我是android新手。我目前正在开发一个android应用。 SQLite数据库中有图像，SQLite数据库中也将添加图像。 SQLite数据库中的图像当前需要一些时间来加载。我想将列表视图中的图像存储到内存缓存中以增加执行时间。有人能帮忙吗？下面是我目前的代码，它可以正常运行。
FoodList.java：
public class FoodList extends AppCompatActivity{
ListView listView;
ArrayList <Food> list;
FoodListAdapter adapter = null;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.food_list);
listView = (ListView) findViewById(R.id.listView);
list = new ArrayList<>();
adapter = new FoodListAdapter(this,R.layout.food_items,list);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
String item = list.get(i).getPrice();
Toast.makeText(getApplicationContext(),"Hi"+item,Toast.LENGTH_SHORT).show();
//getIntent().putExtra("ListItem",list.get(i).getPrice());
Intent intent = new Intent(FoodList.this,Activity2.class);
startActivity(intent);
}
});
//get all data
Cursor cursor = MainActivity.sqLiteHelper.getData("SELECT * FROM FOOD");
list.clear();
while (cursor.moveToNext())
{
int id = cursor.getInt(0);
String name = cursor.getString(1);
String price = cursor.getString(2);
byte [] image = cursor.getBlob(3);
list.add(new Food(id,name,price,image));
}
Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.mipmap.newsgd);
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG,100,stream);
byte[] singaporeCoin = stream.toByteArray();
Bitmap bitmap1 = BitmapFactory.decodeResource(getResources(),R.mipmap.q2);
ByteArrayOutputStream stream1 = new ByteArrayOutputStream();
bitmap1.compress(Bitmap.CompressFormat.PNG,100,stream1);
byte[] usCoin = stream1.toByteArray();
Bitmap bitmap2 = BitmapFactory.decodeResource(getResources(),R.mipmap.y1);
ByteArrayOutputStream stream2 = new ByteArrayOutputStream();
bitmap2.compress(Bitmap.CompressFormat.PNG,100,stream2);
byte[] chinaCoin = stream2.toByteArray();
list.add(new Food(-1,"Singapore","4.77",singaporeCoin));
list.add(new Food(-2,"United States","4.62",usCoin));
list.add(new Food(-3,"China","4.90",chinaCoin));
adapter.notifyDataSetChanged();
}
}
MainActivity.java：
public class MainActivity extends AppCompatActivity {
EditText edtName, edtPrice;
Button btnChoose, btnAdd, btnList;
ImageView imageView;
final int REQUEST_CODE_GALLERY =999;
public static SQLiteHelper sqLiteHelper;
@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(id INTEGER PRIMARY KEY AUTOINCREMENT,name VARCHAR, price VARCHAR,image BLOG)");
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(),"Added successfully!",Toast.LENGTH_SHORT).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(),"You don't have the permission",Toast.LENGTH_SHORT).show();
}
return;
}
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
}
@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 = (EditText) findViewById(R.id.et_name);
edtPrice = (EditText) findViewById(R.id.et_Price);
btnChoose = (Button) findViewById(R.id.bt_chose);
btnAdd = (Button) findViewById(R.id.bt_add);
btnList = (Button) findViewById(R.id.bt_listt);
imageView = (ImageView) findViewById(R.id.imageView);
}
}
FoodListAdapter.java：
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;
Button btnDelete;
}
@Override
public View getView(final 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;
}
}
SQLiteHelper.java：
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 (NULL,?,?,?)";
SQLiteStatement statement = database.compileStatement(sql);
statement.bindString(1,name);
statement.bindString(2,price);
statement.bindBlob(3,image);
statement.executeInsert();
statement.clearBindings();
}
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) {
}
}