显然，在oncreate方法中定义adapter后，public void selectquery(String query2){ List<NewContent> list2=Databasecontent.getInstance(this).sequery(query2.toLowerCase()); adapter.changeCursor(cursor); lvselect.setAdapter(adapter); }中仍然无法使用adapter

是的，你需要将 Adapterselect 对象声明为 Activity 的成员变量，以便在 selectquery() 方法中使用。你可以将 adapter 声明为以下形式：

private Adapterselect adapter;

然后，在 onCreate() 方法中初始化 adapter：

adapter = new Adapterselect(this, cursor, 0);
lvselect.setAdapter(adapter);

这样，在 selectquery() 方法中就可以直接使用 adapter 了：

public void selectquery(String query2) {
    List<NewContent> list2 = Databasecontent.getInstance(this).sequery(query2.toLowerCase());
    adapter.changeCursor(cursor);
    lvselect.setAdapter(adapter);
}

相关问题

怎么使用Camera2 拍照，并且将照片存储到Room数据库中，获取照片路径，在Recyclerview中显示，需要完整代码展示

好的，以下是完整代码展示，首先需要在build.gradle中添加Camera2和Room的依赖：

dependencies {
    // Camera2
    implementation 'com.android.support:support-v4:30.0.0'
    implementation 'com.android.support:appcompat-v7:30.0.0'
    implementation 'com.android.support:recyclerview-v7:30.0.0'
    implementation 'com.android.support:design:30.0.0'

    // Room
    implementation "androidx.room:room-runtime:2.3.0"
    annotationProcessor "androidx.room:room-compiler:2.3.0"
}

接下来是布局文件activity_main.xml：

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

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="8dp"
        tools:listitem="@layout/item_photo"/>

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:src="@drawable/ic_camera"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

布局文件item_photo.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:padding="8dp">

        <ImageView
            android:id="@+id/image_view"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:scaleType="centerCrop"/>

        <TextView
            android:id="@+id/text_view_path"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textStyle="italic"
            android:textColor="@color/colorAccent"/>

    </LinearLayout>

</androidx.cardview.widget.CardView>

接下来是MainActivity的代码：

public class MainActivity extends AppCompatActivity {

    private static final int REQUEST_CAMERA_PERMISSION = 1;
    private static final int REQUEST_IMAGE_CAPTURE = 2;

    private RecyclerView recyclerView;
    private FloatingActionButton fab;

    private PhotoAdapter adapter;

    private AppDatabase appDatabase;

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

        recyclerView = findViewById(R.id.recycler_view);
        fab = findViewById(R.id.fab);

        // 初始化RecyclerView
        adapter = new PhotoAdapter();
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(adapter);

        // 初始化数据库
        appDatabase = Room.databaseBuilder(getApplicationContext(), AppDatabase.class, "photo-db").build();

        // 点击拍照按钮
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ContextCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA}, REQUEST_CAMERA_PERMISSION);
                } else {
                    takePicture();
                }
            }
        });

        // 加载照片列表
        loadPhotos();
    }

    // 拍照
    private void takePicture() {
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        if (intent.resolveActivity(getPackageManager()) != null) {
            startActivityForResult(intent, REQUEST_IMAGE_CAPTURE);
        }
    }

    // 保存照片到数据库
    private void savePhoto(final String path) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                Photo photo = new Photo();
                photo.setPath(path);
                appDatabase.photoDao().insert(photo);
            }
        }).start();
    }

    // 加载照片列表
    private void loadPhotos() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                final List<Photo> photos = appDatabase.photoDao().getAll();
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        adapter.setPhotos(photos);
                    }
                });
            }
        }).start();
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            Bundle extras = data.getExtras();
            Bitmap imageBitmap = (Bitmap) extras.get("data");

            // 将照片保存到SD卡
            String path = saveImageToExternalStorage(imageBitmap);

            // 保存照片到数据库
            savePhoto(path);

            // 加载照片列表
            loadPhotos();
        }
    }

    // 将Bitmap保存到SD卡中
    private String saveImageToExternalStorage(Bitmap imageBitmap) {
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        String imageName = "JPEG_" + timeStamp + ".jpg";

