Hello Android例子的內(nèi)部細(xì)節(jié)
在這里，我們將學(xué)習(xí)Hello Android例子的內(nèi)部細(xì)節(jié)或工作原理。愛掏網(wǎng) - it200.com
Android應(yīng)用程序包含不同的組件，如Java源代碼，字符串資源，圖像，清單文件，APK文件等。愛掏網(wǎng) - it200.com讓我們來了解一下Android應(yīng)用程序的項(xiàng)目結(jié)構(gòu)。愛掏網(wǎng) - it200.com
Java源代碼
讓我們來看看由Eclipse IDE創(chuàng)建的Java源文件：
package com.example.helloandroid;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
public class MainActivity extends Activity {//(1)
@Override
protected void onCreate(Bundle savedInstanceState) {//(2)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);//(3)
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {//(4)
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
(1) Activity 是一個(gè)Java類，它在屏幕上創(chuàng)建并顯示一個(gè)默認(rèn)窗口，我們可以在窗口中放置不同的組件，例如按鈕、編輯框、文本視圖、下拉菜單等。愛掏網(wǎng) - it200.com它類似于Java AWT的框架。愛掏網(wǎng) - it200.com
它為Activity提供了生命周期方法，例如onCreate、onStop、onResume等。愛掏網(wǎng) - it200.com
(2) onCreate方法 在Activity類被首次創(chuàng)建時(shí)調(diào)用。愛掏網(wǎng) - it200.com
(3) setContentView(R.layout.activity_main) 提供了關(guān)于我們布局資源的信息。愛掏網(wǎng) - it200.com在這里，我們的布局資源是在activity_main.xml文件中定義的。愛掏網(wǎng) - it200.com
<RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="@string/hello_world" />
</RelativeLayout>
如您所見，一個(gè)TextView是由框架自動(dòng)創(chuàng)建的。愛掏網(wǎng) - it200.com但是這個(gè)字符串的消息是在strings.xml文件中定義的。愛掏網(wǎng) - it200.com @string/hello_world 提供有關(guān)TextView消息的信息。愛掏網(wǎng) - it200.comhello_world屬性的值是在strings.xml文件中定義的。愛掏網(wǎng) - it200.com
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">helloandroid</string>
<string name="hello_world">Hello world!</string>
<string name="menu_settings">Settings</string>
</resources>
您可以從此文件更改hello_world屬性的值。愛掏網(wǎng) - it200.com
生成的R.java文件
這是一個(gè)自動(dòng)生成的文件，包含了res目錄中所有資源的ID。愛掏網(wǎng) - it200.com它是由aapt（Android資源打包工具）生成的。愛掏網(wǎng) - it200.com每當(dāng)您在activity_main上創(chuàng)建任何組件時(shí)，R.java文件中會(huì)創(chuàng)建相應(yīng)的ID，稍后可以在Java源文件中使用它。愛掏網(wǎng) - it200.com
/* AUTO-GENERATED FILE. DO NOT MODIFY.
*
* This class was automatically generated by the
* aapt tool from the resource data it found. It
* should not be modified by hand.
*/
package com.example.helloandroid;
public final class R {
public static final class attr {
}
public static final class drawable {
public static final int ic_launcher=0x7f020000;
}
public static final class id {
public static final int menu_settings=0x7f070000;
}
public static final class layout {
public static final int activity_main=0x7f030000;
}
public static final class menu {
public static final int activity_main=0x7f060000;
}
public static final class string {
public static final int app_name=0x7f040000;
public static final int hello_world=0x7f040001;
public static final int menu_settings=0x7f040002;
}
public static final class style {
/**
Base application theme, dependent on API level. This theme is replaced
by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
Theme customizations available in newer API levels can go in
res/values-vXX/styles.xml, while customizations related to
backward-compatibility can go here.
Base application theme for API 11+. This theme completely replaces
AppBaseTheme from res/values/styles.xml on API 11+ devices.
API 11 theme customizations can go here.
Base application theme for API 14+. This theme completely replaces
AppBaseTheme from BOTH res/values/styles.xml and
res/values-v11/styles.xml on API 14+ devices.
API 14 theme customizations can go here.
*/
public static final int AppBaseTheme=0x7f050000;
/** Application theme.
All customizations that are NOT specific to a particular API-level can go here.
*/
public static final int AppTheme=0x7f050001;
}
}
APK文件
APK文件是由框架自動(dòng)創(chuàng)建的。愛掏網(wǎng) - it200.com如果你想在移動(dòng)設(shè)備上運(yùn)行Android應(yīng)用程序，需要將其傳輸并安裝。愛掏網(wǎng) - it200.com
資源
它包含包括activity_main、strings、styles等資源文件。愛掏網(wǎng) - it200.com
清單文件
它包含有關(guān)包的信息，包括活動(dòng)、服務(wù)、內(nèi)容提供器等組件。愛掏網(wǎng) - it200.com
有關(guān)清單文件更多信息，請(qǐng)?jiān)L問這里： AndroidManifest.xml文件 。愛掏網(wǎng) - it200.com