java.lang.Object | |
↳ | com.google.firebase.database.DataSnapshot |
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 Methods | |||||||||||
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Get a DataSnapshot for the location at the specified relative path.
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Returns true if the snapshot contains a non-null value.
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Gives access to all of the immediate children of this snapshot.
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Returns the priority of the data contained in this snapshot as a native type.
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Used to obtain a reference to the source location for this snapshot.
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getValue() returns the data contained in this snapshot as native types.
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Due to the way that Java implements generics, it takes an extra step to get back a
properly-typed Collection.
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getValue() returns the data contained in this snapshot as native types.
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This method is used to marshall the data contained in this snapshot into a class of your
choosing.
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Can be used to determine if this DataSnapshot has data at a particular location
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Indicates whether this snapshot has any children
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Inherited Methods | |||||||||||
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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 | |
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path |
String :
A relative path to the location of child data |
Returns | |
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DataSnapshot |
The DataSnapshot for the child location |
Returns true if the snapshot contains a non-null value.
Returns | |
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boolean |
True if the snapshot contains a non-null value, otherwise false |
Gives access to all of the immediate children of this snapshot. Can be used in native for
loops:
for (DataSnapshot child : parent.getChildren()) {
...
}
Returns | |
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Iterable<DataSnapshot> |
The immediate children of this snapshot |
Returns | |
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long |
The number of immediate children in the this snapshot |
Returns | |
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String |
the key name for the source location of this snapshot |
Returns the priority of the data contained in this snapshot as a native type. Possible return types:
Returns | |
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Object |
the priority of the data contained in this snapshot as a native type |
Used to obtain a reference to the source location for this snapshot.
Returns | |
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DatabaseReference |
A DatabaseReference corresponding to the location that this snapshot came from |
getValue() returns the data contained in this snapshot as native types. The possible types returned are:
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 | |
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useExportFormat |
boolean :
Whether or not to include priority information |
Returns | |
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Object |
The data in native types, along with its priority, or null if there is no data at this location. |
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 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 | |
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t |
GenericTypeIndicator :
A subclass of GenericTypeIndicator indicating the type of generic collection
to be returned. |
Returns | |
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T |
A properly typed collection, populated with the data from this snapshot, or null if there is no data at this location. |
getValue() returns the data contained in this snapshot as native types. The possible types returned are:
Object
in the above list is
given by the same list. These types correspond to the types available in JSON.
Returns | |
---|---|
Object |
The data contained in this snapshot as native types or null if there is no data at this location. |
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:
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 | |
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valueType |
Class :
The class into which this snapshot should be marshalled |
Returns | |
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T |
An instance of the class passed in, populated with the data from this snapshot, or null if there is no data at this location. |
Can be used to determine if this DataSnapshot has data at a particular location
Parameters | |
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path |
String :
A relative path to the location of child data |
Returns | |
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boolean |
Whether or not the specified child location has data |
Indicates whether this snapshot has any children
Returns | |
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boolean |
True if the snapshot has any children, otherwise false |
Returns | |
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String |