这篇文章是我之前关于将图像保存到SQLite的问题的延续。我得到无法在FoodList活动启动时将Blob转换为String错误。我正在使用SQLite Helper和适配器。我的主要活动代码如下：
public static SQLiteHelper sqLiteHelper;
final int REQUEST_CODE_GALLERY = 999;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
init();
sqLiteHelper = new SQLiteHelper(this, "FoodDB.sqlite", null, 1);
sqLiteHelper.queryData("CREATE TABLE IF NOT EXISTS FOOD (name TEXT, price TEXT, image BLOB)");
btnChoose.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ActivityCompat.requestPermissions(
MainActivity.this,
new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
REQUEST_CODE_GALLERY
);
}
});
btnAdd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
try {
sqLiteHelper.insertData(
edtName.getText().toString().trim(),
edtPrice.getText().toString().trim(),
imageViewToByte(imageView)
);
Toast.makeText(getApplicationContext(), "Entry Added", Toast.LENGTH_LONG).show();
edtName.setText("");
edtPrice.setText("");
imageView.setImageResource(R.mipmap.ic_launcher);
}
catch(Exception e)
{
e.printStackTrace();
}
}
});
btnList.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, FoodList.class);
startActivity(intent);
}
});
}
private byte[] imageViewToByte(ImageView image) {
Bitmap bitmap = ((BitmapDrawable)image.getDrawable()).getBitmap();
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteArray = stream.toByteArray();
return byteArray;
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
if(requestCode == REQUEST_CODE_GALLERY) {
if(grantResults.length >0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Intent intent = new Intent(Intent.ACTION_PICK);
intent.setType("image/*");
startActivityForResult(intent, REQUEST_CODE_GALLERY);
}
else {
Toast.makeText(getApplicationContext(), "Permission Denied", Toast.LENGTH_LONG).show();
}
//return;
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if(requestCode == REQUEST_CODE_GALLERY && resultCode == RESULT_OK && data != null) {
Uri uri = data.getData();
try {
InputStream inputStream = getContentResolver().openInputStream(uri);
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
imageView.setImageBitmap(bitmap);
}
catch (FileNotFoundException e){
e.printStackTrace();
}
}
super.onActivityResult(requestCode, resultCode, data);
}
private void init() {
edtName = findViewById(R.id.edtName);
edtPrice = findViewById(R.id.edtPrice);
btnChoose = findViewById(R.id.btnChoose);
btnAdd = findViewById(R.id.btnAdd);
btnList = findViewById(R.id.btnList);
imageView = findViewById(R.id.imageView);
}
}
然后我的SQLite Helper类如下：
public class SQLiteHelper extends SQLiteOpenHelper {
public SQLiteHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
public void queryData(String sql) {
SQLiteDatabase database = getWritableDatabase();
database.execSQL(sql);
}
public void insertData(String name, String price, byte[] image) {
SQLiteDatabase database = getWritableDatabase();
String sql = "INSERT INTO FOOD VALUES (?, ?, ?)";
SQLiteStatement statement = database.compileStatement(sql);
statement.clearBindings();
statement.bindString(1, name);
statement.bindString(2, price);
statement.bindBlob(3, image);
statement.executeInsert();
}
public Cursor getData(String sql) {
SQLiteDatabase database = getReadableDatabase();
return database.rawQuery(sql, null);
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
}
我的食物清单适配器代码是这样的：
public class FoodListAdapter extends BaseAdapter {
private Context context;
private int layout;
private ArrayList<Food> foodsList;
public FoodListAdapter(Context context, int layout, ArrayList<Food> foodsList) {
this.context = context;
this.layout = layout;
this.foodsList = foodsList;
}
@Override
public int getCount() {
return foodsList.size();
}
@Override
public Object getItem(int position) {
return foodsList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
private class ViewHolder {
ImageView imageView;
TextView txtName, txtPrice;
}
@Override
public View getView(int position, View view, ViewGroup viewGroup) {
View row = view;
ViewHolder holder = new ViewHolder();
if(row == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = inflater.inflate(layout, null);
holder.txtName = (TextView) row.findViewById(R.id.txtName);
holder.txtPrice = (TextView) row.findViewById(R.id.txtPrice);
holder.imageView = (ImageView) row.findViewById(R.id.imgFood);
row.setTag(holder);
}
else {
holder = (ViewHolder) row.getTag();
}
Food food = foodsList.get(position);
holder.txtName.setText(food.getName());
holder.txtPrice.setText(food.getPrice());
byte[] foodImage = food.getImage();
Bitmap bitmap = BitmapFactory.decodeByteArray(foodImage, 0, foodImage.length);
holder.imageView.setImageBitmap(bitmap);
return row;
}
}
我还有一个名为Food的类，代码也如下：
public class Food {
private String name;
private String price;
private byte[] image;
public Food(String name, String price, byte[] image) {
this.name = name;
this.price = price;
this.image = image;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
public byte[] getImage() {
return image;
}
public void setImage(byte[] image) {
this.image = image;
}
}
最后但并非最不重要的是，这里是在初始化FoodList时崩溃的活动的代码：
public class FoodList extends AppCompatActivity {
GridView gridView;
ArrayList<Food> list;
FoodListAdapter adapter;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.food_list_activity);
gridView = findViewById(R.id.gridView);
list = new ArrayList<>();
adapter = new FoodListAdapter(this, R.layout.food_items, list);
gridView.setAdapter(adapter);
Cursor cursor = MainActivity.sqLiteHelper.getData("SELECT * FROM FOOD");
list.clear();
while (cursor.moveToNext()) {
String name = cursor.getString(1);
String price = cursor.getString(2);
byte[] image = cursor.getBlob(3);
list.add(new Food(name, price, image));
}
adapter.notifyDataSetChanged();
}
}
我不知道造成这个错误的原因。希望有人可以对我的问题有所了解......
Cursor cursor = MainActivity.sqLiteHelper.getData("SELECT * FROM FOOD");
将返回一个有3列，名称，价格和图像的光标，因此您将拥有偏移0（名称），1（价格）和2（图像）的列。
因此，getString(2)正在尝试获取作为BLOB的image列，但是作为String，因此尝试将BLOB转换为String时出错。
如果它没有失败那么你会因getBlob(3)的索引错误而失败，因为没有偏移量为3的列。
最好不要正常使用偏移，而是使用getColumnIndex(column_name)方法，该方法根据给定的列名返回列偏移量（索引）。
因此，您可以使用以下方法来解决问题： -
String name = cursor.getString(getColumnIndex("name"));
String price = cursor.getString(getColumnIndex("price"));
byte[] image = cursor.getBlob(getColumnIndex("image"));