Android开发小记

时间:2024-08-16 08:05:37

一,下载解压adt-bundle,直接可以用来开发了
二,新建android项目时不勾选创建activity,来看看如何手动创建activity
1,在空项目添加class文件,选择超类为activity

package com.ciaos.demo;

public class DemoActivity extends Activity {

}

2,双击AndroidManifest.xml,选择Application/Add/Activity,配置Name为刚创建的activity

3,右键layout新建Android XML File,选择layout类型,生成main.xml文件,可以通过R.layout.main引用

4,编辑DemoActivity.java文件如下,设置Activity的Layout样式

package com.ciaos.demo;

import com.ciaos.test1.R;

import android.app.Activity;
import android.os.Bundle; public class DemoActivity extends Activity { public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}

5,运行android程序

问题1,如果eclipse编码时提示找不到R.layout.main(自定义layout)
-> 修改DemoActivity.java将import android.R改为import com.ciaos.test1.R

问题2,No Launcher activity found
-> 修改AndroidManifest.xml文件,添加起的那个activity

<activity android:name="com.ciaos.demo.DemoActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

三,通过button控制text的显示
1,设置res/values/strings.xml添加自定义文本

<resources>
<string name="app_name">Test1</string>
<string name="shige">锄禾日当午\n汗滴禾下土</string>
<string name="anniu">按钮显示文本</string>
</resources>

2,拖动Button和TextView控件到main.xml文件,配置TextView隐藏,Button的click事件,xml文件如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="left"
android:orientation="vertical" > <Button
android:id="@+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="onShowClicked"
android:text="@string/anniu" /> <TextView
android:id="@+id/textView1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:visibility="invisible"
android:text="@string/shige" /> </LinearLayout>

3,编辑DemoActivity文件,实现onShowClicked函数

package com.ciaos.demo;

import com.ciaos.test1.R;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView; public class DemoActivity extends Activity { public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
} public void onShowClicked(View view){
TextView tv = (TextView)this.findViewById(R.id.textView1);
tv.setVisibility(View.VISIBLE);
}
}

四,网络请求(应用加载时获取网络图片更新组件UI)

1,编辑AndroidManifest添加Uses Permission

<uses-permission android:name="android.permission.INTERNET"/>

2,编辑工具类ImageHandler,实现下载图片功能

package com.ciaos.demo;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL; import android.graphics.Bitmap;
import android.graphics.BitmapFactory; public class ImageHandler{
private String url = "http://www.baidu.com/img/baidu_sylogo1.gif"; public Bitmap getImage() {
try {
HttpURLConnection connection =
(HttpURLConnection)new URL(url).openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap bitmap = BitmapFactory.decodeStream(input);
input.close();
return bitmap;
} catch (IOException ioe) { return null; }
}
}

3,修改Activity文件,通过子线程调用图片下载服务,使用Handler更新主线程创建的控件

package com.ciaos.demo;

import com.ciaos.test1.R;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.os.Handler;
import android.widget.ImageView; public class DemoActivity extends Activity { Handler handler; public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main); //创建主窗口的引用
handler = new Handler(); //显示等待提示框
final ProgressDialog dialog = ProgressDialog.show(
this,
"Loading",
"Loading the image"); final ImageHandler nh = new ImageHandler();
Thread th = new Thread() {
public void run() {
//获取网页图片
final Bitmap bm = nh.getImage();
handler.post(new Runnable(){
@Override
public void run() {
//更新组件
resetDisplay(bm);
//取消等待提示框
dialog.dismiss();
}});
}
};
th.start();
} private void resetDisplay(Bitmap image){
//更新组件
ImageView iv = (ImageView)this.findViewById(R.id.imgView1);
iv.setImageBitmap(image);
}
}

运行程序后多次横屏竖屏后,程序会出现java.lang.IllegalArgumentException: View not attached to window manager错误,估计是我调用ProgressDialog创建及dismiss方法有误。

多个Activity之间切换

Intent it = new Intent(this,Demo2Activity.class);

startActivity(it);

附操作技巧:如果一个项目是生成jar包供别的android项目调用,可以右键项目->Property->Android(勾选IsLibrary),则每次clean后都会自动生成jar包。