Android之AdapterViewFlipper與Gallery

AdapterViewFlipper與Gallery都可以用來展示圖片，但是Gallery是一次性把所有圖片都預加載到屏幕上，而AdapterViewFlipper一次只加載一張圖片。

首先來看看Gallery：

<Gallery 
	    android:id="@+id/gallery"
	    android:layout_width="match_parent"
	    android:layout_height="wrap_content"
	    android:spacing="20dp"    //指定每張圖片之間的間距
	    android:unselectedAlpha="0.4"//指定未選中的圖片透明度爲0.4
	    />

對應的Java代碼：

package org.zqy.andr;

import android.os.Bundle;
import android.os.Handler;
import android.os.Handler.Callback;
import android.os.Message;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;
import android.app.Activity;

public class GalleryActivity extends Activity implements Callback{

	private int[] imageids = { R.drawable.baiyang, R.drawable.jinniu,
			R.drawable.chunv, R.drawable.mojie, R.drawable.shuangzi };
	
	private Gallery gallery;
	private Handler handler;//消息處理的函數
	private int currentIndex = 0;//記錄當前索引
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_gallery);
		
		handler = new Handler(GalleryActivity.this);//初始化一個消息回調函數

		gallery = (Gallery) findViewById(R.id.gallery);//得到Gallery
		gallery.setAdapter(galleryAdapter);//設置適配器
		
		handler.sendEmptyMessage(1);//發送一個空消息，加入到消息隊列
		//停止循環
		//handler.removeMessages(1);
	}

	private BaseAdapter galleryAdapter = new BaseAdapter() {
		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			ImageView imageview = new ImageView(getApplicationContext());
			imageview.setImageResource(imageids[position % imageids.length]);
			imageview.setScaleType(ScaleType.FIT_XY);
			imageview.setLayoutParams(new Gallery.LayoutParams(80, 160));
			return imageview;
		}

		@Override
		public long getItemId(int position) {
			return imageids[position % imageids.length];

		}

		@Override
		public Object getItem(int position) {
			return imageids[position % imageids.length];
		}

		@Override
		public int getCount() {
			return Integer.MAX_VALUE;
		}
	};

	@Override
	public boolean handleMessage(Message msg) {
		gallery.setSelection(currentIndex);
		++currentIndex;
		handler.sendEmptyMessageDelayed(1, 3000);//延遲3s發送一個空消息
		return false;
	}

}

以上寫法可以使得圖片無限自動循環顯示。

再來看看AdapterViewFlipper：

<?xml version="1.0" encoding="utf-8"?>
<AdapterViewFlipper xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/flipper"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:flipInterval="2000">
    
</AdapterViewFlipper>

對應的Java代碼：

package org.zqy.andr;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.AdapterViewFlipper;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

public class Filpper extends Activity {

	private int[] imageids = { R.drawable.baiyang, R.drawable.jinniu,
			R.drawable.chunv, R.drawable.mojie, R.drawable.shuangzi };

	private Animation anim;//定義一個動畫

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.flipper);

		AdapterViewFlipper filpper = (AdapterViewFlipper) findViewById(R.id.flipper);//得到AdapterViewFlipper
		filpper.setAdapter(adapter);//設置一個適配器
		// 開始切換
		filpper.startFlipping();
		anim = AnimationUtils.loadAnimation(getApplicationContext(),
				R.anim.alpha);//初始化動畫

	}

	private BaseAdapter adapter = new BaseAdapter() {

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			ImageView imageview = new ImageView(getApplicationContext());
			imageview.setImageResource(imageids[position]);
			imageview.setScaleType(ScaleType.FIT_XY);
			imageview.setLayoutParams(new AdapterViewFlipper.LayoutParams(480,
					500));
			imageview.setAnimation(anim);//加載動畫
			return imageview;
		}

		@Override
		public long getItemId(int position) {
			return imageids[position];

		}

		@Override
		public Object getItem(int position) {
			return imageids[position];
		}

		@Override
		public int getCount() {
			return imageids.length;
		}
	};

}

以上代碼用到了動畫的知識，在res文件夾下新建一個anim文件夾，在其裏面新建一個alpha.xml文件

<?xml version="1.0" encoding="utf-8"?>
<alpha
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromAlpha="0.0"//指定初始透明度
    android:toAlpha="1.0"
    android:duration="4000">//申明切換時間
    
</alpha>

總結：AdapterViewFlipper與Gallery各有各的優勢，視具體使用場景而定。