DataSnapshot

public class DataSnapshot extends Object

A DataSnapshot instance contains data from a Firebase Database location. Any time you read Database data, you receive the data as a DataSnapshot.

DataSnapshots are passed to the methods in listeners that you attach with addValueEventListener(ValueEventListener), addChildEventListener(ChildEventListener), or addListenerForSingleValueEvent(ValueEventListener).

They are efficiently-generated immutable copies of the data at a Firebase Database location. They can't be modified and will never change. To modify data at a location, use a DatabaseReference reference (e.g. with setValue(Object)).

Public Method Summary

DataSnapshot
child(String path)
Get a DataSnapshot for the location at the specified relative path.
boolean
exists()
Returns true if the snapshot contains a non-null value.
Iterable<DataSnapshot>
getChildren()
Gives access to all of the immediate children of this snapshot.
long
String
getKey()
Object
getPriority()
Returns the priority of the data contained in this snapshot as a native type.
DatabaseReference
getRef()
Used to obtain a reference to the source location for this snapshot.
Object
getValue(boolean useExportFormat)
getValue() returns the data contained in this snapshot as native types.
<T> T
getValue(GenericTypeIndicator<T> t)
Due to the way that Java implements generics, it takes an extra step to get back a properly-typed Collection.
Object
getValue()
getValue() returns the data contained in this snapshot as native types.
<T> T
getValue(Class<T> valueType)
This method is used to marshall the data contained in this snapshot into a class of your choosing.
boolean
hasChild(String path)
Can be used to determine if this DataSnapshot has data at a particular location
boolean
hasChildren()
Indicates whether this snapshot has any children
String

Inherited Method Summary

Public Methods

public DataSnapshot child (String path)

Get a DataSnapshot for the location at the specified relative path. The relative path can either be a simple child key (e.g. 'fred') or a deeper slash-separated path (e.g. 'fred/name/first'). If the child location has no data, an empty DataSnapshot is returned.

Parameters
path A relative path to the location of child data
Returns
  • The DataSnapshot for the child location

public boolean exists ()

Returns true if the snapshot contains a non-null value.

Returns
  • True if the snapshot contains a non-null value, otherwise false

public Iterable<DataSnapshot> getChildren ()

Gives access to all of the immediate children of this snapshot. Can be used in native for loops:
for (DataSnapshot child : parent.getChildren()) {
    ...
}

Returns
  • The immediate children of this snapshot

public long getChildrenCount ()

Returns
  • The number of immediate children in the this snapshot

public String getKey ()

Returns
  • the key name for the source location of this snapshot

public Object getPriority ()

Returns the priority of the data contained in this snapshot as a native type. Possible return types:

  • Double
  • String

Note that null is also allowed.

Returns
  • the priority of the data contained in this snapshot as a native type

public DatabaseReference getRef ()

Used to obtain a reference to the source location for this snapshot.

Returns
  • A DatabaseReference corresponding to the location that this snapshot came from

public Object getValue (boolean useExportFormat)

getValue() returns the data contained in this snapshot as native types. The possible types returned are:

  • Boolean
  • String
  • Long
  • Double
  • Map<String, Object>
  • List<Object>

This list is recursive; the possible types for java.lang.Object in the above list is given by the same list. These types correspond to the types available in JSON.

If useExportFormat is set to true, priority information will be included in the output. Priority information shows up as a .priority key in a map. For data that would not otherwise be a map, the map will also include a .value key with the data.

Parameters
useExportFormat Whether or not to include priority information
Returns
  • The data, along with its priority, in native types

public T getValue (GenericTypeIndicator<T> t)

Due to the way that Java implements generics, it takes an extra step to get back a properly-typed Collection. So, in the case where you want a java.util.List of Message instances, you will need to do something like the following:


     GenericTypeIndicator<List<Message>> t = new GenericTypeIndicator<List<
     Message>>()
 {};
     List<Message> messages = snapshot.getValue(t);
 

It is important to use a subclass of GenericTypeIndicator. See GenericTypeIndicator for more details

Parameters
t A subclass of GenericTypeIndicator indicating the type of generic collection to be returned.
Returns
  • A properly typed collection, populated with the data from this snapshot

public Object getValue ()

getValue() returns the data contained in this snapshot as native types. The possible types returned are:

  • Boolean
  • String
  • Long
  • Double
  • Map<String, Object>
  • List<Object>

This list is recursive; the possible types for java.lang.Object in the above list is given by the same list. These types correspond to the types available in JSON.

Returns
  • The data contained in this snapshot as native types

public T getValue (Class<T> valueType)

This method is used to marshall the data contained in this snapshot into a class of your choosing. The class must fit 2 simple constraints:

  1. The class must have a default constructor that takes no arguments
  2. The class must define public getters for the properties to be assigned. Properties without a public getter will be set to their default value when an instance is deserialized

An example class might look like:


     class Message {
         private String author;
         private String text;

         private Message() {}

         public Message(String author, String text) {
             this.author = author;
             this.text = text;
         }

         public String getAuthor() {
             return author;
         }

         public String getText() {
             return text;
         }
     }


     // Later
     Message m = snapshot.getValue(Message.class);
 

Parameters
valueType The class into which this snapshot should be marshalled
Returns
  • An instance of the class passed in, populated with the data from this snapshot

public boolean hasChild (String path)

Can be used to determine if this DataSnapshot has data at a particular location

Parameters
path A relative path to the location of child data
Returns
  • Whether or not the specified child location has data

public boolean hasChildren ()

Indicates whether this snapshot has any children

Returns
  • True if the snapshot has any children, otherwise false

public String toString ()

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