        String path = Environment.getExternalStorageDirectory() + "/" + imageName;

        try {
            FileOutputStream fos = new FileOutputStream(path);
            imageBitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return path;
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        if (requestCode == REQUEST_CAMERA_PERMISSION && grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            takePicture();
        }
    }
}

接下来是Photo实体类：

@Entity
public class Photo {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String path;

    public int getId() {
        return id;
    }

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

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }
}

接下来是PhotoDao：

@Dao
public interface PhotoDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insert(Photo photo);

    @Query("SELECT * FROM photo")
    List<Photo> getAll();
}

接下来是AppDatabase：

@Database(entities = {Photo.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {

    public abstract PhotoDao photoDao();
}

最后是PhotoAdapter：

public class PhotoAdapter extends RecyclerView.Adapter<PhotoAdapter.PhotoViewHolder> {

    private List<Photo> photos;

    public void setPhotos(List<Photo> photos) {
        this.photos = photos;
        notifyDataSetChanged();
    }

    @NonNull
    @Override
    public PhotoViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_photo, parent, false);
        return new PhotoViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull PhotoViewHolder holder, int position) {
        Photo photo = photos.get(position);
        holder.imageView.setImageBitmap(BitmapFactory.decodeFile(photo.getPath()));
        holder.textViewPath.setText(photo.getPath());
    }

    @Override
    public int getItemCount() {
        return photos != null ? photos.size() : 0;
    }

    public static class PhotoViewHolder extends RecyclerView.ViewHolder {

        public ImageView imageView;
        public TextView textViewPath;

        public PhotoViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.image_view);
            textViewPath = itemView.findViewById(R.id.text_view_path);
        }
    }
}

以上就是完整的代码展示，希望能对你有所帮助。

用android studio,点击按钮可以在Dairy数据库中查看所有记录并显示在listview中，写出SQLite数据库创建和功能实现的完整过程

好的，下面是SQLite数据库创建和功能实现的完整过程：

1. 在 Android Studio 中创建一个新项目，并在项目的 `app/build.gradle` 文件中添加以下依赖项：

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.recyclerview:recyclerview:1.2.0'
    implementation 'androidx.cardview:cardview:1.0.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
    implementation 'androidx.room:room-runtime:2.3.0'
    annotationProcessor 'androidx.room:room-compiler:2.3.0'
}

2. 创建一个名为 `Diary` 的类，并使用 `@Entity` 注释将其标记为 Room 数据库表。

@Entity(tableName = "diary_table")
public class Diary {
    @PrimaryKey(autoGenerate = true)
    private int id;
    private String title;
    private String content;
    private String date;

    public Diary(String title, String content, String date) {
        this.title = title;
        this.content = content;
        this.date = date;
    }

    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;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }
}

3. 创建一个名为 `DiaryDao` 的接口，并使用 `@Dao` 注释将其标记为 Room 数据库访问对象。

@Dao
public interface DiaryDao {
    @Insert
    void insert(Diary diary);

    @Update
    void update(Diary diary);

    @Delete
    void delete(Diary diary);

    @Query("DELETE FROM diary_table")
    void deleteAllDiaries();

    @Query("SELECT * FROM diary_table ORDER BY id DESC")
    LiveData<List<Diary>> getAllDiaries();
}

4. 创建一个名为 `DiaryDatabase` 的类，并扩展 `RoomDatabase` 类。在 `DiaryDatabase` 类中，创建一个名为 `diaryDao` 的抽象方法，该方法返回 `DiaryDao` 接口的实现。

@Database(entities = {Diary.class}, version = 1)
public abstract class DiaryDatabase extends RoomDatabase {
    private static DiaryDatabase instance;

    public abstract DiaryDao diaryDao();

    public static synchronized DiaryDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    DiaryDatabase.class, "diary_database")
                    .fallbackToDestructiveMigration()
                    .build();
        }
        return instance;
    }
}

