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Room (三) RecyclerView 呈现列表数据

news 来源：原创 2024/4/27 19:06:29

1. 用到的组件 Room，ViewModel，LiveData，Repository，AsyncTack

2. Module 中 build.gradle 文件中添加

dependencies {
    def room_version = "2.4.3"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
}

3. 数据操作

3.1 Word 实体类, Word.java

@Entity
public class Word {
    @PrimaryKey(autoGenerate = true)
    private int id; //主键
    @ColumnInfo(name = "english_word")
    private String word;
    @ColumnInfo(name = "chinese_meaning")
    private String chineseMeaning;

    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 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;
    }
}

3.2 实现 Database 接口, WordDao.java

@Dao //Database access object
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")
    LiveData<List<Word>> getAllWordsLive();
    //List<Word> getAllWords();
}

3.3 Database 管理操作数据库, WordDatabase.java

//singleton 只允许生成一个实例
@Database(entities = {Word.class}, version = 1, exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {
    private static WordDatabase INSTANCE;

    //synchronized: 解决多个线程下调用，创建多个实例问题
    static synchronized WordDatabase getDatabase(Context context) {
        if (INSTANCE == null) {
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
                    .build();
        }
        return INSTANCE;
    }

    public abstract WordDao getWordDao();
}

3.4 Repository 操作数据库, WordRepository.java

//Repository 仓库 获取数据的意思
class WordRepository {
    private WordDao wordDao;
    private LiveData<List<Word>> allWordsLive;

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

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

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

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

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

    void deleteAllWords() {
        new DeleteAllAsyncTask(wordDao).execute();
    }

    static class InsertAsyncTask extends AsyncTask<Word, Void, Void> {
        private WordDao wordDao;

        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;

        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;

        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;

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

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

4. 实现 ViewModel, WordViewModel.java

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();
    }

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

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

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

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

5. RecyclerView 的实现

5.1 资源文件进入页面提示标志 ic_baseline_chevron_right_24.xml

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="24dp"
    android:height="24dp"
    android:tint="@android:color/secondary_text_dark_nodisable"
    android:viewportWidth="24"
    android:viewportHeight="24">
    <path
        android:fillColor="@android:color/white"
        android:pathData="M10,6L8.59,7.41 13.17,12l-4.58,4.59L10,18l6,-6z" />
</vector>

5.2 列表子布局常规 item, cell_normal.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/selectableItemBackground"
    android:clickable="true">

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.1" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.85" />

    <TextView
        android:id="@+id/tv_number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        android:textSize="16sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline3"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="1" />

    <TextView
        android:id="@+id/tv_english"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="TextView"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/tv_chinese"
        app:layout_constraintStart_toStartOf="@+id/tv_chinese"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_chinese"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:text="TextView"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline4"
        app:layout_constraintHorizontal_bias="0.02"
        app:layout_constraintStart_toStartOf="@+id/guideline3"
        app:layout_constraintTop_toBottomOf="@+id/tv_english" />

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline4"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_baseline_chevron_right_24" />
</androidx.constraintlayout.widget.ConstraintLayout>

5.3 列表子布局 cardView item, cell_card.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:clickable="true">

    <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:foreground="?attr/selectableItemBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <TextView
                android:id="@+id/tv_number"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView"
                android:textSize="16sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toStartOf="@+id/guideline5"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                tools:text="1" />

            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline5"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_percent="0.1" />

            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline6"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_percent="0.85" />

            <TextView
                android:id="@+id/tv_english"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="8dp"
                android:text="TextView"
                android:textSize="24sp"
                app:layout_constraintBottom_toTopOf="@+id/tv_chinese"
                app:layout_constraintEnd_toStartOf="@+id/guideline6"
                app:layout_constraintHorizontal_bias="0.02"
                app:layout_constraintStart_toStartOf="@+id/guideline5"
                app:layout_constraintTop_toTopOf="parent" />

            <TextView
                android:id="@+id/tv_chinese"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="8dp"
                android:text="TextView"
                android:textSize="18sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintStart_toStartOf="@+id/tv_english"
                app:layout_constraintTop_toBottomOf="@+id/tv_english" />

