Android gallery畫廊

1.xml佈局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <Gallery
        android:id="@+id/gallery"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="30dp" >
    </Gallery>

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:layout_gravity="center_horizontal"
        android:scaleType="fitCenter" />

</LinearLayout>

2.attrs.xml自定義屬性文件：

<?xml version="1.0" encoding="utf-8"?>
<resources>
	<declare-styleable name="Gallery">
		<attr name="android:galleryItemBackground"></attr>
	</declare-styleable>
</resources>

3.java代碼，通過適配器將圖片放入gallery中顯示並添加監聽事件：

package com.android.mygallery;

import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;

public class Main extends Activity {
	/** Called when the activity is first created. */
	private Gallery gallery;
	private ImageAdapter imageAdapter;
	private ImageView imageView;
	// 聲明圖片的數組
	private int[] resIds = { R.drawable.item1, R.drawable.item2,
			R.drawable.item3, R.drawable.item4, R.drawable.item5,
			R.drawable.item6, R.drawable.item7, R.drawable.item8,
			R.drawable.item9, R.drawable.item10, R.drawable.item11,
			R.drawable.item12, R.drawable.item13, R.drawable.item14,
			R.drawable.item15 };

	// android的適配器
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		gallery = (Gallery) this.findViewById(R.id.gallery);
		imageView = (ImageView) findViewById(R.id.imageView);
		imageAdapter = new ImageAdapter(this);
		gallery.setAdapter(imageAdapter);
		//給畫廊設置監聽事件
		gallery.setOnItemClickListener(new OnItemClickListener() {

			@Override
			public void onItemClick(AdapterView<?> parent, View view, int position,
					long id) {
				// TODO Auto-generated method stub
//				Toast.makeText(Main.this, "" + position,   
//                        Toast.LENGTH_LONG).show();   
//				imageView.setImageResource(resIds[position%resIds.length]);
//				imageView.setBackgroundResource((int) id);
			}
		});
		gallery.setOnItemSelectedListener(new OnItemSelectedListener() {

			@Override
			public void onItemSelected(AdapterView<?> parent, View view,
					int position, long id) {
				// TODO Auto-generated method stub
				imageView.setImageResource(resIds[position%resIds.length]);
			}

			@Override
			public void onNothingSelected(AdapterView<?> arg0) {
				// TODO Auto-generated method stub
				
			}
		});
	}

	public class ImageAdapter extends BaseAdapter {

		private Context context;
		int mGralleyItemBackground;// 使用簡單的計數器，填充背景圖片

		public ImageAdapter(Context context) {
			this.context = context;
			// 讀取屬性
			TypedArray typedArray = obtainStyledAttributes(R.styleable.Gallery);
			mGralleyItemBackground = typedArray.getResourceId(
					R.styleable.Gallery_android_galleryItemBackground, 5);

		}

		@Override
		public int getCount() {
			// TODO Auto-generated method stub
			return Integer.MAX_VALUE;
		}

		@Override
		public Object getItem(int position) {
			// TODO Auto-generated method stub
			return resIds[position];
		}

		@Override
		public long getItemId(int position) {
			// TODO Auto-generated method stub
			return position;
		}

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			// TODO Auto-generated method stub
			// 自定義的適配器，需要用自定義的佈局來顯示，通常android的通用佈局是不能滿足我們的需求
			// 可以手工創建一個View視圖，也可以inflate填充一個XML
			// 從數據源中根據position 獲得每一個Item的值，填充到指定的XML佈局中
			// View convertView 是一箇舊的佈局，如果沒有新的佈局填充的時候，將使用舊的佈局
			// 當前的佈局，會被追加到父佈局中
			ImageView imageView = new ImageView(context);
			imageView.setImageResource(resIds[position % resIds.length]);
			imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
			imageView.setLayoutParams(new Gallery.LayoutParams(200, 150));
			imageView.setBackgroundResource(mGralleyItemBackground);
			return imageView;
		}

	}
}

4.問題？：

①自定義屬性是如何在java代碼中使用的？

②typedArray.getResourceId(R.styleable.Gallery_android_galleryItemBackground, 5);  的返回值是什麼？5是defaultValue，之前並沒有對galleryItemBackground賦值，所以其返回值是什麼？從哪裏來？

③setBackgroundResource() 與setImageResource()的區別？

setBackgroundResource是從類 android.view.View 繼承的方法

setImageResource

它們的原型如下：
void android.widget.ImageView.setImageResource(int resId)
void android.view.View.setBackgroundResource(int resid)
區別是：
setImageResource與xml中的src的屬性纔是相匹配的，而setBackgroundResource是與xml中的background屬性相匹配的。

④適配器的使用？