
        android:textAllCaps="false"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="启动MainActivity"
        android:id="@+id/btnStartMainActivity"
        android:layout_gravity="center_horizontal" />

    <Button
        android:textAllCaps="false"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="启动BActivity"
        android:id="@+id/btnStartBActivity"
        android:layout_gravity="center_horizontal" />
</LinearLayout>
2.3 MainActivity.java

package com.example.shiyanshi.activitystartself;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;


public class MainActivity extends Activity {
    private TextView tv;

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

        tv=(TextView)findViewById(R.id.tv);
        tv.setText(String.format("TaskID:%d 
ActivatyName:%s",getTaskId(),toString()));

        findViewById(R.id.btnStartMainActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this, MainActivity.class));
            }
        });
        findViewById(R.id.btnStartBActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this,BActivity.class));
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}
2.4 activity_b.xml

<LinearLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.example.shiyanshi.activitystartself.BActivity">

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

    <Button
        android:textAllCaps="false"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="启动MainActivity"
        android:id="@+id/btnStartMainActivity"
        android:layout_gravity="center_horizontal" />

    <Button
        android:textAllCaps="false"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="启动BActivity"
        android:id="@+id/btnStartBActivity"
        android:layout_gravity="center_horizontal" />

</LinearLayout>
2.5 BActivity.java

package com.example.shiyanshi.activitystartself;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;


public class BActivity extends Activity {
    private TextView tv;

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

        tv=(TextView)findViewById(R.id.tv);
        tv.setText(String.format("TaskID:%d 
ActivatyName:%s", getTaskId(), toString()));
        findViewById(R.id.btnStartMainActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(BActivity.this, MainActivity.class));
            }
        });
        findViewById(R.id.btnStartBActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(BActivity.this, BActivity.class));
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_b, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}
三、singleTask模式
singleTask模式下，当打开两个不同的Activity时，此时再打开一个和栈底Activity同类型的Activity时，会把栈顶的Activity弹出，任务栈中只有了一个Activity，再按一次返回就可以直接退出应用程序。
直接修改上面AndroidManifest.xml文件，修改launchMode为singleTask便可

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

    <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"
            android:launchMode="singleTask" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".BActivity"
            android:label="@string/title_activity_b"
            android:launchMode="singleTask"
            >
        </activity>
    </application>

</manifest>

四、singleInstance模式
两个不同Activity的任务ID不相同，每一个任务栈中只有一个Activity实例，两个不同的Activity之间可以相互切换，点击一次返回会返回到上一个Activity，再点击一次返回才会退出应用程序。

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

    <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"
            android:launchMode="singleInstance" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".BActivity"
            android:label="@string/title_activity_b"
            android:launchMode="singleInstance"
            >
        </activity>
    </application>

</manifest>