列表视图不显示来自firebase数据库的任何内容
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数据很容易添加到firebase数据库中，但在列表视图中获取。请帮助activity_1（主要活动）
public class activity_1 extends AppCompatActivity {
private Button b1, b2,b3,submit,list;
private LinearLayout l1,l2,l3;
private DatabaseReference Poll_data,Poll_data_3,Poll_data_4;
private EditText question,desp,edit_option1,edit_option2,edit_option3,edit_option4;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_1);
b1 = (Button) findViewById(R.id.poll_butn2);
b2 = (Button) findViewById(R.id.poll_butn3);
b3 = (Button) findViewById(R.id.poll_butn4);
submit = (Button) findViewById(R.id.poll_submit_button);
list = (Button) findViewById(R.id.poll_submit_button2);
Poll_data = FirebaseDatabase.getInstance().getReference("POll").child("poll_2");
Poll_data_3 = FirebaseDatabase.getInstance().getReference("POll").child("poll_3");
Poll_data_4 = FirebaseDatabase.getInstance().getReference("POll").child("poll_4");
question = (EditText) findViewById(R.id.poll_editque);
edit_option1 = (EditText) findViewById(R.id.option1edit);
desp = (EditText) findViewById(R.id.descp_edit);
edit_option2 = (EditText) findViewById(R.id.option2edit);
edit_option3 = (EditText) findViewById(R.id.option3edit);
edit_option4 = (EditText) findViewById(R.id.option4edit);
l1 = (LinearLayout) findViewById(R.id.poll_option1layout);
l2 = (LinearLayout) findViewById(R.id.poll_option2layout);
l3 = (LinearLayout) findViewById(R.id.poll_option3layout);
l1.setVisibility(l1.INVISIBLE);
l2.setVisibility(l1.INVISIBLE);
l3.setVisibility(l1.INVISIBLE);
b1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
l1.setVisibility(View.VISIBLE);
l2.setVisibility(View.GONE);
l3.setVisibility(View.GONE);
}
});
b2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
l1.setVisibility(View.VISIBLE);
l2.setVisibility(View.VISIBLE);
l3.setVisibility(View.GONE);}
});
b3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
l1.setVisibility(View.VISIBLE);
l2.setVisibility(View.VISIBLE);
l3.setVisibility(View.VISIBLE);}
});
submit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
validate();
}
});
list.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity( new Intent(activity_1.this,listview_activity.class));
}
});
}
private void validate() {
String que = question.getText().toString().trim();
String des = desp.getText().toString().trim();
String option1_2 = edit_option1.getText().toString().trim();
String option2_2 = edit_option2.getText().toString().trim();
String option3_2 = edit_option3.getText().toString().trim();
String option4_2 = edit_option4.getText().toString().trim();
if (!TextUtils.isEmpty(que)) {
if (!TextUtils.isEmpty(option1_2)) {
if (!TextUtils.isEmpty(option2_2)) {
if (TextUtils.isEmpty(option4_2)) {
if (TextUtils.isEmpty(option3_2)) {
String id = Poll_data.push().getKey();
addpoll_2 poll2 = new addpoll_2(id, que, des, option1_2, option2_2);
Poll_data.child(id).setValue(poll2);
Toast.makeText(this, "added", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "option 3 working", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(this, "option 4 working", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(this, "option 2 enter", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(this, "enter option1", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(this, "question compulsory", Toast.LENGTH_SHORT).show();
}
}
}
add poll_2.Java
public class addpoll_2 {
String id;
String question;
String description;
String option_1;
String option_2;
public addpoll_2(String id, String question, String description, String
option_1, String option_2) {
this.id = id;
this.question = question;
this.description = description;
this.option_1 = option_1;
this.option_2 = option_2;
}
public String getId() {
return id;
}
public String getQuestion() {
return question;
}
public String getDescription() {
return description;
}
public String getOption_1() {
return option_1;
}
public String getOption_2() {
return option_2;
}
}
ListView_activity.Java
public class listview_activity extends AppCompatActivity {
ListView listviewpoll;
private DatabaseReference Poll_data;
List<addpoll_2> addpoll_2List;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_listview_activity);
listviewpoll = (ListView) findViewById(R.id.poll_listview);
Poll_data = FirebaseDatabase.getInstance().getReference("POLL");
addpoll_2List = new ArrayList<>();
}
@Override
protected void onStart() {
super.onStart();
Poll_data.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot pollSnapshot: dataSnapshot.getChildren())
{
addpoll_2List.clear();
addpoll_2 poll = pollSnapshot.getValue(addpoll_2.class);
addpoll_2List.add(poll);
}
poll_list adapter = new
poll_list(listview_activity.this,addpoll_2List);
listviewpoll.setAdapter(adapter);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
poll_list.Java
public class poll_list extends ArrayAdapter<addpoll_2> {
private Activity context;
private List<addpoll_2> addpoll_2List ;
public poll_list(Activity context,List<addpoll_2>addpoll_2List){
super(context ,R.layout.list_layout,addpoll_2List);
this.context =context;
this.addpoll_2List = addpoll_2List;
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull
ViewGroup parent) {
LayoutInflater inflater = context.getLayoutInflater();
View viewItem = inflater.inflate(R.layout.list_layout,null,true);
TextView textViewName = (TextView) viewItem.findViewById(R.id.tv);
TextView textViewDesp = (TextView) viewItem.findViewById(R.id.tv1);
addpoll_2 poll = addpoll_2List.get(position);
textViewName.setText(poll.getQuestion());
textViewDesp.setText(poll.getDescription());
return viewItem;
}
}
list_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/linearview"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="@dimen/activity_horizontal_margin">
<TextView
android:id="@+id/tv"
android:textSize="25dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tv1"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
这是所有文件，请检查并回复这些都是详细信息，如果你反对其他，请回复，因为我是android的新手。
答案
你一直在清理清单：
for (DataSnapshot pollSnapshot: dataSnapshot.getChildren()) {
addpoll_2List.clear();
addpoll_2 poll = pollSnapshot.getValue(addpoll_2.class);
addpoll_2List.add(poll);
}
尝试将清除移出for循环：
addpoll_2List.clear();
for (DataSnapshot pollSnapshot: dataSnapshot.getChildren()) {
addpoll_2 poll = pollSnapshot.getValue(addpoll_2.class);
addpoll_2List.add(poll);
}
编辑：
Firebase需要一个空（默认）构造函数才能解析POJO，将其添加到模型类中：
public addpoll_2() {
}
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