Android學習筆記（六）——自定義ListView佈局+AsyncTask異步任務

本次的案例實現如下的水果列表：當下拉列表的時候，出現正在加載數據，然後並顯示下一組數據。點擊對應的購物車圖標，則會顯示XXX已加入購物車！

實現代碼如下：
FruitItim.java

package cn.edu.hznu.ex5_0.bean;
public class FruitItem {
    private int  fruitImageId;
    private String fruitName;
    private double fruitPrice;
    private int carImageId;
    public FruitItem() {
    }
    public FruitItem(int fruitImageId, String fruitName, double fruitPrice, int carImageId) {
        this.fruitImageId = fruitImageId;
        this.fruitName = fruitName;
        this.fruitPrice = fruitPrice;
        this.carImageId = carImageId;
    }
    public int getFruitImageId() {
        return fruitImageId;
    }

    public void setFruitImageId(int fruitImageId) {
        this.fruitImageId = fruitImageId;
    }

    public String getFruitName() {
        return fruitName;
    }

    public void setFruitName(String fruitName) {
        this.fruitName = fruitName;
    }

    public double getFruitPrice() {
        return fruitPrice;
    }

    public void setFruitPrice(double fruitPrice) {
        this.fruitPrice = fruitPrice;
    }

    public int getCarImageId() {
        return carImageId;
    }

    public void setCarImageId(int carImageId) {
        this.carImageId = carImageId;
    }
}

FruitResource.java

package cn.edu.hznu.ex5_0.bean;
import cn.edu.hznu.ex5_0.R;
/**
 * Created by b on 2019/3/17.
 */
public class FruitResource {
    public static int[] fruitImageIds={R.drawable.apple_pic, R.drawable.banana_pic,
            R.drawable.cherry_pic,R.drawable.grape_pic,R.drawable.mango_pic, R.drawable.orange_pic,
            R.drawable.pear_pic, R.drawable.pineapple_pic,R.drawable.strawberry_pic,R.drawable.watermelon_pic
            };
    public static String[] friutNames={"apple","banana","cherry","grape","mango",
    "orange","pear","pineapple","strawberry","watermelon"};
}

FruitAdapter.java

package cn.edu.hznu.ex5_0.adapter;
import android.content.Context;
import android.support.annotation.NonNull;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.List;
import cn.edu.hznu.ex5_0.R;
import cn.edu.hznu.ex5_0.bean.FruitItem;
public class FruitAdapter extends ArrayAdapter <FruitItem> {
    //列表項佈局的id
    private int item_layout_id;
    public FruitAdapter(Context context, int resource, List objects) {
        super(context, resource,objects);
        item_layout_id=resource;
    }
    /**
     * getView()方法：在加載每一個的時候被調用
     * position:當次需要加載（顯示）列表項的位置
     * convertView:回收站，重複利用的子視圖
     * @param position
     * @param convertView
     * @param parent
     * @return  返回的是加載的這個列表項的子視圖
     */
    @NonNull
    @Override
    public View getView(int position, View convertView, final ViewGroup parent) {
        View view=null;  //當前列表項的子視圖
        ViewHolder  holder;
        if(convertView==null){//回收站爲空\
            /**
             * LayoutInflater.from()得到佈局填充器對象
             * getContext()獲取當前上下文
             * inflate() 加載填充佈局
             */
          view= LayoutInflater.from(getContext())
                  .inflate(item_layout_id,parent,false);
          holder=new ViewHolder(view);
          view.setTag(holder);

        }else {//顯示後續的列表項
            view=convertView;
            holder= (ViewHolder) view.getTag();
        }
        final FruitItem itemData=getItem(position);
        holder.fruitImage.setImageResource(itemData.getFruitImageId());
        holder.fruitName.setText(itemData.getFruitName());
        holder.fruitPrice.setText(itemData.getFruitPrice()+"元/kg");
        holder.carImage.setImageResource(itemData.getCarImageId());
        holder.carImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(parent.getContext(),itemData.getFruitName()+ "已加入購物車！", Toast.LENGTH_SHORT).show();
            }
        });
        return view;
    }
    class  ViewHolder{
        ImageView  fruitImage;
        TextView  fruitName;
        TextView  fruitPrice;
        ImageView  carImage;
      public ViewHolder(View view){
            fruitImage= (ImageView) view.findViewById(R.id.fruitImage);
            fruitName= (TextView) view.findViewById(R.id.fruitName);
            fruitPrice= (TextView) view.findViewById(R.id.fruitPrice);
            carImage= (ImageView) view.findViewById(R.id.carImage);
        }
    }
}

