佈局 

基本上是按照教程走的，但是按照教程上說的並不能真正的居中，有點錯位，按照自己理解修改了 

修改成RelativeLayout屬性為android:gravity="center_vertical"，每個View單獨新增android:layout_centerHorizontal="true"，效果如下：

佈局原始碼如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:gravity="center_vertical" >
    
    <ImageView android:id="@+id/main_logo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/logo"
        android:contentDescription="@string/main_logo_desc"
        android:layout_centerHorizontal="true" />
    
    <TextView android:id="@+id/main_welcome"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/main_logo"
        android:text="@string/main_welcome"
        android:layout_centerHorizontal="true" />

</RelativeLayout>
 

主程式

直接在ImageView元素上設定alpha的方式已經不建議使用，改為直接資源修改

mainLogoDrawable = getResources().getDrawable(R.drawable.logo);
mainLogoDrawable.setAlpha(logoAlpha);

handler建議使用靜態類，具體可以看看網上的解決方案

主程式原始碼

package com.example.diligentpiggy;

import java.lang.ref.WeakReference;

import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;
import android.widget.TextView;


public class MainActivity extends Activity {

    private ImageView mainLogo;
    private TextView mainWelcome;
    
    private Drawable mainLogoDrawable;
    
    private int logoAlpha = 255;
    private static final int UPDATE_ALPHA = -1;
    private static final int START_ACTIVITY = -2;
    
    private static final int THREAD_INIT = 0;
    private static final int THREAD_RUN = 1;
    private static final int THREAD_FINISH = 2;
    private int threadState = THREAD_INIT;
    
    private threadHandler handler;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        mainLogo = (ImageView)findViewById(R.id.main_logo);
        mainWelcome = (TextView)findViewById(R.id.main_welcome);
        
        Log.v("DiligentPiggy Main", "DiligentPiggy start ...");
        
        
        // 直接用mainLogo.setAlpha()的方式已經不建議使用
        mainLogoDrawable = getResources().getDrawable(R.drawable.logo);        
        mainLogoDrawable.setAlpha(logoAlpha);
        
        // 初始化控制代碼
        handler = new threadHandler(this);
        
        // 開啟新執行緒
        new Thread(new Runnable() {

            @Override
            public void run() {
                initApp(); //初始化程式
                
                // 如果不是結束狀態一直執行
                while(threadState < THREAD_FINISH) {
                    try {
                        if(threadState == THREAD_INIT) {
                            Thread.sleep(2000);
                            threadState = THREAD_RUN;
                        } else {
                            Thread.sleep(50);
                        }
                        updateApp();
                    } catch(InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            
        }).start();
        
    }
    
    public void updateLogoAlpha() {
        mainLogoDrawable.setAlpha(logoAlpha);
        mainLogo.invalidate();        
    }
    
    public void startNextActivity() {
        Log.v("DiligentPiggy Main", "DiligentPiggy start next activity");   
        mainWelcome.setText("DiligentPiggy start next activity");
    }
    
    static class threadHandler extends Handler {
        private WeakReference<MainActivity> mainReference;
        
        public threadHandler(MainActivity activity) {
            mainReference = new WeakReference<MainActivity>(activity);
        }
        
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            MainActivity main = mainReference.get();
            // 更新alpha
            switch(msg.what) {
                case MainActivity.UPDATE_ALPHA:
                    main.updateLogoAlpha();
                    break;
                case MainActivity.START_ACTIVITY:
                    main.startNextActivity();
                    break;
            }                   
        }
    }
    
    public void updateApp() {
        logoAlpha -= 5;
        
        if(logoAlpha <= 0) {
            threadState = THREAD_FINISH;
            handler.sendEmptyMessage(START_ACTIVITY);
        } else {
            handler.sendEmptyMessage(UPDATE_ALPHA);
        }
        
    }
    
    public void initApp() {
        Log.v("DiligentPiggy Main", "DiligentPiggy init ...");
    }

}