我做过研究，但找不到明确的解释，我知道之前有人问过，但我仍然没有解决方法。
我有一个由sqlite填充的gridView。问题是我的gridView的滚动有滞后。我的代码 -
适配器;
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{
CircularImageView 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 = (CircularImageView) 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;
}
}
活性;
public class FoodList extends AppCompatActivity {
GridView gridView;
ArrayList<Food> list;
AdapterView adapterView;
FoodListAdapter adapter = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.student_list_activity);
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 BLOB)");
gridView = (GridView) findViewById(R.id.gridView);
list = new ArrayList<>();
adapter = new FoodListAdapter(this, R.layout.food_items, list);
gridView.setAdapter(adapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String dataFromGrid;
dataFromGrid = ((TextView)(view.findViewById(R.id.txtName))).getText().toString();
Intent i = new Intent(getApplicationContext(), FoodInfo.class);
i.putExtra("unfromfood",dataFromGrid);
startActivity(i);
}
});
// get all data from sqlite
Cursor cursor = 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(name, price, image, id));
}
adapter.notifyDataSetChanged();
}
@Override
public void onResume(){
super.onResume();
Cursor cursor = 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(name, price, image, id));
}
adapter.notifyDataSetChanged();
}
//Creating The Options Menu
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
//Option Menu Click Events
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
// Settings
if (id == R.id.action_add_student) {
{
final Intent intent = new Intent();
intent.setClass(Student.this, MainActivity.class);
startActivity(intent);
}
}
return true;
}
}
一切正常，但滚动有滞后，任何帮助都会受到赞赏。
修改
public class AddFood extends AppCompatActivity {
EditText edtName, edtPrice;
Button btnChoose, btnAdd, btnList;
CircularImageView imageView;
final int REQUEST_CODE_GALLERY = 999;
public static SQLiteHelper sqLiteHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_food);
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 BLOB)");
btnChoose.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ActivityCompat.requestPermissions(
AddFood.this,
new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
REQUEST_CODE_GALLERY
);
}
});
//THIS IS WHERE I ADD
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();
finish();
}
catch (Exception e){
e.printStackTrace();
}
}
});
}
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 permission to access file location!", 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.edtName);
edtPrice = (EditText) findViewById(R.id.edtPrice);
btnChoose = (Button) findViewById(R.id.btnChoose);
btnAdd = (Button) findViewById(R.id.btnAdd);
btnList = (Button) findViewById(R.id.btnList);
imageView = (CircularImageView) findViewById(R.id.imageView);
}
}
答案 0 :(得分：1)
要在滚动期间摆脱延迟，您必须有效地加载图像。您可以做的最好的事情是使用像Glide这样的图像加载库。
只需导入库并替换这些行
byte[] foodImage = food.getImage();
Bitmap bitmap = BitmapFactory.decodeByteArray(foodImage, 0, foodImage.length);
holder.imageView.setImageBitmap(bitmap);
这一个
Glide.with(context)
.load(food.getImage())
.into(holder.imageView);
我还建议您阅读Loading Large Bitmaps Efficiently
修改
为了避免回收问题（实际上这不是问题，这是列表视图的工作方式），如果每个项目都有照片，你必须检查它们。
如果是，则使用Glide加载图像，否则设置为null（或您选择的默认图像）。
if (food.getImage() != null && food.getImage().length > 0) {
Glide.with(context)
.load(food.getImage())
.into(holder.imageView);
}
else {
holder.imageView.setImageBitmap(null); //or an image of your choice
}
答案 1 :(得分：0)
试试这个 这个例子将帮助你很多
public class MainActivity extends Activity {
public class ImageAdapter extends BaseAdapter {
private Context mContext;
ArrayList<String> itemList = new ArrayList<String>();
public ImageAdapter(Context c) {
mContext = c;
}
void add(String path){
itemList.add(path);
}
@Override
public int getCount() {
return itemList.size();
}
@Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return null;
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}
Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);
imageView.setImageBitmap(bm);
return imageView;
}
public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth, int reqHeight) {
Bitmap bm = null;
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeFile(path, options);
return bm;
}
public int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float)height / (float)reqHeight);
} else {
inSampleSize = Math.round((float)width / (float)reqWidth);
}
}
return inSampleSize;
}
}
ImageAdapter myImageAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
GridView gridview = (GridView) findViewById(R.id.gridview);
myImageAdapter = new ImageAdapter(this);
gridview.setAdapter(myImageAdapter);
String ExternalStorageDirectoryPath = Environment
.getExternalStorageDirectory()
.getAbsolutePath();
String targetPath = ExternalStorageDirectoryPath + "/test/";
Toast.makeText(getApplicationContext(), targetPath, Toast.LENGTH_LONG).show();
File targetDirector = new File(targetPath);
File[] files = targetDirector.listFiles();
for (File file : files){
myImageAdapter.add(file.getAbsolutePath());
}
}
}