在我的应用中，我的用户正在输入类别，该类别存储在 FirebseDB 中。将值存储在DB中后，用户可以在Spinner中查看插入的值。
此时一切正常。
我希望用户只输入唯一值。所以，如果用户想要输入已经存在的值，他应该得到一个Toast。
以下是我的activity_main.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
tools:context="com.example.lenovo.baicactivitytest.MainActivity">
<Spinner
android:id="@+id/sp"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<Button
android:id="@+id/add_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="70dp"
android:text="Add" />
</RelativeLayout>
以下是我的inputdialogue.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:layout_marginTop="?attr/actionBarSize"
android:orientation="vertical"
android:paddingLeft="15dp"
android:paddingRight="15dp"
android:paddingTop="50dp">
<android.support.design.widget.TextInputLayout
android:id="@+id/nameLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<EditText
android:id="@+id/nameEditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:singleLine="true"
android:hint= "Name" />
</android.support.design.widget.TextInputLayout>
<Button android:id="@+id/saveBtn"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Save"
android:clickable="true"
android:background="@color/colorAccent"
android:layout_marginTop="40dp"
android:textColor="@android:color/white"/>
</LinearLayout>
</LinearLayout>
package com.example.lenovo.baicactivitytest;
/**
* Created by LENOVO on 29-12-2017.
*/
public class Spacecraft {
String name;
public Spacecraft() {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
package com.example.lenovo.baicactivitytest;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseException;
import com.google.firebase.database.DatabaseReference;
import java.util.ArrayList;
/**
* Created by LENOVO on 29-12-2017.
*/
public class FirebaseHelper {
DatabaseReference db;
Boolean saved = null;
public FirebaseHelper(DatabaseReference db) {
this.db = db;
}
//SAVE
public Boolean save(Spacecraft spacecraft)
{
if(spacecraft==null)
{
saved=false;
}else
{
try
{
db.child("Spacecraft").push().setValue(spacecraft);
saved=true;
}catch (DatabaseException e)
{
e.printStackTrace();
saved=false;
}
}
return saved;
}
//READ
public ArrayList<String> retrieve()
{
final ArrayList<String> spacecrafts=new ArrayList<>();
db.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot,spacecrafts);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot,spacecrafts);
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
return spacecrafts;
}
private void fetchData(DataSnapshot snapshot,ArrayList<String> spacecrafts)
{
spacecrafts.clear();
for (DataSnapshot ds:snapshot.getChildren())
{
String name=ds.getValue(Spacecraft.class).getName();
spacecrafts.add(name);
}
}
}
package com.example.lenovo.baicactivitytest;
import android.app.Dialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
public class MainActivity extends AppCompatActivity {
DatabaseReference db;
FirebaseHelper helper;
private Button madd_btn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Spinner sp =(Spinner) findViewById(R.id.sp);
//SETUP FB
db= FirebaseDatabase.getInstance().getReference();
helper = new FirebaseHelper(db);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,helper.retrieve());
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp.setAdapter(adapter);
madd_btn = (Button) findViewById(R.id.add_btn);
madd_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
displayInputDialog();
}
});
}
//DISPLAY INPUT DILAOG
private void displayInputDialog()
{
Dialog d=new Dialog(this);
d.setTitle("Firebase database");
d.setContentView(R.layout.inputdialog);
final EditText nameTxt= (EditText) d.findViewById(R.id.nameEditText);
Button saveBtn = (Button) d.findViewById(R.id.saveBtn);
//SAVE
saveBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//GET DATA
String name=nameTxt.getText().toString();
//set data
Spacecraft s = new Spacecraft();
s.setName(name);
//SAVE
if(name != null && name.length()>0)
{
if(helper.save(s))
{
nameTxt.setText("");
}
}else
{
Toast.makeText(MainActivity.this, "Name Cannot Be Empty", Toast.LENGTH_SHORT).show();
}
}
});
d.show();
}
}
答案 0 :(得分：1)
可以这样做：
DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("Category");
ref.orderByChild("categoryname").equalTo(name).addValueEventListener(new ValueEventListener(){
@Override
public void onDataChange(DataSnapshot dataSnapshot){
if(dataSnapshot.exist()) {
Toast.makeText(MainActivity.this, "Name already exists", Toast.LENGTH_SHORT).show();
}
}
可以执行上述操作，它将在db中的Category节点中进行搜索，如果存在，则会向您提供Toast消息。