Android-Room，RecyclerView，CardView的简单使用以及数据迁移

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我是靠谱客的博主活泼月光，最近开发中收集的这篇文章主要介绍Android-Room，RecyclerView，CardView的简单使用以及数据迁移，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

文章目录

- Room
- - 介绍和依赖
  - 简单案列
  - 代码优化
  - RecyclerView
  - CardView，波纹效果和网页跳转
  - 增加隐藏
  - 数据迁移
  - - 破坏式迁移
    - SQL语句方式(※)

Room

介绍和依赖

官网地址： https://developer.android.google.cn/jetpack/androidx/releases/room

def room_version = "2.2.5"

    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"

//    // optional - RxJava support for Room
//    implementation "androidx.room:room-rxjava2:$room_version"
//
//    // optional - Guava support for Room, including Optional and ListenableFuture
//    implementation "androidx.room:room-guava:$room_version"

    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"

简单案列

导入依赖

def room_version = "2.2.5"

implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
testImplementation "androidx.room:room-testing:$room_version"

编写实体类

package com.example.roombasic;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

/**
 * @author codekiller
 * @date 2020/11/16 17:42
 * @Description TODO
 */
@Entity
public class Word {
    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "english_word")
    private String word;

    @ColumnInfo(name = "chinese_meaning")
    private String chineseMeaning;

    public Word(){}

    public Word(String word, String chineseMeaning) {
        this.word = word;
        this.chineseMeaning = chineseMeaning;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Word setIdc(int id){
        this.id = id;
        return this;
    }

    public String getWord() {
        return word;
    }

    public void setWord(String word) {
        this.word = word;
    }

    public String getChineseMeaning() {
        return chineseMeaning;
    }

    public void setChineseMeaning(String chineseMeaning) {
        this.chineseMeaning = chineseMeaning;
    }
}

编写数据库操作Dao类

package com.example.roombasic;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

/**
 * @author codekiller
 * @date 2020/11/16 17:44
 * @Description Dao: Database Access Object
 */
@Dao
public interface WordDao {

    @Insert
    void insertWords(Word... words);

    @Update
    void updateWords(Word... words);

    @Delete
    void deleteWords(Word... words);

    @Query("DELETE FROM WORD")
    void deleteAllWords();

    @Query("SELECT * FROM WORD ORDER BY ID DESC")
    List<Word> getAllWords();
}

数据库类

@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    public abstract  WordDao getWordDao();
}

界面

具体的数据库操作

package com.example.roombasic;

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;
import androidx.room.util.StringUtil;

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    WordDatabase wordDatabase;
    WordDao wordDao;

    TextView textView;
    Button insertButton,updateButton,clearButton,deleteButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordDatabase = Room.databaseBuilder(this,WordDatabase.class,"word_database")
            .allowMainThreadQueries()
            .build();

        textView = findViewById(R.id.textView2);
        insertButton = findViewById(R.id.insertButton);
        updateButton = findViewById(R.id.updateButton);
        clearButton = findViewById(R.id.clearButton);
        deleteButton = findViewById(R.id.deleteButton);

        wordDao = wordDatabase.getWordDao();

        updateView();

        //插入操作
        insertButton.setOnClickListener(v->{
            Word word1 = new Word("Hello","你好");
            Word word2 = new Word("World","世界");
            wordDao.insertWords(word1,word2);
            updateView();
        });

        //更新操作
        updateButton.setOnClickListener(v->{
            Word word = new Word("spring","春天");
            word.setId(1);
            wordDao.updateWords(word);
            updateView();
        });

        //清除操作
        clearButton.setOnClickListener(v->{
            wordDao.deleteAllWords();
            updateView();
        });

        //删除操作
        deleteButton.setOnClickListener(v->{
            wordDao.deleteWords(new Word().setIdc(4));
            updateView();
        });



    }

    void updateView(){
        List<Word> words = wordDao.getAllWords();
        String text = "";
        for (int i=words.size()-1;i>=0;--i) {
            text += words.get(i).getId()+"："+words.get(i).getWord()+" = "+words.get(i).getChineseMeaning()+";n";
        }
        textView.setText(text);