FruitTask.java

package cn.edu.hznu.ex5_0.task;
import android.os.AsyncTask;
import java.util.ArrayList;
import cn.edu.hznu.ex5_0.R;
import cn.edu.hznu.ex5_0.bean.FruitItem;
import cn.edu.hznu.ex5_0.bean.FruitResource;
//異常任務中幾個方法的執行順序：onPreExecute()->doInBackground()->onPostExecute()
/**
 * Created by 2017810402084 on 2020-04-09.
 *  三個泛型：1、第一個泛型的類型根據異步任務執行時傳的參數類型
 * 2、如果執行異步任務時，需要同步顯示相應的進度，則設爲Int
 * 3、第二個泛型的類型根據異步任務執行結束後結果的類型
 */
public class FruitTask extends  AsyncTask<Integer,Void,ArrayList<FruitItem>> {

    //4\添加一個屬性
    private  CallBack back;
//5、構造方法
    public FruitTask(CallBack back) {
        this.back = back;
    }

    @Override
    protected void onPreExecute() {
        //在主線程執行
        super.onPreExecute();
    }
    @Override
    protected void onProgressUpdate(Void... values) {
        //做進度顯示的操作
        super.onProgressUpdate(values);
    }

    @Override
    protected ArrayList<FruitItem> doInBackground(Integer... integers) {
        //Integer... integers 可變參數
        //在子線程中執行
        ArrayList<FruitItem> data=new ArrayList<>();
        for(int i = 0; i< FruitResource.friutNames.length; i++){
            double price=5+((int)(Math.random()*100))/10.0;
            FruitItem itemData=new FruitItem( FruitResource.fruitImageIds[i], FruitResource.friutNames[i]+":"+integers[0],price, R.drawable.shopping_car);
            data.add(itemData);
        }
        try{
            Thread.sleep(2000);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        return data;
    }
    @Override
    protected void onPostExecute(ArrayList<FruitItem> result) {
        //在主線程中執行
        if(back!=null)
            back.getResult(result);
       super.onPostExecute(result);

    }
    public interface CallBack{
        void getResult(ArrayList<FruitItem> result);  //第三個參數是什麼類型就是什麼類型
    }
}

MainActivity.java

package cn.edu.hznu.ex5_0;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import cn.edu.hznu.ex5_0.adapter.FruitAdapter;
import cn.edu.hznu.ex5_0.bean.FruitItem;
import cn.edu.hznu.ex5_0.task.FruitTask;
public class MainActivity extends AppCompatActivity {
    private ListView listView;  //定義listview
    private ArrayList<FruitItem> data=new ArrayList<>();
    private FruitAdapter adapter;
    private boolean isLoading=true,isDown=false;
    private int curPage=1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView= (ListView) findViewById(R.id.listView);  //綁定
        //**********************添加帶有底部視圖**************************************
        View view= LayoutInflater.from(this).inflate(R.layout.footer_layout,null);
        listView.addFooterView(view);

        loadData();   //將列表項的數據加載到數據源（順序表）中
        adapter=new FruitAdapter(MainActivity.this, R.layout.item_layout,data);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, "你選擇的水果是："+data.get(position).getFruitName(), Toast.LENGTH_SHORT).show();
            }
        });


          //添加列表的滾動事件
        listView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView absListView, int scrollState) {
                if(isDown==true&&scrollState==SCROLL_STATE_IDLE){
                    loadData();
                }
            }

            @Override
            public void onScroll(AbsListView absListView, int i, int i1, int i2) {
                if(i+i1==i2){
                    isDown=true;
                }else{
                    isDown=false;
                }
            }
        });

    }
    private void loadData() {
        if(isLoading){
            isLoading=false;
            new FruitTask(new FruitTask.CallBack() {
                @Override
                public void getResult(ArrayList<FruitItem> result) {//重寫接接口方法
                    data.addAll(result);
                    adapter.notifyDataSetChanged();
                }
            }).execute(curPage);
            isLoading=true;
            curPage++;
        }
    }
    }

佈局文件
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cn.edu.hznu.ex5_0.MainActivity">
   <ListView
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:id="@+id/listView">
   </ListView>
</RelativeLayout>

footer_layout.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="wrap_content">
    <ProgressBar
        style="?android:attr/progressBarStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/progressBar"
        android:layout_weight="1" />

    <TextView
        android:text="正在加載數據........"
        android:textSize="24sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/textView"
        android:layout_weight="1" />
</LinearLayout>

item_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="match_parent">
<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/apple_pic"
    android:id="@+id/fruitImage"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="蘋果"
            android:textSize="28sp"
            android:gravity="center"
            android:id="@+id/fruitName"/>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">
            <TextView
                android:layout_width="0dp"
                android:layout_weight="4"
                android:layout_height="wrap_content"
                android:text="12.8元/kg"
                android:textSize="28sp"
                android:gravity="center"
                android:id="@+id/fruitPrice"/>
            <ImageView
                android:layout_width="0dp"
                android:layout_weight="1"
                android:layout_height="match_parent"
                android:src="@drawable/shopping_car"
                android:id="@+id/carImage"
               />
        </LinearLayout>
    </LinearLayout>
</LinearLayout>

另外需要10張水果圖片需要放在項目的drawable文件夾下！！！

                                                             2020-04-09   Android 學習的第六課