Android sqlite 存取图片完整示例

以下是一个完整的示例，演示如何使用SQLite存储和读取图片：

1. 创建数据库表

在创建SQLite数据库表时，需要添加一个BLOB类型的列，用于存储图片的二进制数据。示例代码如下：

public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "my_database";
    private static final int DB_VERSION = 1;
    private static final String TABLE_NAME = "image_table";
    private static final String ID_COLUMN = "id";
    private static final String NAME_COLUMN = "name";
    private static final String IMAGE_COLUMN = "image";

    public MyDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "CREATE TABLE " + TABLE_NAME + " (" +
                ID_COLUMN + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                NAME_COLUMN + " TEXT, " +
                IMAGE_COLUMN + " BLOB)";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // do nothing
    }
}

2. 存储图片

在存储图片时，需要将图片转换成二进制数据，并将其保存到数据库中。示例代码如下：

public void saveImageToDB(String name, byte[] image) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues cv = new ContentValues();
    cv.put(NAME_COLUMN, name);
    cv.put(IMAGE_COLUMN, image);
    db.insert(TABLE_NAME, null, cv);
    db.close();
}

其中，`name`是图片的名称，`image`是图片的二进制数据。

3. 读取图片

在读取图片时，需要从数据库中查询指定名称的图片，并将其转换成Bitmap对象。示例代码如下：

public Bitmap getImageFromDB(String name) {
    SQLiteDatabase db = this.getReadableDatabase();
    String[] columns = {IMAGE_COLUMN};
    String selection = NAME_COLUMN + "=?";
    String[] selectionArgs = {name};
    Cursor cursor = db.query(TABLE_NAME, columns, selection, selectionArgs, null, null, null);
    if (cursor.moveToFirst()) {
        byte[] image = cursor.getBlob(cursor.getColumnIndex(IMAGE_COLUMN));
        cursor.close();
        db.close();
        return BitmapFactory.decodeByteArray(image, 0, image.length);
    }
    cursor.close();
    db.close();
    return null;
}

其中，`name`是要读取的图片的名称，返回值是一个Bitmap对象。

4. 完整示例

以下是一个完整的示例，演示如何使用SQLite存储和读取图片：

public class MainActivity extends AppCompatActivity {
    private static final int REQUEST_CODE = 1;
    private ImageView imageView;
    private MyDatabaseHelper dbHelper;

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

        dbHelper = new MyDatabaseHelper(this);
        imageView = findViewById(R.id.image_view);

        Button selectButton = findViewById(R.id.select_button);
        selectButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Intent.ACTION_PICK);
                intent.setType("image/*");
                startActivityForResult(intent, REQUEST_CODE);
            }
        });

        Button saveButton = findViewById(R.id.save_button);
        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Bitmap bitmap = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
                byte[] image = getBitmapAsByteArray(bitmap);
                dbHelper.saveImageToDB("my_image", image);
                Toast.makeText(MainActivity.this, "Image saved to database", Toast.LENGTH_SHORT).show();
            }
        });

        Button loadButton = findViewById(R.id.load_button);
        loadButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Bitmap bitmap = dbHelper.getImageFromDB("my_image");
                if (bitmap != null) {
                    imageView.setImageBitmap(bitmap);
                } else {
                    Toast.makeText(MainActivity.this, "Image not found in database", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
            Uri uri = data.getData();
            imageView.setImageURI(uri);
        }
    }

    private byte[] getBitmapAsByteArray(Bitmap bitmap) {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);
        return outputStream.toByteArray();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        dbHelper.close();
    }
}

以上示例代码仅供参考，实际使用时需要进行适当修改。另外，存储图片到SQLite中并不是一个好的做法，建议存储图片到文件系统中，然后在数据库中存储图片的路径。