Android 开发第二天

IDE：Android Studio 3.5 RC 2

开发语言：Java

SDK版本：Android 9.0 API 28

builde.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.1"


    defaultConfig {
        applicationId "com.aaa.aListView"
        minSdkVersion 24
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

1. ListView实现数据的列表显示

com.aaa.domain/Dog.java

package com.aaa.domain;

/**
 * 作者：kevin on 2019/8/8 20:19
 */
public class Dog {
    private Integer dogId;      // 狗的编号
    private String dogName;     // 狗的名称
    private String dogSkin;     // 狗的皮肤
    private Float dogPrice;     // 狗的价格

    public Dog() {
    }

    public Dog(String dogName, String dogSkin, Float dogPrice) {
        this.dogName = dogName;
        this.dogSkin = dogSkin;
        this.dogPrice = dogPrice;
    }

    public Dog(Integer dogId, String dogName, String dogSkin, Float dogPrice) {
        this.dogId = dogId;
        this.dogName = dogName;
        this.dogSkin = dogSkin;
        this.dogPrice = dogPrice;
    }

    public Integer getDogId() {
        return dogId;
    }

    public void setDogId(Integer dogId) {
        this.dogId = dogId;
    }

    public String getDogName() {
        return dogName;
    }

    public void setDogName(String dogName) {
        this.dogName = dogName;
    }

    public String getDogSkin() {
        return dogSkin;
    }

    public void setDogSkin(String dogSkin) {
        this.dogSkin = dogSkin;
    }

    public Float getDogPrice() {
        return dogPrice;
    }

    public void setDogPrice(Float dogPrice) {
        this.dogPrice = dogPrice;
    }

    @Override
    public String toString() {
        return "Dog{" +
                "dogId=" + dogId +
                ", dogName='" + dogName + '\'' +
                ", dogSkin='" + dogSkin + '\'' +
                ", dogPrice=" + dogPrice +
                '}';
    }
}

com.aaa.service/OpenDatabaseService.java

package com.aaa.service;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * 作者：kevin on 2019/8/8 17:28
 */
public class OpenDatabaseService extends SQLiteOpenHelper {
    public OpenDatabaseService(Context context) {
        // 参数说明：上下文对象 数据库文件 使用默认游标 数据库版本
        super(context,"kevin.db",null,1);
    }
    // 2019年8月8日17:30:17 这个方法在数据库文件第一次创建的时候被调用
    @Override
    public void onCreate(SQLiteDatabase db) {
        // SQLite数据库中，除了表的主键。其他字段的值是不分类型的，VARCHAR(20)这些东西可以省略
        String sql = "CREATE TABLE dog(dogId integer PRIMARY KEY AUTOINCREMENT,dogName varchar(20),dogSkin varchar(20),dogPrice float(20))";        // 创建表的语句
        db.execSQL(sql);
    }

    @Override   // 2019年8月8日17:38:32 这个方法在数据库版本号发生改变的时候被调用
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }
}

com.aaa.service/DogService.java

package com.aaa.service;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.aaa.domain.Dog;

import java.util.ArrayList;
import java.util.List;

/**
 * 作者：kevin on 2019/8/8 20:53
 */
public class DogService {
    private SQLiteDatabase dbOption;

    public DogService(SQLiteDatabase dbOption) {
        this.dbOption = dbOption;
    }