            <ImageView
                android:id="@+id/imageView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="@+id/guideline6"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/ic_baseline_chevron_right_24" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.cardview.widget.CardView>
</androidx.constraintlayout.widget.ConstraintLayout>

5.4 RecyclerView 内容管理器 Adapter, MyAdapter.java

//内容管理器
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
    private List<Word> allWords = new ArrayList<>();
    private boolean useCardView;

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

    public MyAdapter(boolean useCardView) {
        this.useCardView = useCardView;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View itemView;
        if (useCardView) {
            itemView = layoutInflater.inflate(R.layout.cell_card, parent, false);
        } else {
            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.tvNumber.setText(String.valueOf(position + 1));
        holder.tvEnglish.setText(word.getWord());
        holder.tvChinese.setText(word.getChineseMeaning());
        holder.itemView.setOnClickListener(view -> {
            Uri uri = Uri.parse("https://m.youdao.com/m/result?lang=en&word=" + word.getWord());
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setData(uri);
            holder.itemView.getContext().startActivity(intent);
        });
    }
    
    @Override
    public int getItemCount() {
        return allWords.size();
    }

    static class MyViewHolder extends RecyclerView.ViewHolder {
        TextView tvNumber, tvEnglish, tvChinese;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            tvNumber = itemView.findViewById(R.id.tv_number);
            tvEnglish = itemView.findViewById(R.id.tv_english);
            tvChinese = itemView.findViewById(R.id.tv_chinese);
        }
    }
}

6. 测试调用

6.1 布局文件，activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.85" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/guideline2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/bt_clear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Clear"
        app:layout_constraintBottom_toBottomOf="@+id/switch1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/switch1"
        app:layout_constraintTop_toTopOf="@+id/switch1" />

    <Button
        android:id="@+id/bt_insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="insert"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/switch1"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/guideline2" />

    <Switch
        android:id="@+id/switch1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:minHeight="48dp"
        android:text="CardView"
        app:layout_constraintBottom_toBottomOf="@+id/bt_insert"
        app:layout_constraintEnd_toStartOf="@+id/bt_clear"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/bt_insert"
        app:layout_constraintTop_toTopOf="@+id/bt_insert" />

</androidx.constraintlayout.widget.ConstraintLayout>

6.2 测试文件，MainActivity. java

public class MainActivity extends AppCompatActivity {
    Button btInsert, btClear;
    Switch aSwitch;
    WordViewModel viewModel;
    RecyclerView recyclerView;
    MyAdapter myAdapter1, myAdapter2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myAdapter1 = new MyAdapter(false);
        myAdapter2 = new MyAdapter(true);

        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(myAdapter1);
        aSwitch = findViewById(R.id.switch1);
        aSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean isChanged) {
                if (isChanged) {
                    recyclerView.setAdapter(myAdapter2);
                } else {
                    recyclerView.setAdapter(myAdapter1);
                }
            }
        });

        viewModel = new ViewModelProvider(this).get(WordViewModel.class);
        viewModel.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                myAdapter1.setAllWords(words);
                myAdapter1.notifyDataSetChanged();
                myAdapter2.setAllWords(words);
                myAdapter2.notifyDataSetChanged();
            }
        });

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                switch (view.getId()) {
                    case R.id.bt_insert:
                        String[] english = {
                                "Hello",
                                "World",
                                "Android",
                                "Google",
                                "Studio",
                                "Project",
                                "Database",
                                "Recycler",
                                "View",
                                "String",
                                "Value",
                                "Integer"
                        };
                        String[] chinese = {
                                "你好",
                                "世界",
                                "安卓",
                                "谷歌",
                                "工作室",
                                "项目",
                                "数据库",
                                "回收站",
                                "视图",
                                "字符串",
                                "值",
                                "整数类型"
                        };
                        for (int i = 0; i < english.length; i++) {
                            viewModel.insertWords(new Word(english[i], chinese[i]));
                        }
                        break;
                    case R.id.bt_clear:
                        viewModel.deleteAllWords();
                        break;
                }
            }
        };
        btInsert = findViewById(R.id.bt_insert);
        btClear = findViewById(R.id.bt_clear);
        btInsert.setOnClickListener(listener);
        btClear.setOnClickListener(listener);
    }
}