    }

}

运行相关操作可以在我们的文件中看到

代码优化

在上面的例子中，我们可以看到，数据库的操作都是放在主线程里面进行执行的，这显然不是太好。而且我们的mainActivity里面代码太多了，现在对代码进行一些修改。

看下文件结构

Word不变
WordDao不变

WordDatabase，采用单例模式

@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    private static WordDatabase INSTANCE;


    /**
    * @Description 单例获取
    * @date 2020/11/17 8:14
    * @param context
    * @return
    */
    public static synchronized WordDatabase getDatabase(Context context){
        if(INSTANCE == null){
            INSTANCE = Room.databaseBuilder(context, WordDatabase.class, "word_database")
                .allowMainThreadQueries()
                .build();
        }
        return INSTANCE;
    }

    public abstract  WordDao getWordDao();
}

WordRepository，封装数据库的操作

public class WordRepository {

    private LiveData<List<Word>> allWordsLive;

    private WordDao wordDao;

    public WordRepository(Context context) {
        WordDatabase wordDatabase = WordDatabase.getDatabase(context);
        wordDao = wordDatabase.getWordDao();
        allWordsLive = wordDao.getAllWords();
    }

    public LiveData<List<Word>> getAllWordsLive() {
        return allWordsLive;
    }

    public void insertWords(Word... words) {
        new InsertAsyncTask(wordDao).doInBackground(words);
    }

    public void updateWords(Word... words) {
        new UpdateAsyncTask(wordDao).doInBackground(words);
    }

    public void deleteWords(Word... words) {
        new DeleteAsyncTask(wordDao).doInBackground(words);
    }

    public void deleteAllWords() {
        new DeleteAllAsyncTask(wordDao).doInBackground();
    }

    static class InsertAsyncTask extends AsyncTask<Word, Void, Void> {

        private WordDao wordDao;

        public InsertAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.insertWords(words);
            return null;
        }
    }

    static class UpdateAsyncTask extends AsyncTask<Word, Void, Void> {

        private WordDao wordDao;

        public UpdateAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.updateWords(words);
            return null;
        }
    }

    static class DeleteAsyncTask extends AsyncTask<Word, Void, Void> {

        private WordDao wordDao;

        public DeleteAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protected Void doInBackground(Word... words) {
            wordDao.deleteWords(words);
            return null;
        }
    }

    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {

        private WordDao wordDao;

        public DeleteAllAsyncTask(WordDao wordDao) {
            this.wordDao = wordDao;
        }

        @Override
        protecteds Void doInBackground(Void... voids) {
            this.wordDao.deleteAllWords();
            return null;
        }
    }
}

注意一点：AsyncTask已经被弃用了

WordViewModel

public class WordVIewModel extends AndroidViewModel {

    private WordRepository wordRepository;

    public WordVIewModel(@NonNull Application application) {
        super(application);
        wordRepository = new WordRepository(application);

    }

    public LiveData<List<Word>> getAllWordsLive() {
        return wordRepository.getAllWordsLive();
    }


    public void insertWords(Word... words) {
        wordRepository.insertWords(words);
    }

    public void updateWords(Word... words) {
        wordRepository.updateWords(words);
    }

    public void deleteWords(Word... words) {
        wordRepository.deleteWords(words);
    }

    public void deleteAllWords() {
        wordRepository.deleteAllWords();
    }
}

MainActivity

public class MainActivity extends AppCompatActivity {


    TextView textView;
    Button insertButton,updateButton,clearButton,deleteButton;

    private WordVIewModel wordVIewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordVIewModel = new ViewModelProvider(this).get(WordVIewModel.class);

        textView = findViewById(R.id.textView2);
        insertButton = findViewById(R.id.insertButton);
        updateButton = findViewById(R.id.updateButton);
        clearButton = findViewById(R.id.clearButton);
        deleteButton = findViewById(R.id.deleteButton);



        wordVIewModel.getAllWordsLive().observe(this,(words)->{
            StringBuilder text = new StringBuilder();
            for (int i=words.size()-1;i>=0;--i) {
                text.append(words.get(i).getId()).append("：").append(words.get(i).getWord()).append(" = ").append(words.get(i).getChineseMeaning()).append(";n");
            }
            textView.setText(text.toString());
        });