    // 2019年8月8日20:53:53 插入数据
    public void insert(Dog dog){
        String sql = "INSERT INTO dog(dogName,dogSkin,dogPrice) values(?,?,?)";
        dbOption.execSQL(sql,new Object[]{dog.getDogName(),dog.getDogSkin(),dog.getDogPrice()});
        // dbOption.close();   // 可以关也可以不关
    }
    // 2019年8月8日21:18:58 删除数据
    public void delete(int id){
        String sql = "DELETE FROM dog Where dogId = ?";
        dbOption.execSQL(sql,new Object[]{id});
    }
    // 2019年8月8日21:20:39 改数据
    public void update(Dog dog){
        String sql = "UPDATE dog SET dogName = ?,dogSkin = ?,dogPrice = ? WHERE dogId = ?";
        dbOption.execSQL(sql,new Object[]{dog.getDogName(),dog.getDogSkin(),dog.getDogPrice(),dog.getDogId()});
    }
    // 2019年8月8日21:23:26 查询数据
    public Dog query(int id){
        String sql = "SELECT * FROM dog WHERE dogId = ?";
        Cursor cursor = dbOption.rawQuery(sql, new String[]{String.valueOf(id)});
        if(cursor.moveToFirst()){
            int dogId = cursor.getInt(cursor.getColumnIndex("dogId"));
            String dogName = cursor.getString(cursor.getColumnIndex("dogName"));
            String dogSkin = cursor.getString(cursor.getColumnIndex("dogSkin"));
            float dogPrice = cursor.getFloat(cursor.getColumnIndex("dogPrice"));
            return new Dog(dogId,dogName,dogSkin,dogPrice);
        }
        cursor.close();
        return null;
    }
    // 2019年8月8日21:25:16 获取数据库记录的总条目数
    public long getCount(){
        String sql = "SELECT COUNT(*) FROM dog";
        Cursor cursor = dbOption.rawQuery(sql,null);
        cursor.moveToFirst();
        long result = cursor.getLong(0);
        return result;
    }

    // 2019年8月8日21:39:01 分页查询
    public List<Dog> getPaginationData(int start,int pageSize){
        List<Dog> dogs = new ArrayList<>();
        String sql = "SELECT * FROM dog ORDER BY dogId ASC LIMIT ?,?";
        Cursor cursor = dbOption.rawQuery(sql,new String[]{String.valueOf(start),String.valueOf(pageSize)});
        while (cursor.moveToNext()){
            int dogId = cursor.getInt(cursor.getColumnIndex("dogId"));
            String dogName = cursor.getString(cursor.getColumnIndex("dogName"));
            String dogSkin = cursor.getString(cursor.getColumnIndex("dogSkin"));
            float dogPrice = cursor.getFloat(cursor.getColumnIndex("dogPrice"));
            dogs.add(new Dog(dogId,dogName,dogSkin,dogPrice));
        }
        return dogs;
    }
    // 2019年8月9日08:52:15    获取分页数据的第二种方式
    public Cursor getCursorPagination(int start,int pageSize){
        List<Dog> dogs = new ArrayList<>();
        String sql = "SELECT dogId as _id,dogName,dogSkin,dogPrice FROM dog ORDER BY dogId ASC LIMIT ?,?";
        Cursor cursor = dbOption.rawQuery(sql,new String[]{String.valueOf(start),String.valueOf(pageSize)});
        return cursor;
    }
}

com.aaa.aListView/Main.java

package com.aaa.aListView;

import androidx.appcompat.app.AppCompatActivity;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.SimpleCursorAdapter;

import com.aaa.domain.Dog;
import com.aaa.service.DogService;
import com.aaa.service.OpenDatabaseService;

