ssdAndroid 測試說明BaseAdapter的使用, ListView, List, Map, viewHolder

BaseAdapterDemo.java

package com.example.administrator.test;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Created by Administrator on 2014/10/13.
 */
public class BaseAdapterDemo extends Activity {
    private ListView lv;
    public List<Map<String, Object>> data;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        lv = (ListView) findViewById(R.id.lv);

        /* 獲取將要綁定的數據, 存入data中 */
        data = getData();
        MyAdapter adapter = new MyAdapter(this);
        lv.setAdapter(adapter);

    }

    private List<Map<String, Object>> getData() {
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Map<String, Object> map;

        for (int i = 0 ; i < 10 ; i++) {
            map = new HashMap<String, Object>();
            map.put("img", R.drawable.ic_launcher);
            map.put("title", "肯德基");
            map.put("info", "有這麼好吃嗎???");
            list.add(map);
        }

        return list;
    }

    /* ViewHolder 靜態類 */
    static class ViewHolder {
        public ImageView img;
        public TextView title;
        public TextView info;
    }

    class MyAdapter extends BaseAdapter {
        private LayoutInflater mInflater = null;

        private MyAdapter(Context context) {
            this.mInflater = LayoutInflater.from(context);
        }

        @Override
        public int getCount() {
            return data.size();
        }

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

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder;

            if (convertView == null) {
                holder = new BaseAdapterDemo.ViewHolder();
                convertView = mInflater.inflate(R.layout.list_item, null);
                holder.img = (ImageView) convertView.findViewById(R.id.img);
                holder.title = (TextView) convertView.findViewById(R.id.title);
                holder.info = (TextView) convertView.findViewById(R.id.info);
                convertView.setTag(holder);
            } else {
                holder = (BaseAdapterDemo.ViewHolder) convertView.getTag();
            }

            holder.img.setBackgroundResource((Integer) data.get(position).get("img"));
            holder.title.setText((String) data.get(position).get("title"));
            holder.info.setText((String) data.get(position).get("info"));

            return convertView;
        }
    }
}

list_item.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/img" />

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/tv"
            android:textSize="20sp" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/info"
            android:textSize="14sp" />
    </LinearLayout>
</LinearLayout>

main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/lv"
        android:fastScrollEnabled="true" />
</LinearLayout>

note.text

Adapter(適配器)
適配器對象作為AdapterView之間的一個橋樑，並為這一觀點的基礎數據。適配器提供的數據項的訪問。適配器也作出負責的數據集給每個項目。

簡單的來說就是資料和元件間溝通的橋樑

Adapter有以下幾種間接子類別:
ArrayAdapter
BaseAdapter
CursorAdapter
HeaderViewListAdapter
ListAdapter
ResourceCursorAdapter
SimpleAdapter
SimpleCursorAdapter
SpinnerAdapter
WrapperListAdapter


getCount()
適配器內的資料個數

public int getCount() {
	return title.length;
}


getItem(int position)
在指定位置的數據

public Object getItem(int position) {
	return title[position];
}



getItemId(int position)
獲取的id在顯示的列表中的位置

public long getItemId(int position) {
	return position;
}


/* 獲取有getView(int, 查看, ViewGroup的) 創建的視圖的指定項目 */
getItemViewType(int position) {
	return position;
}



getView(int position, View convertView, ViewGroup parent)



public View getView(int position, View convertView, ViewGroup parent) {
	/* 自定義類別, 表達個別listItem中的view物件集合 */
	ViewTag viewTag;	

	if(convertView == null) {
		//取得listItem容器 view
		convertView = myInflater.inflate(R.layout.adapter, null);

		//建構listItem內容view
		viewTag = new ViewTag(
			(ImageView) convertView.findViewById(R.id.MyAdapter_ImageView_icon),
			(TextView) converView.findViewById(R.id.MyAdapter_TextView_title),
			(TextView) convertView.findViewById(R.id.MyAdapter_TextView_info)
		);

		//設置容器內容
		convertView.setTag(viewTag);
	} else {
		viewTag = (ViewTag) convertView.getTage();
	}

	//設定內容圖案
	switch(position) {
		case 0:
			viewTag.icon.setBackgroundResource(R.drawable.taipei);
			break;
		case 1:
			viewTag.icon.setBackgroundResource(R.drawable.taichung);
			break;
		case 2:
			viewTag.icon.setBackgroundResource(R.drawable.kaohsiung);
			break;
	}

