在我的应用程序中,我有一个部分(片段),我想通过ListView显示植物及其数量(存储在Firebase上)。 通过使用浮动操作按钮,我允许更新与工厂相关的数量(如果已经在数据库中),否则添加它。
这是我的前两个问题:
#1 这个片段显示在主要活动中,因此在启动时我希望立即显示从数据库中检索到的数据,但这并不会发生,只有在添加/更新工厂后才会显示它们。
#2 这是我的代码:
public class MyVegGardenFragment extends Fragment {
private View v;
private ListView listView;
private DatabaseReference database;
private FirebaseAuth auth;
private FirebaseUser us;
private Map<String, Integer> myVegGarden;
private ArrayList<String> plantsList = new ArrayList<>();
private ArrayList<Integer> quantityList = new ArrayList<>();
private MyVegGardenAdapter adapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
myVegGarden = new HashMap<>();
database = FirebaseDatabase.getInstance().getReference();
auth = FirebaseAuth.getInstance();
us = auth.getCurrentUser();
database.addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User u = dataSnapshot.child("users").child(us.getUid()).getValue(User.class);
if (u != null) {
myVegGarden = u.getMyVegGarden();
if (myVegGarden != null) {
for(Map.Entry<String, Integer> entry : myVegGarden.entrySet()) {
plantsList.add(entry.getKey());
quantityList.add(entry.getValue());
}
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
v = inflater.inflate(R.layout.myveggarden_fragment_layout, container, false);
listView = (ListView) v.findViewById(R.id.myVegGarden_list_view);
adapter = new MyVegGardenAdapter(getActivity(), plantsList, quantityList);
listView.setAdapter(adapter);
FloatingActionButton fab = (FloatingActionButton) v.findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder;
// [...] leaving code for AlertDialog working correctly
builder.setPositiveButton("PLANT", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
final String plant = options[plant_picker.getValue()];
final int quantity = quantity_picker.getValue();
if(!adapter.getPlantsList().contains(plant)){
adapter.add(plant, quantity);
}
else {
adapter.updateIfPresent(plant, quantity);
}
//update db value
database.addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User u = dataSnapshot.child("users").child(us.getUid()).getValue(User.class);
if (u != null) {
myVegGarden = u.getMyVegGarden();
if (myVegGarden != null) {
myVegGarden.put(plant, quantity);
}
else {
myVegGarden = new HashMap<>();
myVegGarden.put(plant, quantity);
}
database.child("users").child(us.getUid()).child("myVegGarden").setValue(myVegGarden);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
dialog.dismiss();
}
});
builder.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
} });
AlertDialog dialog = builder.create();
dialog.show();
}
});
return v;
}
}
public class MyVegGardenAdapter extends BaseAdapter {
private Context context;
private LayoutInflater inflater;
private ArrayList<String> dataSource;
private ArrayList<Integer> quantity;
public MyVegGardenAdapter(Context context, ArrayList<String> items, ArrayList<Integer> quantity) {
this.context = context;
dataSource = items;
this.quantity = quantity;
//line 31
inflater = (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public void add(String plant, Integer qty) {
dataSource.add(plant);
quantity.add(qty);
notifyDataSetChanged();
}
public void updateIfPresent(String plant, Integer qty) {
quantity.set(dataSource.indexOf(plant), qty);
notifyDataSetChanged();
}
public List<String> getPlantsList() { return dataSource; }
@Override
public int getCount() {
return dataSource.size();
}
@Override
public Object getItem(int position) {
return dataSource.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
public Object getQuantity(int position) {
return quantity.get(position);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// Get view for row item
View rowView = inflater.inflate(R.layout.listview_row, parent, false);
// Get title element
TextView firstLine = (TextView) rowView.findViewById(R.id.firstLine);
// Get subtitle element
TextView secondLine = (TextView) rowView.findViewById(R.id.secondLine);
// Get icon element
ImageView icon = (ImageView) rowView.findViewById(R.id.list_icon);
String plant = (String) getItem(position);
Integer quantity = (Integer) getQuantity(position);
firstLine.setText(plant);
secondLine.setText(Html.fromHtml("<b>Quantity: </b>" + quantity));
switch(plant) {
case "Bean":
icon.setImageResource(R.drawable.ic_bean_48dp); break;
case "Cabbage":
icon.setImageResource(R.drawable.ic_cabbage_48dp); break;
case "Carrot":
icon.setImageResource(R.drawable.ic_carrot_48dp); break;
case "Cucumber":
icon.setImageResource(R.drawable.ic_cucumber_48dp); break;
case "Eggplant":
icon.setImageResource(R.drawable.ic_eggplant_48dp); break;
case "Lettuce":
icon.setImageResource(R.drawable.ic_lettuce_48dp); break;
case "Pea":
icon.setImageResource(R.drawable.ic_pea_48dp); break;
case "Pepper":
icon.setImageResource(R.drawable.ic_pepper_48dp); break;
case "Radish":
icon.setImageResource(R.drawable.ic_radish_48dp); break;
case "Tomato":
icon.setImageResource(R.drawable.ic_tomato_48dp); break;
}
return rowView;
}
}