        //插入操作
        insertButton.setOnClickListener(v->{
            Word word1 = new Word("Hello","你好");
            Word word2 = new Word("World","世界");
            wordVIewModel.insertWords(word1,word2);
        });

        //更新操作
        updateButton.setOnClickListener(v->{
            Word word = new Word("spring","春天");
            word.setId(1);
            wordVIewModel.updateWords(word);
        });

        //清除操作
        clearButton.setOnClickListener(v->{
            wordVIewModel.deleteAllWords();
        });

        //删除操作
        deleteButton.setOnClickListener(v->{
            wordVIewModel.deleteWords(new Word().setIdc(10));
        });
    }
}

RecyclerView

RecyclerView的优点

进行item回收复用
RecyclerView封装了viewholder的回收复用，也就是说RecyclerView标准化了ViewHolder，编写Adapter面向的是ViewHolder而不再是View了，复用的逻辑被封装了，写起来更加简单。
提供了一种插拔式的体验，高度的解耦，异常的灵活，针对一个Item的显示RecyclerView专门抽取出了相应的类，来控制Item的显示，使其的扩展性非常强。例如：你想控制横向或者纵向滑动列表效果可以通过LinearLayoutManager这个类来进行控制(与GridView效果对应的是GridLayoutManager,与瀑布流对应的还StaggeredGridLayoutManager等)，也就是说RecyclerView不再拘泥于ListView的线性展示方式，它也可以实现GridView的效果等多种效果。你想控制Item的分隔线，可以通过继承RecyclerView的ItemDecoration这个类，然后针对自己的业务需求去抒写代码。
可以控制Item增删的动画，可以通过ItemAnimator这个类进行控制，当然针对增删的动画，RecyclerView有其自己默认的实现。

首先修改一下插入操作代码

insertButton.setOnClickListener(v->{
    String[] english = {
        "Hello",
        "World",
        "Android",
        "Google",
        "Studio",
        "Project",
        "Database",
        "Recycler",
        "View",
        "String",
        "Value",
        "Integer"
    };
    String[] chinese = {
        "你好",
        "世界",
        "安卓系统",
        "谷歌公司",
        "工作室",
        "项目",
        "数据库",
        "回收站",
        "视图",
        "字符串",
        "价值",
        "整数类型"
    };
    for(int i=0;i<chinese.length;i++){
        wordVIewModel.insertWords(new Word(english[i], chinese[i]));
    }
});

使用RecyclerView

创建layout

创建元素的layout

创建一个Adapter

package com.example.roombasic;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
import java.util.List;

/**
 * @author codekiller
 * @date 2020/11/17 9:20
 * @Description TODO
 */
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    List<Word> allWords = new ArrayList<>();

    public void setAllWords(List<Word> allWords){
        this.allWords = allWords;
    }


    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View itemView = layoutInflater.inflate(R.layout.cell_normal,parent,false);
        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        Word word = allWords.get(position);
        holder.textViewNumber.setText(String.valueOf(position+1));
        holder.textViewEnglish.setText(word.getWord());
        holder.textViewChinese.setText(word.getChineseMeaning());
    }

    @Override
    public int getItemCount() {
        return allWords.size();
    }

    static class MyViewHolder extends RecyclerView.ViewHolder{

        TextView textViewNumber, textViewEnglish, textViewChinese;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            textViewNumber = itemView.findViewById(R.id.textViewNumber);
            textViewChinese = itemView.findViewById(R.id.textViewChinese);
            textViewEnglish = itemView.findViewById(R.id.textViewEnglish);

