【发布时间】：2020-04-17 22:15:28
【问题描述】：
伙计们。
我对编程和 Android 编程完全陌生，我有一个问题。我从 MySQL 数据库中获取图像作为 InputStream。然后我有适配器，我将从数据库中获得的数据加载到相应的对象。万岁，listView 已创建，一切看起来都不错！但是......当我向下/向上滚动时，我的图像消失了。我读过 listView 回收对象，但问题是我不知道/不明白如何解决这个问题：///
请帮帮我！！
SHORT：滚动时列表视图中的图像消失。太多新手不知道如何解决它：/
事件类
public class Event {
private int id;
private String title;
private Date date;
private String place;
private String genre;
private String description;
private Double price;
public Event(int id, String title, Date date, String place, String genre, String description, Double price, InputStream image) {
this.id = id;
this.title = title;
this.date = date;
this.place = place;
this.genre = genre;
this.description = description;
this.price = price;
this.image = image;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
public String getPlace() {
return place;
}
public void setPlace(String place) {
this.place = place;
}
public String getGenre() {
return genre;
}
public void setGenre(String genre) {
this.genre = genre;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
public InputStream getImage() {
return image;
}
public void setImage(InputStream image) {
this.image = image;
}
private InputStream image;
}
适配器类
public class EventAdapter extends BaseAdapter {
LayoutInflater mInflater;
ArrayList<Event> data;
public EventAdapter(Context c, ArrayList<Event> d){
mInflater = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
this.data = d;
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return data.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
// This is where data is assigned to coresponding fields in event_layout
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// Hooks
View view = mInflater.inflate(R.layout.event_layout, null);
TextView eventName = (TextView) view.findViewById(R.id.eventName);
TextView dateYear = (TextView) view.findViewById(R.id.dateYear);
TextView dateDay = (TextView) view.findViewById(R.id.dateDay);
ImageView image = (ImageView) view.findViewById(R.id.eventImage);
// Changing date format
SimpleDateFormat sdf = new SimpleDateFormat("MMM dd yyyy");
String date = sdf.format(data.get(position).getDate());
// Extracting date into seprate vars
String year = date.substring(8);
String day = date.substring(0, 1).toUpperCase() + date.substring(1, 3) + "." + date.substring(4, 7) + "d.";
// making Bitmap from InputStream
Bitmap bmp = BitmapFactory.decodeStream(data.get(position).getImage());
eventName.setText(data.get(position).getTitle());
dateYear.setText(year);
dateDay.setText(day);
image.setImageBitmap(bmp);
return view;
}
}
EventsPage 类
public class EventsPage extends AppCompatActivity {
private EventAdapter eventAdapter;
private Context thisContext;
private ListView eventsListView;
private TextView progressBar;
private ArrayList<Event> events = new ArrayList<Event>();
@RequiresApi(api = Build.VERSION_CODES.M)
@Override
protected void onCreate(Bundle savedInstanceState) {
// Set status bar color to main_green
if(Build.VERSION.SDK_INT >= 21){
Window window = this.getWindow();
window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
window.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
window.setStatusBarColor(this.getResources().getColor(R.color.main_green_color , this.getTheme()));
}
}
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_events_page);
Resources res = getResources();
eventsListView = (ListView) findViewById(R.id.eventsListView);
progressBar = (TextView) findViewById(R.id.progressBar);
thisContext = this;
progressBar.setText("");
GetData data = new GetData();
data.execute("");
}
public class GetData extends AsyncTask<String, String, String> {
private String msg;
private ArrayList<Event> bkc_events = new ArrayList<>();
private ArrayList<Event> tic_events = new ArrayList<>();
@Override
protected void onPreExecute(){
progressBar.setText("Connecting to database...");
}
@RequiresApi(api = Build.VERSION_CODES.N)
@Override
protected String doInBackground(String... strings) {
Connection conn = null;
Statement stmt = null;
try {
Class.forName(DBstrings.JDBC_DRIVER);
conn = DriverManager.getConnection(DBstrings.URL, DBstrings.USERNAME, DBstrings.PASSWORD);
// Get BKC events
stmt = conn.createStatement();
String query = "SELECT * from `bkc_event` ORDER by `date` ASC";
ResultSet res = stmt.executeQuery(query);
while(res.next()){
Event temp = new Event(res.getInt("ID"), res.getString("title"),
res.getDate("date"), res.getString("place"),
res.getString("genre"), res.getString("description"),
res.getDouble("price"), res.getBinaryStream("image"));
this.bkc_events.add(temp);
}
res.close();
// Get TIC events
query = "SELECT * from `tic_event` ORDER by `date` ASC";
res = stmt.executeQuery(query);
while(res.next()){
Event temp = new Event(res.getInt("ID"), res.getString("title"),
res.getDate("date"), res.getString("place"),
res.getString("genre"), res.getString("description"),
res.getDouble("price"), res.getBinaryStream("image"));
tic_events.add(temp);
}
res.close();
stmt.close();
conn.close();
msg = "Process Completed";
PutDataTogether(bkc_events, tic_events);
} catch (ClassNotFoundException ex) {
msg = "Class not found ERROR";
Log.e("ClassNotFound", ex.getMessage());
} catch (SQLException ex) {
msg = "SQL exceltion";
Log.e("SQL:", ex.getMessage());
} finally {
try {
if(stmt != null)
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(conn != null)
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
return null;
}
// Combine data 2 sets into 1 set
@RequiresApi(api = Build.VERSION_CODES.N)
private void PutDataTogether(ArrayList<Event> bkc, ArrayList<Event> tic){
events.addAll(bkc);
for (Event t: tic) {
// counter for showing redundancy
int counter = 0;
for(Event r: events){
// Check if title and date is the same if so - increase counter by 1
if(t.getTitle().toLowerCase().equals(r.getTitle().toLowerCase()) &&
t.getDate().equals(r.getDate()))
counter++;
}
// if counter == 0, then we can add event to final result set
if(counter == 0)
events.add(t);
}
events.sort(Comparator.comparing(Event::getDate));
}
// To show the data
@Override
protected void onPostExecute(String msg){
progressBar.setText(this.msg);
/*new Handler().postDelayed(new Runnable() {
@Override
public void run() {
progressBar.setVisibility(View.INVISIBLE);
}
}, 1500); */
// We have stuff to display
if(events.size() > 0){
eventAdapter = new EventAdapter(thisContext, events);
eventsListView.setAdapter(eventAdapter);
}
}
} // END of GetDataEvents class
} // END of EventsPage
问题：
Picture before scrolling
Picture after scrolling down and then back up
【问题讨论】：
标签： java android database imageview inputstream