第一例:HelloWorld

package demo.my.com.myapidemo.app;

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

import demo.my.com.myapidemo.R;

public class HelloWorld extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

}

第一份android代码，离不开helloworld

xml代码

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

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

</RelativeLayout>

资源文件strings

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

    <string name="hello_world">Hello world</string>

</resources>