        }
    }

}

修改MainAdapter代码

package com.example.roombasic;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.room.Room;
import androidx.room.util.StringUtil;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import java.util.List;

public class MainActivity extends AppCompatActivity {


    RecyclerView recyclerView;
    Button insertButton,updateButton,clearButton,deleteButton;
    MyAdapter myAdapter;

    private WordVIewModel wordVIewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wordVIewModel = new ViewModelProvider(this).get(WordVIewModel.class);


        insertButton = findViewById(R.id.insertButton);
        updateButton = findViewById(R.id.updateButton);
        clearButton = findViewById(R.id.clearButton);
        deleteButton = findViewById(R.id.deleteButton);

        recyclerView = findViewById(R.id.recyclerView);
        myAdapter = new MyAdapter();

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(myAdapter);

        wordVIewModel.getAllWordsLive().observe(this,(words)->{
            myAdapter.setAllWords(words);
            myAdapter.notifyDataSetChanged();
        });

        //插入操作
        insertButton.setOnClickListener(v->{
            String[] english = {
                "Hello",
                "World",
                "Android",
                "Google",
                "Studio",
                "Project",
                "Database",
                "Recycler",
                "View",
                "String",
                "Value",
                "Integer"
            };
            String[] chinese = {
                "你好",
                "世界",
                "安卓系统",
                "谷歌公司",
                "工作室",
                "项目",
                "数据库",
                "回收站",
                "视图",
                "字符串",
                "价值",
                "整数类型"
            };
            for(int i=0;i<chinese.length;i++){
                wordVIewModel.insertWords(new Word(english[i], chinese[i]));
            }
        });

        //更新操作
        updateButton.setOnClickListener(v->{
            Word word = new Word("spring","春天");
            word.setId(1);
            wordVIewModel.updateWords(word);
        });

        //清除操作
        clearButton.setOnClickListener(v->{
            wordVIewModel.deleteAllWords();
        });

        //删除操作
        deleteButton.setOnClickListener(v->{
            wordVIewModel.deleteWords(new Word().setIdc(10));
        });
    }
}

CardView，波纹效果和网页跳转

创建一个新的layout，记得三个textView的id，和cell_normal中相同的就行

设置一下margin，CardView下修改

修改Adapter

@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
    View itemView = layoutInflater.inflate(R.layout.cell_card,parent,false);
    return new MyViewHolder(itemView);
}

波纹效果

相当于

再修改背景样式

运行之后发现，可点击，但是波纹效果是在后面的，此时要修改一下前景

效果图演示

这里有一个小功能，就是跳转到有道词典了。修改adapter

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
    Word word = allWords.get(position);
    holder.textViewNumber.setText(String.valueOf(position+1));
    holder.textViewEnglish.setText(word.getWord());
    holder.textViewChinese.setText(word.getChineseMeaning());

    holder.itemView.setOnClickListener(v->{
        Uri uri = Uri.parse("https://m.youdao.com/dict?le=eng&q=" + holder.textViewEnglish.getText());
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setData(uri);
        holder.itemView.getContext().startActivity(intent);
    });
}

增加隐藏

增加一个switch

增加一个字段

@ColumnInfo(name = "chinese_invisible")
private boolean chineseInvisible;

修改adapter

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private List<Word> allWords = new ArrayList<>();
    private WordVIewModel wordVIewModel;

    public MyAdapter(WordVIewModel wordVIewModel) {
        this.wordVIewModel = wordVIewModel;
    }

    public void setAllWords(List<Word> allWords){
        this.allWords = allWords;
    }


    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View itemView = layoutInflater.inflate(R.layout.cell_card2,parent,false);
        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        Word word = allWords.get(position);
        holder.textViewNumber.setText(String.valueOf(position+1));
        holder.textViewEnglish.setText(word.getWord());
        holder.textViewChinese.setText(word.getChineseMeaning());

        holder.aSwitchChineseInvisible.setOnCheckedChangeListener(null);