	//設定標題文字
	viewTag.title.setText(title[position]);
	
	//設定內容文字
	viewTag.info.setText(info[position]);

	return convertView;
}



Adapter(適配器)還蠻常會看到的，因為如果想客製化介面元件的話，一般都需要用到Adapter(適配器)改變元件為自定義形式，
最常用的就是BaseAdapter這個子類，一般形態ArrayAdapter也蠻常用的，不過ArrayAdapter都是用在沒什麼改變時調用，
如果想自定義一般都會做用到BaseAdapter這個子類


BaseAdapter

ListView listView = (ListView) findViewById(R.id.listView1);
CharSequence[] list = MemorandumDate;
CharSequence[] list2 = MemorandumNote;
CharSequence[] list3 = MemorandumPW;
BaseAdapter adapter = new MyAdapter(this, list, mID, list2, list3, mReminder);
listView.setAdapter(adapter);


BaseAdapter与其他Adapter有些不一样，其他的Adapter可以直接在其构造方法中进行数据的设置，比如

SimpleAdapter adapter = new SimpleAdapter(this, getData(), R.layout.list_item, 
	new String[] {"1","2","3"}, new int[] {1, 2, 3});


在BaseAdapter中需要实现一个继承自BaseAdapter的类，并且重写里面的很多方法

class MyAdapter extends BaseAdapter {
	private Context context;
	public MyAdapter(Context context) {
		this.context = context;
	}

	@Override
	public int getCount() {
		return 0;	// 此適配器中所代表的數據的條目數
	}

	@Override
	public Object getItem(int position) {
		return null;	// 獲取索引對應的數據
	}

	@Override
	public long getItemId(int position) {
		return 0;	// 取得列表中數據對應的id
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		return null;	//最重要的View
	}
}

--------------------------------------------
關於getView()的處理, 重點說明

以下為寫法1, 沒有任何處理, 非常不推薦, 很影響效能 (因為每次都要創建View)

@Override
public View getView(int position, View convertView, ViewGroup parent) {
	View item = mInflater.inflate(R.layout.list_item, null);
	ImageView img = (ImageView) item.findViewById(R.id.img);
	TextView info = (TextView) item.findViewById(R.id.info);
	img.setImageResource(R.drawable.ic_launcher);
	info.setText("world");

	return item;
}


以下為寫法2, 通過緩存convertView, 判斷緩存中不存在View, 才創建View, 如果存在View, 那就直接利用, 藉以提升性能


@Override
public View getView(int position, View convertView, ViewGroup parent) {
	if(convertView == null) {
		convertView = mInflater.inflate(R.layout.list_item, null);
	}

	ImageView img = (ImageView) convertView.findViewById(R.id.img);
	TextView info = (TextView) vonvertView.findViewById(R.id.info);
	img.setImageResource(R.drawable.ic_launcher);
	info.setText("world");

	return convertView;
}


以下為寫法3, 通過convertView + ViewHolder來實現, 
ViewHolder是一個靜態類, 使用ViewHolder的關鍵好處, 就是緩存了顯示數據的View, 加快了UI的響應速度
當判斷convertView == null時, 系統就是根據設計好的List的布局, 來給convertView賦值,
並生成一個viewHolder來綁定convertView裡面的各個View控件
再用convertView的setTag, 將viewHolder設置到Tag中
以便系統第2次繪製ListView時, 從Tag中取出


/* 先定義好ViewHolder靜態類 */
{
	public ImageView img;
	public TextView info;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
	ViewHolder holder;
	
	if(convertView == null) {
		holder = new ViewHolder();
		convertView = mInflater.inflate(R.layout.list_item, null);
		ImageView img = (ImageView) item.findViewById(R.id.img);
		TextView info = (TextView) item.findViewById(R.id.info);
		convertView.setTag(holder);
	} else {
		holder = (ViewHolder) convertView.getTag();
		holder.img.setImageResource(R.drawable.ic_launcher);
		holder.info.setText("world");
	}

	return convertView;
}


ViewHolder模式通过getView()方法返回的视图的标签(Tag)中存储一个数据结构，
这个数据结构包含了指向我们要绑定数据的视图的引用，从而避免每次调用getView()的时候调用findViewById()