[英]How to retrieve items from a database list based on specified criteria
我正在開發一個 android 賬單管理應用程序,並希望將一些指定的數據檢索到一個 android 列表視圖。
我將 valueEventListener 用於此任務,但仍然無法檢索數據。 如何使用 valueEventListener 將這些數據獲取到列表視圖?
XML
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
tools:context=".SubmitReading">
<android.support.v7.widget.Toolbar
android:id="@+id/sr_toolbar1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize"
android:theme="?attr/actionBarTheme"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="12dp"
android:layout_marginBottom="8dp"
android:fontFamily="@font/notosans_bold"
android:text="Submit a Reading"
android:textColor="@color/colorAccent"
android:textSize="70px"
app:layout_constraintBottom_toBottomOf="@+id/sr_toolbar1"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0" />
<ImageButton
android:id="@+id/bt_submit_a_reading_back"
android:layout_width="52dp"
android:layout_height="56dp"
android:background="@null"
android:foreground="?attr/selectableItemBackground"
android:src="@drawable/ic_arrow_back_black_24dp"
app:layout_constraintEnd_toStartOf="@+id/textView3"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="@+id/sr_toolbar1"
app:layout_constraintTop_toTopOf="parent" />
<LinearLayout
android:id="@+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:orientation="horizontal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/sr_toolbar1">
<SearchView
android:id="@+id/search_address"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:queryHint="Search here">
</SearchView>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="68dp"
android:layout_marginEnd="8dp"
android:orientation="horizontal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/linearLayout">
<ListView
android:id="@+id/list_address"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</ListView>
</LinearLayout>
</android.support.constraint.ConstraintLayout>
爪哇
package com.ceb.meterreaderassistant;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import java.util.ArrayList;
public class SubmitReading extends AppCompatActivity {
private ListView listView;
private FirebaseDatabase cebDb;
private DatabaseReference dbRef;
private ArrayList<String> arrayList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_submit_reading);
cebDb = FirebaseDatabase.getInstance();
dbRef = cebDb.getReference("clients");
listView = (ListView)findViewById(R.id.list_address);
final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arrayList);
listView.setAdapter(arrayAdapter);
}
}
我希望查詢的輸出在列表視圖中獲取 clientAddress 數據,目前我沒有得到所需的輸出
您需要執行以下操作:
cebDb = FirebaseDatabase.getInstance();
dbRef = cebDb.getReference("clients");
dmyRef.addValueEventListener( new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot){
if(dataSnapshot.exists()){
for(DataSnapshot ds : dataSnapshot.getChildren()){
String address = ds.child("clientAddress").getValue(String.class);
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
您需要附加ValueEventListener
,然后在直接子級內部進行迭代才能檢索客戶端地址。
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