recyclerview+fab

recyclerview+fab 是指在 Android 应用中使用 RecyclerView 和 FloatingActionButton（简称 FAB）的组合。RecyclerView 是一个强大的列表控件，可以高效地显示大量数据，而 FAB 则是一个浮动操作按钮，通常用于触发应用中的主要操作。

相关问题

<?xml version="1.0" encoding="utf-8"?> <ScrollView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical"> <RecyclerView android:id="@+id/recycler_view" android:layout_width="match_parent" android:layout_height="wrap_content" /> <android.support.design.widget.FloatingActionButton android:id="@+id/fab_add_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="bottom|end" android:layout_margin="16dp" android:src="@drawable/add" android:contentDescription="@string/add_button_description"/> </LinearLayout> </ScrollView> 报错Cannot resolve class RecyclerView

这个错误通常是因为没有在项目的 build.gradle 文件中添加 RecyclerView 的依赖。你可以尝试将以下代码添加到你的 build.gradle 文件中：

dependencies {
    implementation 'com.android.support:recyclerview-v7:28.0.0'
}

如果你已经添加了这个依赖但是仍然遇到问题，可以尝试在 Android Studio 中点击 "File" -> "Invalidate Caches / Restart" 重启 Android Studio。如果问题仍然存在，你可以尝试清除项目的 Gradle 缓存，方法是在命令行中运行 `./gradlew clean`。

Android sqlite recyclerview 完整示例

以下是一个简单的 Android SQLite RecyclerView 完整示例：

1. 创建一个名为 "Note" 的 Java 类表示笔记：

public class Note {
    private int id;
    private String title;
    private String content;

    public Note() {}

    public Note(int id, String title, String content) {
        this.id = id;
        this.title = title;
        this.content = content;
    }

    public int getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

2. 创建一个名为 "NoteDatabaseHelper" 的类用于创建和管理 SQLite 数据库：

public class NoteDatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "notes_db";
    private static final int DATABASE_VERSION = 1;

    private static final String TABLE_NAME = "notes";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_TITLE = "title";
    private static final String COLUMN_CONTENT = "content";

    public NoteDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY,"
                + COLUMN_TITLE + " TEXT,"
                + COLUMN_CONTENT + " TEXT" + ")";
        db.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }

    public void addNote(Note note) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(COLUMN_TITLE, note.getTitle());
        values.put(COLUMN_CONTENT, note.getContent());

        db.insert(TABLE_NAME, null, values);
        db.close();
    }

    public List<Note> getAllNotes() {
        List<Note> notesList = new ArrayList<>();

        String selectQuery = "SELECT  * FROM " + TABLE_NAME;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        if (cursor.moveToFirst()) {
            do {
                Note note = new Note();
                note.setId(cursor.getInt(0));
                note.setTitle(cursor.getString(1));
                note.setContent(cursor.getString(2));
                notesList.add(note);
            } while (cursor.moveToNext());
        }

        cursor.close();
        db.close();

        return notesList;
    }

    public void updateNote(Note note) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(COLUMN_TITLE, note.getTitle());
        values.put(COLUMN_CONTENT, note.getContent());

        db.update(TABLE_NAME, values, COLUMN_ID + " = ?",
                new String[] { String.valueOf(note.getId()) });
        db.close();
    }

    public void deleteNote(Note note) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_NAME, COLUMN_ID + " = ?",
                new String[] { String.valueOf(note.getId()) });
        db.close();
    }
}

3. 创建一个名为 "NoteAdapter" 的类来显示笔记列表：

public class NoteAdapter extends RecyclerView.Adapter<NoteAdapter.MyViewHolder> {
    private List<Note> notesList;

    public class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView title, content;

        public MyViewHolder(View view) {
            super(view);
            title = view.findViewById(R.id.title);
            content = view.findViewById(R.id.content);
        }
    }

    public NoteAdapter(List<Note> notesList) {
        this.notesList = notesList;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.note_list_row, parent, false);

        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        Note note = notesList.get(position);
        holder.title.setText(note.getTitle());
        holder.content.setText(note.getContent());
    }

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

4. 创建一个名为 "MainActivity" 的 Activity，显示 RecyclerView：

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private NoteAdapter noteAdapter;
    private List<Note> notesList = new ArrayList<>();
    private NoteDatabaseHelper databaseHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recycler_view);
        databaseHelper = new NoteDatabaseHelper(this);

        notesList.addAll(databaseHelper.getAllNotes());

        noteAdapter = new NoteAdapter(notesList);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(noteAdapter);
    }

    @Override
    protected void onResume() {
        super.onResume();
        notesList.clear();
        notesList.addAll(databaseHelper.getAllNotes());
        noteAdapter.notifyDataSetChanged();
    }

    public void addNewNote() {
        Note note = new Note();
        note.setTitle("Title");
        note.setContent("Content");

        databaseHelper.addNote(note);
        notesList.add(note);
        noteAdapter.notifyItemInserted(notesList.size() - 1);
    }
}

5. 创建一个名为 "activity_main.xml" 的布局文件来显示 RecyclerView：

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="16dp"
        android:clipToPadding="false" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        android:layout_marginBottom="16dp"
        android:layout_marginEnd="16dp"
        android:clickable="true"
        android:src="@drawable/ic_add_white_24dp" />

</RelativeLayout>

6. 创建一个名为 "note_list_row.xml" 的布局文件来显示每个笔记：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="8dp">

    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/title"
        android:textSize="14sp"
        android:textColor="@android:color/darker_gray" />

</RelativeLayout>

7. 在 MainActivity 中添加一个 FloatingActionButton 来添加新笔记：

FloatingActionButton fab = findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        addNewNote();
    }
});

这是一个简单的 Android SQLite RecyclerView 完整示例，它可以让你了解如何在 Android 应用中使用 SQLite 和 RecyclerView。