5. 在 MainActivity 类中，实例化 `DiaryViewModel` 类，并观察 `getAllDiaries()` 方法返回的 `LiveData` 对象，以便在数据库中添加，更新和删除数据时及时更新 UI。

public class MainActivity extends AppCompatActivity {
    private DiaryViewModel viewModel;
    private RecyclerView recyclerView;

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

        recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        final DiaryAdapter adapter = new DiaryAdapter();
        recyclerView.setAdapter(adapter);

        viewModel = new ViewModelProvider(this).get(DiaryViewModel.class);
        viewModel.getAllDiaries().observe(this, new Observer<List<Diary>>() {
            @Override
            public void onChanged(List<Diary> diaries) {
                adapter.submitList(diaries);
            }
        });
    }
}

6. 在 `MainActivity` 中实现添加、更新和删除数据的功能，以及在 `DiaryAdapter` 中实现 `ViewHolder` 和 `RecyclerView.Adapter` 的相关方法。

public class MainActivity extends AppCompatActivity {
    private DiaryViewModel viewModel;
    private RecyclerView recyclerView;

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

        recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        final DiaryAdapter adapter = new DiaryAdapter();
        recyclerView.setAdapter(adapter);

        viewModel = new ViewModelProvider(this).get(DiaryViewModel.class);
        viewModel.getAllDiaries().observe(this, new Observer<List<Diary>>() {
            @Override
            public void onChanged(List<Diary> diaries) {
                adapter.submitList(diaries);
            }
        });

        FloatingActionButton buttonAddDiary = findViewById(R.id.button_add_diary);
        buttonAddDiary.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, AddEditDiaryActivity.class);
                startActivityForResult(intent, ADD_DIARY_REQUEST);
            }
        });

        adapter.setOnItemClickListener(new DiaryAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(Diary diary) {
                Intent intent = new Intent(MainActivity.this, AddEditDiaryActivity.class);
                intent.putExtra(AddEditDiaryActivity.EXTRA_ID, diary.getId());
                intent.putExtra(AddEditDiaryActivity.EXTRA_TITLE, diary.getTitle());
                intent.putExtra(AddEditDiaryActivity.EXTRA_CONTENT, diary.getContent());
                intent.putExtra(AddEditDiaryActivity.EXTRA_DATE, diary.getDate());
                startActivityForResult(intent, EDIT_DIARY_REQUEST);
            }
        });
    }

    public static final int ADD_DIARY_REQUEST = 1;
    public static final int EDIT_DIARY_REQUEST = 2;

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == ADD_DIARY_REQUEST && resultCode == RESULT_OK) {
            String title = data.getStringExtra(AddEditDiaryActivity.EXTRA_TITLE);
            String content = data.getStringExtra(AddEditDiaryActivity.EXTRA_CONTENT);
            String date = data.getStringExtra(AddEditDiaryActivity.EXTRA_DATE);

            Diary diary = new Diary(title, content, date);
            viewModel.insert(diary);

            Toast.makeText(this, "Note saved", Toast.LENGTH_SHORT).show();
        } else if (requestCode == EDIT_DIARY_REQUEST && resultCode == RESULT_OK) {
            int id = data.getIntExtra(AddEditDiaryActivity.EXTRA_ID, -1);

            if (id == -1) {
                Toast.makeText(this, "Note can't be updated", Toast.LENGTH_SHORT).show();
                return;
            }

            String title = data.getStringExtra(AddEditDiaryActivity.EXTRA_TITLE);
            String content = data.getStringExtra(AddEditDiaryActivity.EXTRA_CONTENT);
            String date = data.getStringExtra(AddEditDiaryActivity.EXTRA_DATE);

            Diary diary = new Diary(title, content, date);
            diary.setId(id);
            viewModel.update(diary);

            Toast.makeText(this, "Note updated", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Note not saved", Toast.LENGTH_SHORT).show();
        }
    }
}

public class DiaryAdapter extends ListAdapter<Diary, DiaryAdapter.DiaryHolder> {
    private OnItemClickListener listener;

    public DiaryAdapter() {
        super(DIFF_CALLBACK);
    }

    private static final DiffUtil.ItemCallback<Diary> DIFF_CALLBACK = new DiffUtil.ItemCallback<Diary>() {
        @Override
        public boolean areItemsTheSame(@NonNull Diary oldItem, @NonNull Diary newItem) {
            return oldItem.getId() == newItem.getId();
        }

