设置与桌面相同的action和category
安卓系统桌面也是一个activity，安卓桌面的action和category是：
<activity
    android:name="com.sxt.day04_07_twoaction.MainActivity"
    android:label="@string/app_name" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />项目入口acticity

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>
给自己的acticity设置的和桌面一样，会弹出窗口选择是启动安卓系统桌面的activity还是我们自己的activity。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/btnHome"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="启动桌面Activity" />

</LinearLayout>

package com.sxt.day04_07_twoaction;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;

public class MainActivity extends Activity implements OnClickListener{

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

    private void setListener() {
        findViewById(R.id.btnHome).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        Intent intent=new Intent();
        switch (v.getId()) {
        case R.id.btnHome:
            intent.addCategory(Intent.CATEGORY_HOME);
            intent.setAction(Intent.ACTION_MAIN);//这里用常量，也可以写字符串
            break;
        }
        startActivity(intent);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.sxt.day04_07_twoaction"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.sxt.day04_07_twoaction.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="com.sxt.day04_07_twoaction.SecondActivity"   //要启动的activity的java类
            android:label="@string/title_activity_second" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.DEFAULT"/>与桌面activity相同的时候也要加上这个，然后再设置一个category
                <category android:name="android.intent.category.HOME"/>
            </intent-filter>
        </activity>
    </application>

</manifest>

package com.sxt.day04_07_twoaction;

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

public class SecondActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);  //加载xml文件
        Log.i("main","SecondActivity");
    }

}

<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=".SecondActivity" >

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

</RelativeLayout>