        //控制显示和隐藏中文
        if(word.isChineseInvisible()){
            //GONE 会隐藏，而且会释放空间(改变位置)，而invisible仅仅是不显示。
            holder.textViewChinese.setVisibility(View.GONE);
            holder.aSwitchChineseInvisible.setChecked(true);
        } else {
            holder.textViewChinese.setVisibility(View.VISIBLE);
            holder.aSwitchChineseInvisible.setChecked(false);
        }

        //进行有道词典搜索
        holder.itemView.setOnClickListener(v->{
            Uri uri = Uri.parse("https://m.youdao.com/dict?le=eng&q=" + holder.textViewEnglish.getText());
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setData(uri);
            holder.itemView.getContext().startActivity(intent);
        });

        //switch监听
        holder.aSwitchChineseInvisible.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if(isChecked){
                    holder.textViewChinese.setVisibility(View.GONE);
                    word.setChineseInvisible(true);
                    wordVIewModel.updateWords(word);
                }else{
                    holder.textViewChinese.setVisibility(View.VISIBLE);
                    word.setChineseInvisible(false);
                    wordVIewModel.updateWords(word);
                }

            }
        });
    }

    @Override
    public int getItemCount() {
        return allWords.size();
    }

    static class MyViewHolder extends RecyclerView.ViewHolder{

        TextView textViewNumber, textViewEnglish, textViewChinese;

        Switch aSwitchChineseInvisible;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            textViewNumber = itemView.findViewById(R.id.textViewNumber);
            textViewChinese = itemView.findViewById(R.id.textViewChinese);
            textViewEnglish = itemView.findViewById(R.id.textViewEnglish);
            aSwitchChineseInvisible = itemView.findViewById(R.id.chineseInvisible);
        }
    }

}

这一点尤为重要

holder.aSwitchChineseInvisible.setOnCheckedChangeListener(null);

修改MainActvity

一定要避免两次刷新，不然后卡顿

wordVIewModel.getAllWordsLive().observe(this,(words)->{
    int temp = myAdapter.getItemCount();
    myAdapter.setAllWords(words);

    //避免两种刷新冲突
    if(temp != words.size()) {
        myAdapter.notifyDataSetChanged();
    }
});

数据迁移

我们此时有一个需求，在原有的word表中增加一个字段，应该怎么做？

@PrimaryKey(autoGenerate = true)
private int id;

@ColumnInfo(name = "english_word")
private String word;

@ColumnInfo(name = "chinese_meaning")
private String chineseMeaning;

@ColumnInfo(name = "bar_data")
private boolean bar;

破坏式迁移

修改数据库的version和增加.fallbackToDestructiveMigration()，这种方式就是将现有结构清空，然后创建新的数据库，是一种破坏式的创建。不推荐

@Database(entities = {Word.class}, version = 2, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    private static WordDatabase INSTANCE;


    /**
    * @Description 单例获取
    * @date 2020/11/17 8:14
    * @param context
    * @return
    */
    public static synchronized WordDatabase getDatabase(Context context){
        if(INSTANCE == null){
            INSTANCE = Room.databaseBuilder(context, WordDatabase.class, "word_database")
                            //.allowMainThreadQueries()
                            .fallbackToDestructiveMigration()
                            .build();
        }
        return INSTANCE;
    }

    public abstract  WordDao getWordDao();
}

SQL语句方式(※)

其实就是运行一个sql语句，对表结构进行修改

@Database(entities = {Word.class}, version = 2, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    private static WordDatabase INSTANCE;


    /**
    * @Description 单例获取
    * @date 2020/11/17 8:14
    * @param context
    * @return
    */
    public static synchronized WordDatabase getDatabase(Context context){
        if(INSTANCE == null){
            INSTANCE = Room.databaseBuilder(context, WordDatabase.class, "word_database")
                            //.allowMainThreadQueries()
                            .addMigrations(MIGRATION_1_2)
                            .build();
        }
        return INSTANCE;
    }

    public abstract  WordDao getWordDao();

    static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("alter table word add  column bar_data INTEGER not null default 1");
        }
    };
}