        @Override
        public boolean areContentsTheSame(@NonNull Diary oldItem, @NonNull Diary newItem) {
            return oldItem.getTitle().equals(newItem.getTitle()) &&
                    oldItem.getContent().equals(newItem.getContent()) &&
                    oldItem.getDate().equals(newItem.getDate());
        }
    };

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

    @Override
    public void onBindViewHolder(@NonNull DiaryHolder holder, int position) {
        Diary currentDiary = getItem(position);
        holder.textViewTitle.setText(currentDiary.getTitle());
        holder.textViewContent.setText(currentDiary.getContent());
        holder.textViewDate.setText(currentDiary.getDate());
    }

    public Diary getDiaryAt(int position) {
        return getItem(position);
    }

    class DiaryHolder extends RecyclerView.ViewHolder {
        private TextView textViewTitle;
        private TextView textViewContent;
        private TextView textViewDate;

        public DiaryHolder(View itemView) {
            super(itemView);
            textViewTitle = itemView.findViewById(R.id.text_view_title);
            textViewContent = itemView.findViewById(R.id.text_view_content);
            textViewDate = itemView.findViewById(R.id.text_view_date);

            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int position = getAdapterPosition();
                    if (listener != null && position != RecyclerView.NO_POSITION) {
                        listener.onItemClick(getItem(position));
                    }
                }
            });
        }
    }

    public interface OnItemClickListener {
        void onItemClick(Diary diary);
    }

    public void setOnItemClickListener(OnItemClickListener listener) {
        this.listener = listener;
    }
}

7. 创建一个名为 `AddEditDiaryActivity` 的活动，并在其中实现添加和更新数据的功能。同时，将数据传递回 `MainActivity`。

public class AddEditDiaryActivity extends AppCompatActivity {
    public static final String EXTRA_ID = "com.example.diary.EXTRA_ID";
    public static final String EXTRA_TITLE = "com.example.diary.EXTRA_TITLE";
    public static final String EXTRA_CONTENT = "com.example.diary.EXTRA_CONTENT";
    public static final String EXTRA_DATE = "com.example.diary.EXTRA_DATE";

    private EditText editTextTitle;
    private EditText editTextContent;
    private TextView textViewDate;

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

        editTextTitle = findViewById(R.id.edit_text_title);
        editTextContent = findViewById(R.id.edit_text_content);
        textViewDate = findViewById(R.id.text_view_date);

        getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_close);

        Intent intent = getIntent();
        if (intent.hasExtra(EXTRA_ID)) {
            setTitle("Edit Note");
            editTextTitle.setText(intent.getStringExtra(EXTRA_TITLE));
            editTextContent.setText(intent.getStringExtra(EXTRA_CONTENT));
            textViewDate.setText(intent.getStringExtra(EXTRA_DATE));
        } else {
            setTitle("Add Note");
            textViewDate.setText(getCurrentDate());
        }
    }

    private String getCurrentDate() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy.MM.dd HH:mm");
        return sdf.format(new Date());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.add_diary_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.save_diary:
                saveDiary();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    private void saveDiary() {
        String title = editTextTitle.getText().toString();
        String content = editTextContent.getText().toString();
        String date = textViewDate.getText().toString();

        if (title.trim().isEmpty() || content.trim().isEmpty()) {
            Toast.makeText(this, "Please insert a title and content", Toast.LENGTH_SHORT).show();
            return;
        }

        Intent data = new Intent();
        data.putExtra(EXTRA_TITLE, title);
        data.putExtra(EXTRA_CONTENT, content);
        data.putExtra(EXTRA_DATE, date);

        int id = getIntent().getIntExtra(EXTRA_ID, -1);
        if (id != -1) {
            data.putExtra(EXTRA_ID, id);
        }

        setResult(RESULT_OK, data);
        finish();
    }
}

这就是使用 SQLite 数据库在 Android Studio 中创建和实现功能的完整过程。