Room (五) 数据库结构的改变与版本迁移

1. 数据库添加 chinese_invisible 字段，标识显示或者隐藏View

  1.1 修改 Word 类

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

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

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

    public boolean isChineseInvisible() {
        return chineseInvisible;
    }

    public void setChineseInvisible(boolean chineseInvisible) {
        this.chineseInvisible = chineseInvisible;
    }


//    public boolean isBar() {
//        return bar;
//    }
//
//    public void setBar(boolean bar) {
//        this.bar = bar;
//    }
//
//    public boolean isFoo() {
//        return foo;
//    }
//
//    public void setFoo(boolean foo) {
//        this.foo = foo;
//    }

    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;
    }
}

  1.2 修改 WordDatabase 类，修改数据库版本和策略

//singleton 只允许生成一个实例
@Database(entities = {Word.class}, version = 5, 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) {
            //fallbackToDestructiveMigration 把当前的数据清空，创建新的库
            //addMigrations 添加迁移的策略
            INSTANCE = Room.databaseBuilder(context.getApplicationContext(), WordDatabase.class, "word_database")
                    .addMigrations(migration_4_5)
                    .build();
        }
        return INSTANCE;
    }

    public abstract WordDao getWordDao();


    static final Migration migration_4_5 = new Migration(4, 5) {
        @Override
        public void migrate(@NonNull SupportSQLiteDatabase database) {
            database.execSQL("ALTER TABLE word ADD COLUMN chinese_invisible INTEGER NOT NULL DEFAULT 0");
        }
    };
}

2. 修改 RecyclerView 的 item View

  2.1 添加 cell_normal_2.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="60dp"
    android:foreground="?attr/selectableItemBackground">

    <View
        android:id="@+id/divider"
        android:layout_width="1dp"
        android:layout_height="0dp"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:background="?android:attr/listDivider"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="@+id/constraintLayout2"
        app:layout_constraintStart_toStartOf="@+id/guideline7"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/constraintLayout2"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/guideline7"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.15" />

        <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/guideline10"
            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_marginStart="16dp"
            android:text="TextView"
            android:textSize="24sp"
            app:layout_constraintBottom_toTopOf="@+id/tv_chinese"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="@+id/guideline10"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tv_chinese"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            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" />

    </androidx.constraintlayout.widget.ConstraintLayout>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/constraintLayout"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@+id/guideline7"
        app:layout_constraintTop_toTopOf="parent">

        <Switch
            android:id="@+id/switchChineseInvisible"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:paddingStart="30dp"
            android:paddingEnd="15dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            tools:ignore="UseSwitchCompatOrMaterialXml" />

    </androidx.constraintlayout.widget.ConstraintLayout>

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline7"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.8" />
</androidx.constraintlayout.widget.ConstraintLayout>

  2.2 添加 cell_card_2.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="70dp">

    <androidx.cardview.widget.CardView
        android:layout_width="0dp"
        android:layout_height="0dp"
        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">

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

            <View
                android:id="@+id/divider2"
                android:layout_width="1dp"
                android:layout_height="0dp"
                android:layout_marginTop="8dp"
                android:background="?android:attr/listDivider"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toStartOf="@+id/guideline9"
                app:layout_constraintStart_toEndOf="@+id/guideline9"
                app:layout_constraintTop_toTopOf="parent" />

            <androidx.constraintlayout.widget.ConstraintLayout
                android:id="@+id/constraintLayout"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toStartOf="@+id/guideline9"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent">

                <androidx.constraintlayout.widget.Guideline
                    android:id="@+id/guideline11"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="vertical"
                    app:layout_constraintGuide_percent="0.15" />

                <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/guideline11"
                    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_marginStart="16dp"
                    android:text="TextView"
                    android:textSize="24sp"
                    app:layout_constraintBottom_toTopOf="@+id/tv_chinese"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintHorizontal_bias="0.0"
                    app:layout_constraintStart_toStartOf="@+id/guideline11"
                    app:layout_constraintTop_toTopOf="parent" />

                <TextView
                    android:id="@+id/tv_chinese"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    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" />

            </androidx.constraintlayout.widget.ConstraintLayout>

            <androidx.constraintlayout.widget.ConstraintLayout
                android:id="@+id/constraintLayout2"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="@+id/guideline9"
                app:layout_constraintTop_toTopOf="parent">

                <Switch
                    android:id="@+id/switchChineseInvisible"
                    android:layout_width="wrap_content"
                    android:layout_height="0dp"
                    android:paddingStart="30dp"
                    android:paddingEnd="15dp"
                    app:layout_constraintBottom_toBottomOf="parent"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent" />
            </androidx.constraintlayout.widget.ConstraintLayout>

            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline9"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_percent="0.8" />

        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.cardview.widget.CardView>
</androidx.constraintlayout.widget.ConstraintLayout>

3. 修改适配器 Adapter

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

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

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

    @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_2, parent, false);
        } else {
            itemView = layoutInflater.inflate(R.layout.cell_normal_2, 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());
        //设置为空，防止再次调用 OnCheckedChangeListener 监听
        holder.aSwitchChineseInvisible.setOnCheckedChangeListener(null);
        if (word.isChineseInvisible()) {
            holder.tvChinese.setVisibility(View.GONE);
            holder.aSwitchChineseInvisible.setChecked(true);
        } else {
            holder.tvChinese.setVisibility(View.VISIBLE);
            holder.aSwitchChineseInvisible.setChecked(false);
        }
        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);
        });

        holder.aSwitchChineseInvisible.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
                if (isChecked) {
                    holder.tvChinese.setVisibility(View.GONE);
                    word.setChineseInvisible(true);
                    viewModel.updateWords(word);
                } else {
                    holder.tvChinese.setVisibility(View.VISIBLE);
                    word.setChineseInvisible(false);
                    viewModel.updateWords(word);
                }
            }
        });
    }

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

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

        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);
            aSwitchChineseInvisible = itemView.findViewById(R.id.switchChineseInvisible);
        }
    }
}

4. 测试调用 MainActivity

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);
        viewModel = new ViewModelProvider(this).get(WordViewModel.class);

        myAdapter1 = new MyAdapter(false, viewModel);
        myAdapter2 = new MyAdapter(true, viewModel);

        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.getAllWordsLive().observe(this, new Observer<List<Word>>() {
            @Override
            public void onChanged(List<Word> words) {
                int size = myAdapter1.getItemCount();
                myAdapter1.setAllWords(words);
                myAdapter2.setAllWords(words);
                if (size != words.size()) {
                    myAdapter1.notifyDataSetChanged();
                    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);
    }
}

5. 效果图