SavedStateHandle
class SavedStateHandle
| kotlin.Any | |
| ↳ | androidx.lifecycle.SavedStateHandle |
A handle to saved state passed down to androidx.lifecycle.ViewModel. You should use SavedStateViewModelFactory if you want to receive this object in ViewModel's constructor.
This is a key-value map that will let you write and retrieve objects to and from the saved state. These values will persist after the process is killed by the system and remain available via the same object.
You can read a value from it via get(String) or observe it via androidx.lifecycle.LiveData returned by getLiveData(String).
You can write a value to it via set(String, Object) or setting a value to androidx.lifecycle.MutableLiveData returned by getLiveData(String).
Summary
| Public constructors | |
|---|---|
<init>(@NonNull initialState: MutableMap<String!, Any!>)Creates a handle with the given initial arguments. |
|
<init>()Creates a handle with the empty state. |
|
| Public methods | |
|---|---|
| Unit |
clearSavedStateProvider(@NonNull key: String)Clear any |
| Boolean | |
| T? |
Returns a value associated with the given key. |
| MutableLiveData<T> |
getLiveData(@NonNull key: String)Returns a |
| MutableLiveData<T> |
getLiveData(@NonNull key: String, initialValue: T)Returns a |
| MutableSet<String!> |
keys()Returns all keys contained in this |
| T? |
Removes a value associated with the given key. |
| Unit |
Associate the given value with the key. |
| Unit |
setSavedStateProvider(@NonNull key: String, @NonNull provider: SavedStateRegistry.SavedStateProvider)Set a |
Public constructors
<init>
SavedStateHandle(@NonNull initialState: MutableMap<String!, Any!>)
Creates a handle with the given initial arguments.
<init>
SavedStateHandle()
Creates a handle with the empty state.
Public methods
clearSavedStateProvider
@MainThread fun clearSavedStateProvider(@NonNull key: String): Unit
Clear any SavedStateProvider that was previously set via setSavedStateProvider(String, SavedStateProvider). Note: calling this method within SavedStateProvider#saveState() is supported, but will only affect future state saving operations.
| Parameters | |
|---|---|
key |
String: a key previously used with setSavedStateProvider |
contains
@MainThread fun contains(@NonNull key: String): Boolean
| Return | |
|---|---|
Boolean |
true if there is value associated with the given key. |
get
@MainThread @Nullable fun <T : Any!> get(@NonNull key: String): T?
Returns a value associated with the given key.
getLiveData
@MainThread @NonNull fun <T : Any!> getLiveData(@NonNull key: String): MutableLiveData<T>
Returns a androidx.lifecycle.LiveData that access data associated with the given key.
See Also
getLiveData
@MainThread @NonNull fun <T : Any!> getLiveData(
@NonNull key: String,
initialValue: T
): MutableLiveData<T>
Returns a androidx.lifecycle.LiveData that access data associated with the given key.
<code>LiveData<String> liveData = savedStateHandle.get(KEY, "defaultValue");
</code>
LiveData can have null as a valid value. If the initialValue is null and the data does not already exist in the SavedStateHandle, the value of the returned LiveData will be set to null and observers will be notified. You can call getLiveData(String) if you want to avoid dispatching null to observers.
<code>String defaultValue = ...; // nullable
LiveData<String> liveData;
if (defaultValue != null) {
liveData = savedStateHandle.getLiveData(KEY, defaultValue);
} else {
liveData = savedStateHandle.getLiveData(KEY);
}
</code>
| Parameters | |
|---|---|
key |
String: The identifier for the value |
initialValue |
T: If no value exists with the given key, a new one is created with the given initialValue. Note that passing null will create a LiveData with null value. |
keys
@MainThread @NonNull fun keys(): MutableSet<String!>
Returns all keys contained in this SavedStateHandle
Returned set contains all keys: keys used to get LiveData-s, to set SavedStateProviders and keys used in regular set(String, Object).
remove
@MainThread @Nullable fun <T : Any!> remove(@NonNull key: String): T?
Removes a value associated with the given key. If there is a LiveData associated with the given key, it will be removed as well.
All changes to androidx.lifecycle.LiveData previously returned by SavedStateHandle#getLiveData(String) won't be reflected in the saved state. Also that LiveData won't receive any updates about new values associated by the given key.
| Parameters | |
|---|---|
key |
String: a key |
| Return | |
|---|---|
T? |
a value that was previously associated with the given key. |
set
@MainThread fun <T : Any!> set(
@NonNull key: String,
@Nullable value: T?
): Unit
Associate the given value with the key. The value must have a type that could be stored in android.os.Bundle
| Parameters | |
|---|---|
<T> |
any type that can be accepted by Bundle. |
setSavedStateProvider
@MainThread fun setSavedStateProvider(
@NonNull key: String,
@NonNull provider: SavedStateRegistry.SavedStateProvider
): Unit
Set a SavedStateProvider that will have its state saved into this SavedStateHandle. This provides a mechanism to lazily provide the Bundle of saved state for the given key.
Calls to get with this same key will return the previously saved state as a Bundle if it exists.
Bundle previousState = savedStateHandle.get("custom_object");
if (previousState != null) {
// Convert the previousState into your custom object
}
savedStateHandle.setSavedStateProvider("custom_object", () -> {
Bundle savedState = new Bundle();
// Put your custom object into the Bundle, doing any conversion required
return savedState;
});
Note: calling this method within SavedStateProvider#saveState() is supported, but will only affect future state saving operations.
| Parameters | |
|---|---|
key |
String: a key which will populated with a Bundle produced by the provider |
provider |
SavedStateRegistry.SavedStateProvider: a SavedStateProvider which will receive a callback to SavedStateProvider#saveState() when the state should be saved |