嗯......数据库总是正确更新,但是:有时plantList和quantityLists会插入副本,因此植物出现两次或三次,我不想要它。
修改 我成功地解决了这两个问题。 现在只有以下问题。通常会发生此错误:
10-19 19:28:52.460 19148-19148 / .veggarden E / AndroidRuntime:致命异常:主要 过程:.veggarden,PID:19148 java.lang.NullPointerException:尝试调用虚方法 &#39; java.lang.Object中 android.content.Context.getSystemService(java.lang.String中)&#39;在null 对象参考 在 .veggarden.MyVegGardenAdapter。(MyVegGardenAdapter.java:31) 在 .veggarden.MyVegGardenFragment $ 1.onDataChange(MyVegGardenFragment.java:85) 在com.google.android.gms.internal.zzbmz.zza(未知来源) 在com.google.android.gms.internal.zzbnz.zzYj(未知来源) 在com.google.android.gms.internal.zzboc $ 1.run(未知来源) 在android.os.Handler.handleCallback(Handler.java:751) 在android.os.Handler.dispatchMessage(Handler.java:95) 在android.os.Looper.loop(Looper.java:154) 在android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) 在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:866) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
到目前为止,这个错误发生了:
这是我的最新代码:
public class MyVegGardenFragment extends Fragment {
private View v;
private ListView listView;
private DatabaseReference database;
private FirebaseAuth auth;
private FirebaseUser us;
private Map<String, Integer> myVegGarden;
private ArrayList<String> plantsList = new ArrayList<>();
private ArrayList<Integer> quantityList = new ArrayList<>();
private MyVegGardenAdapter adapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
myVegGarden = new HashMap<>();
database = FirebaseDatabase.getInstance().getReference();
auth = FirebaseAuth.getInstance();
us = auth.getCurrentUser();
v = inflater.inflate(R.layout.myveggarden_fragment_layout, container, false);
listView = (ListView) v.findViewById(R.id.myVegGarden_list_view);
database.addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
plantsList = new ArrayList<String>();
quantityList = new ArrayList<Integer>();
User u = dataSnapshot.child("users").child(us.getUid()).getValue(User.class);
if (u != null) {
myVegGarden = u.getMyVegGarden();
if (myVegGarden != null) {
for(Map.Entry<String, Integer> entry : myVegGarden.entrySet()) {
plantsList.add(entry.getKey());
quantityList.add(entry.getValue());
}
}
**line 85**
adapter = new MyVegGardenAdapter(getActivity(), plantsList, quantityList);
listView.setAdapter(adapter);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
FloatingActionButton fab = (FloatingActionButton) v.findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder;
// [...] leaving code for AlertDialog working correctly
builder.setPositiveButton("PLANT", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
final String plant = options[plant_picker.getValue()];
final int quantity = quantity_picker.getValue();
if(!adapter.getPlantsList().contains(plant)){
adapter.add(plant, quantity);
}
else {
adapter.updateIfPresent(plant, quantity);
}
if (myVegGarden != null) {
myVegGarden.put(plant, quantity);
database.child("users").child(us.getUid()).child("myVegGarden").setValue(myVegGarden);
}
else {
myVegGarden = new HashMap<String, Integer>();
myVegGarden.put(plant, quantity);
database.child("users").child(us.getUid()).child("myVegGarden").setValue(myVegGarden);
}
dialog.dismiss();
}
});
builder.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
} });
AlertDialog dialog = builder.create();
dialog.show();
}
});
return v;
}
适配器与以前相同。
我希望有人可以帮助我。
答案 0 :(得分:1)
数据检索在Firebase中是异步的,因此您的列表不会立即填充。在检索数据之前,您可以考虑使用类似于“正在加载...”的文本显示ProgressBar或简单TextView。
此外,每次数据更改时,都会调用您提供给addValueEventListener()
的侦听器。
对于第二个问题,我认为你应该做两个调整。第一个是更新addValueEventListener()
中的顶部onCreateView()
:
database.addValueEventListener(new ValueEventListener() {
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User u = dataSnapshot.child("users").child(us.getUid()).getValue(User.class);
if (u != null) {
myVegGarden = u.getMyVegGarden();
if (myVegGarden != null) {
plantsList = new ArrayList<>();
quantityList = new ArrayList<>();
for(Map.Entry<String, Integer> entry : myVegGarden.entrySet()) {
plantsList.add(entry.getKey());
quantityList.add(entry.getValue());
}
adapter.notifyDataSetChanged();
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
第二个调整是简化AlertDialog的onClick()
,如下所示:
@Override
public void onClick(DialogInterface dialog, int which) {
final String plant = options[plant_picker.getValue()];
final int quantity = quantity_picker.getValue();
// Update db value
myVegGarden = new HashMap<>();
myVegGarden.put(plant, quantity);
database.child("users").child(us.getUid()).child("myVegGarden").setValue(myVegGarden);
}
这应该足够了。使用工厂和数量创建地图,setValue()
将其添加到路径中(如果该对不存在)。如果该对存在于该路径中,setValue()
将更新它。此更新将依次调用已调整的addValueEventListener()
,更新plantList和quantityList。
答案 1 :(得分:0)
这对您的代码而言不仅仅是一个问题。 (这里更容易添加代码)。
在onCreateView
方法中,你有这个:
v = inflater.inflate(R.layout.myveggarden_fragment_layout, container, false);
listView = (ListView) v.findViewById(R.id.myVegGarden_list_view);
adapter = new MyVegGardenAdapter(getActivity(), plantsList, quantityList);
listView.setAdapter(adapter);
但是,在设置适配器之前,我没有看到您填充单个ArrayList plantList
或quantityList
的位置?