要将Cursor转换为Room Entity,请使用CursorAdapter或SimpleCursorAdapter。一个可能的示例:
首先,在Room Entity中定义一个构造函数,以从Cursor中提取数据并创建对象。例如:
@Entity(tableName = "students") public class Student { @PrimaryKey(autoGenerate = true) private int id; private String name; private int age;
// Constructor for CursorAdapter/SimpleCursorAdapter public Student(Cursor cursor){ this.id = cursor.getInt(cursor.getColumnIndex("id")); this.name = cursor.getString(cursor.getColumnIndex("name")); this.age = cursor.getInt(cursor.getColumnIndex("age")); }
// Constructor for regular Room queries public Student(int id, String name, int age) { this.id = id; this.name = name; this.age = age; }
// Getters and setters... }
然后,在DAO中编写查询方法,并将其返回类型定义为Cursor:
@Dao public interface StudentDao { @Query("SELECT * FROM students") Cursor getAllStudentsCursor(); }
最后,在调用DAO方法时,使用CursorAdapter或SimpleCursorAdapter来将Cursor转换为实体对象列表:
Cursor cursor = studentDao.getAllStudentsCursor();
String[] fromColumns = { "name", "age" }; int[] toViews = { R.id.nameTextView, R.id.ageTextView };
SimpleCursorAdapter adapter = new SimpleCursorAdapter( this, R.layout.list_item, cursor, fromColumns, toViews, 0);
ListView listView = findViewById(R.id.listView); listView.setAdapter(adapter);
如果需要使用RecyclerView,则可以实现CursorAdapter的getItemCount()和onBindViewHolder()方法。具体而言,我们可以将CursorAdapter子类化为RecyclerView.Adapter
public class StudentCursorAdapter extends RecyclerView.Adapter
private Cursor cursor;
public StudentCursorAdapter(Cursor cursor) { this.cursor = cursor; }
// Create new views (invoked by the layout manager) @Override public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { // create a new view View v = LayoutInflater.from(parent.getContext()) .inflate(R.layout.list_item, parent, false); // set the view's size, margins, paddings and layout parameters ViewHolder vh = new ViewHolder(v); return vh; }
// Replace the contents of a view (invoked by the layout manager) @Override public void onBindViewHolder(ViewHolder holder, int position) { cursor.moveTo