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

public class Main extends AppCompatActivity {
    private ListView listView;
    private SQLiteDatabase dbOption;
    private DogService dogService;
    private Dog dog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        listView = this.findViewById(R.id.list_item);
        dbOption = new OpenDatabaseService(Main.this).getWritableDatabase();    // 得到数据库操作对象
        dogService = new DogService(dbOption);                                  // 得到dogService对象
        dog = new Dog();
        // insertData();    // 插入假数据40条
        //  showData1();      // 通过SimpleAdapter适配器绑定数据
        // showData2();
        showData3();        // 自定义适配器
    }
    // 2019年8月9日08:39:38 插入假数据，方便后面查询
    public void insertData(){
        for(int i=0; i<40; i++){
            dog.setDogId(i);
            dog.setDogName("阿拉斯加犬"+i+"号");
            dog.setDogSkin("绿色"+i+"号");
            dog.setDogPrice((float)i+100);
            dogService.insert(dog);
        }
    }
    // 2019年8月9日08:48:48    使用SimpleAdapter绑定数据
    public void showData1(){
        List<Dog> dogs = dogService.getPaginationData(5, 20);
        List<HashMap<String,Object>> data = new ArrayList<HashMap<String, Object>>();
        for(Dog dog:dogs){
            HashMap<String,Object> map = new HashMap<String,Object>();
            map.put("dogId",dog.getDogId());
            map.put("dogName",dog.getDogName());
            map.put("dogSkin",dog.getDogSkin());
            map.put("dogPrice",dog.getDogPrice());
            data.add(map);
        }
        // 通过适配器把dogs集合中的数据显示到ListView中的条目
        String[] keys = {"dogId","dogName","dogSkin","dogPrice"};       // data集合中的dogId可以对应的值绑定到R.id.dogId这个控件
        int[] views ={R.id.dogId,R.id.dogName,R.id.dogSkin,R.id.dogPrice};
        SimpleAdapter simpleAdapter = new SimpleAdapter(Main.this,data,R.layout.dogs,keys,views);
        listView.setAdapter(simpleAdapter);
    }
        // 2019年8月9日09:16:54    通过cursor对象绑定数据
    public void showData2(){
        Cursor cursor = dogService.getCursorPagination(5, 20);
        String[] keys = {"_id","dogName","dogSkin","dogPrice"};       // data集合中的dogId可以对应的值绑定到R.id.dogId这个控件
        int[] views ={R.id.dogId,R.id.dogName,R.id.dogSkin,R.id.dogPrice};
        SimpleCursorAdapter simpleCursorAdapter = new SimpleCursorAdapter(Main.this,R.layout.dogs,cursor,keys,views,0);
        listView.setAdapter(simpleCursorAdapter);
    }
   
}

自定义适配器实现数据的绑定

com.aaa.adapter/MyAdapter.java

package com.aaa.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.aaa.aListView.R;
import com.aaa.domain.Dog;

import java.util.List;

/**
 * 作者：kevin on 2019/8/9 09:30
 */
public class MyAdapter extends BaseAdapter {
    private List<Dog> dogs ;    // 定义需要绑定的数据
    private int resource;       // 数据绑定的条目界面
    private LayoutInflater inflater;// 布局填充器，可以用一个xml文件生成一个View对象
    public MyAdapter(Context context, List<Dog> dogs, int resource) {
        this.dogs = dogs;
        this.resource = resource;
        inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override   // 用于得到记录的总数
    public int getCount() {
        return dogs.size(); // 数据的总数
    }

    @Override   // 某个索引对应的元素
    public Object getItem(int position) {
        return dogs.get(position);
    }

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

    @Override   // position 该条目索要绑定的数据在集合中的索引值
    public View getView(int position, View view, ViewGroup parent) {
       if(view == null){
            view = inflater.inflate(resource,null);
       }
       TextView dogId = view.findViewById(R.id.dogId);
        TextView dogName = view.findViewById(R.id.dogName);
        TextView dogSkin = view.findViewById(R.id.dogSkin);
        TextView dogPrice = view.findViewById(R.id.dogPrice);
        Dog dog = dogs.get(position);
        dogId.setText(dog.getDogId());
        dogName.setText(dog.getDogName());
        dogSkin.setText(dog.getDogSkin());
        dogPrice.setText(dog.getDogPrice().toString());
       return view;
    }
}

Main.java添加方法

    // 2019年8月9日09:29:29   通过自定义适配器绑定数据
    public void showData3(){
        List<Dog> dogs = dogService.getPaginationData(5, 20);
        MyAdapter myAdapter = new MyAdapter(Main.this,dogs,R.layout.dogs);
        listView.setAdapter(myAdapter);
    }