我一直在努力寻找解决我的问题的方法，即我希望从此数据库架构中获取数据
{
"brs" : {
"route": [
{
"routeDestination": "DDDD1",
"routeOrigin": "OOOO1",
"bus" : {
"busArrivalTime" : "created_at_timestamp",
"busDepartureTime" : "created_at_timestamp",
"busName" : "SOME NAME",
"busSeatCost" : "0000",
"busTotalSeats" : "000",
"reservations": [
{
"reservationId": 1,
"reservationDate": "Wed Jul 06 23:54:56 EDT 2016",
"seats": [
{
"seatNumber": 1
},
{
"seatNumber": 2
}
]
}
]
}
},
{
"routeDestination": "DDDD2",
"routeOrigin": "OOOO2",
"bus" : {
"busArrivalTime" : "created_at_timestamp",
"busDepartureTime" : "created_at_timestamp",
"busName" : "SOME NAME",
"busSeatCost" : "0000",
"busTotalSeats" : "000",
"reservations": [
{
"reservationId": 1,
"reservationDate": "Wed Jul 06 23:54:56 EDT 2016",
"seats": [
{
"seatNumber": 1
},
{
"seatNumber": 2
}
]
}
]
}
},
{
"routeDestination": "DDDD3",
"routeOrigin": "OOOO3",
"bus" : {
"busArrivalTime" : "created_at_timestamp",
"busDepartureTime" : "created_at_timestamp",
"busName" : "SOME NAME",
"busSeatCost" : "0000",
"busTotalSeats" : "000",
"reservations": [
{
"reservationId": 1,
"reservationDate": "Wed Jul 06 23:54:56 EDT 2016",
"seats": [
{
"seatNumber": 1
},
{
"seatNumber": 2
}
]
}
]
}
}
]
}
}
使用此代码
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(final View view) {
FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
DatabaseReference myRef = firebaseDatabase.getReference("route");
try {
// Read from the database
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
GenericTypeIndicator<List<String>> t = new GenericTypeIndicator<List<String>> () {};
List<String> routes = dataSnapshot.getValue(t);
if( routes == null ) {
Snackbar.make(view, "Returned No Result" , Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
else {
Snackbar.make(view, "The routes Size is " + routes.size(), Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("BUS_TAG", "Failed to read value.", error.toException());
}
});
} catch (Exception e) {
e.printStackTrace();
}
}
});
通过上面的代码我只得到结果Snack bar说返回无结果。
我按照 @silverFoxA 的建议进行了尝试，并简单地制作了POJO
public class Route {
private String routeDestination;
private String routeOrigin;
public String getRouteDestination() {
return routeDestination;
}
public void setRouteDestination(String routeDestination) {
this.routeDestination = routeDestination;
}
public String getRouteOrigin() {
return routeOrigin;
}
public void setRouteOrigin(String routeOrigin) {
this.routeOrigin = routeOrigin;
}
}
并尝试了以下答案中给出的代码
DatabaseReference myRef = FirebaseDatabase.getInstance().getReference("routes");
Toast.makeText(MainActivity.this, "Clicked ---- ", Toast.LENGTH_LONG).show();
final List<Route> routes = new CopyOnWriteArrayList<Route>();
try {
// Read from the database
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println("The routes Size is " + dataSnapshot.getChildrenCount());
Snackbar.make(view, "The routes Size is " + routes.size(), Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
for (DataSnapshot route : dataSnapshot.getChildren()) {
System.out.println("from " + route.child("routeOrigin").getValue() +
" to " + route.child("routeDestination").getValue());
}
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("BUS_TAG", "Failed to read value.", error.toException());
}
});
现在我得到 的结果路线尺寸为0 。
我也尝试过不同的方式
DatabaseReference myRef = FirebaseDatabase.getInstance().getReference("brs");
Toast.makeText(MainActivity.this, "Clicked ---- ", Toast.LENGTH_LONG).show();
final List<Route> routes = new CopyOnWriteArrayList<Route>();
myRef.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
Route route = dataSnapshot.getValue(Route.class);
routes.add(route);
Snackbar.make(view, "The routes Size is " + routes.size(), Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
此代码导致
的异常07-25 06:26:33.792 5861-5861/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.rhcloud.escot.bsr, PID: 5861
com.google.firebase.database.DatabaseException: Can't convert object of type java.util.ArrayList to type com.rhcloud.escot.bsr.Route
at com.google.android.gms.internal.zzalq.zzd(Unknown Source)
at com.google.android.gms.internal.zzalq.zzb(Unknown Source)
at com.google.android.gms.internal.zzalq.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.rhcloud.escot.bsr.MainActivity$2$2.onChildAdded(MainActivity.java:94)
at com.google.android.gms.internal.zzahh.zza(Unknown Source)
at com.google.android.gms.internal.zzajh.zzctc(Unknown Source)
at com.google.android.gms.internal.zzajk$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
07-25 06:26:33.871 6417-6417/? E/SysUtils: ApplicationContext is null in ApplicationStatus
如何获取路由列表/数组并迭代它，在这种情况下我需要一些帮助。
答案 0 :(得分：1)
尝试使用此db的最后一个解决方案：
DatabaseReference myRef = FirebaseDatabase.getInstance().child("brs").child("route");
or
DatabaseReference myRef = FirebaseDatabase.getInstance().child("brs/route");
答案 1 :(得分：0)
您实际上不太可能在Firebase中存储数组。它更可能是一个关联数组，它们的键可能是整数。
使用Firebase数据库时，通常不使用数组并将所有内容视为Map。在您的情况下，这可以解决您的问题：
public void onDataChange(DataSnapshot snapshot) {
System.out.println("The routes Size is " + snapshot.getNumChildren());
for (DataSnapshot route: snapshot.getChildren()) {
System.out.println("from "+route.child("routeOrigin").getValue()+
" to "+route.child("routeDestination").getValue());
}
}
请参阅Android reference docs中的getChildrenCount()和getChildren()。
正如silverFoxA评论的那样，强烈建议您创建一个表示路由的Java类。处理DataSnapshot或（甚至更糟）类型安全的List或Map实例会迅速推动即使是最顽固的开发人员疯狂。
答案 2 :(得分：0)
DatabaseReference myRef = FirebaseDatabase.getInstance().getReference("routes");
but in your json object its "route".
ArrayList<Route> listRoutes = new ArrayList();
DatabaseReference myRef = FirebaseDatabase.getInstance().getReference("route");
try {
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot routeSnapshot:dataSnapshot.getChildren()){
Route route = routeSnapshot.getValue(Route.class);
//save each route in arraylist
listRoutes.add(route);
}
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w("BUS_TAG", "Failed to read value.", error.toException());
}
});