实例一

启动界面的主要功能就是显示一幅启动图像,后台进行系统初始化.

如果是第一次使用本程序,需要初始化本程序的sqlite数据库,建库,建Table,初始化账目数据.

如果不是第一次使用,就进入登记收支记录界面.

界面的具体xml如下:main.xml<?xml version="1.0" encoding="utf-8"?> <RelativeLayout android:id="@+id/RelativeLayout01" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_gravity="center_vertical|center_horizontal" android:layout_height="wrap_content" android:layout_width="wrap_content"> <ImageView android:id="@+id/ImageView01" android:src="@drawable/logo3" android:layout_width="wrap_content" android:layout_height="wrap_content"> </ImageView> <TextView android:id="@+id/TextView01" android:text="@string/welcome" android:layout_below="@id/ImageView01" android:layout_width="wrap_content" android:layout_height="wrap_content"> </TextView> </RelativeLayout>

在这儿我来使用一个小技巧,就是在程序初始化完成后,让图片淡出,然后显示下一个界面.
开始我准备使用一个timer来更新图片的alpha值,后来程序抛出异常Only the original thread that created a view hierarchy can touch its views.
这才发现android 的ui 控件是线程安全的.
这里需要我们在主线程外,再开一个线程更新界面上的图片.可以使用imageview.invalidate
关于如何另开一个线程更新界面的相关代码如下.

//给主线程发送消息更新imageview
mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
imageview.setAlpha(alpha);
imageview.invalidate();

}
};

new Thread(new Runnable() {
public void run() {
while (b < 2) {
try {
//延时2秒后,每50毫秒更新一次imageview
if (b == 0) {
Thread.sleep(2000);
b = 1;
} else {
Thread.sleep(50);
}

updateApp();

} catch (InterruptedException e) {
e.printStackTrace();
}
}

}
}).start();

public void updateApp() {
alpha -= 5;//每次减少alpha 5

if (alpha <= 0) {
b = 2;
Intent in = new Intent(this, com.cola.ui.Frm_Addbills.class);
startActivity(in);//启动下个界面
}

mHandler.sendMessage(mHandler.obtainMessage());
}
 

通过这段代码,我们能够理解android 里面如何对ui视图进行更新.

下篇文章我们来看看sqlite的使用.如何初始化程序.

关于handler,invalidate 的用法,

package com.cola.ui; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.util.Log; import android.view.KeyEvent; import android.widget.ImageView; import android.widget.TextView; public class ColaBox extends Activity { private Handler mHandler = new Handler(); ImageView imageview; TextView textview; int alpha = 255; int b = 0; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); imageview = (ImageView) this.findViewById(R.id.ImageView01); textview = (TextView) this.findViewById(R.id.TextView01); Log.v("ColaBox", "ColaBox start ..."); imageview.setAlpha(alpha); new Thread(new Runnable() { public void run() { initApp(); //初始化程序 while (b < 2) { try { if (b == 0) { Thread.sleep(2000); b = 1; } else { Thread.sleep(50); } updateApp(); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); mHandler = new Handler() { @Override public void handleMessage(Message msg) { super.handleMessage(msg); imageview.setAlpha(alpha); imageview.invalidate(); } }; } public void updateApp() { alpha -= 5; if (alpha <= 0) { b = 2; Intent in = new Intent(this, com.cola.ui.Frm_Addbills.class); startActivity(in); } mHandler.sendMessage(mHandler.obtainMessage()); } public void initApp(){ } }