48 lines
2.1 KiB
Kotlin
48 lines
2.1 KiB
Kotlin
package cash.z.ecc.android.sdk.demoapp.preference.model.entry
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import cash.z.ecc.android.sdk.demoapp.preference.api.PreferenceProvider
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import kotlinx.coroutines.flow.Flow
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import kotlinx.coroutines.flow.distinctUntilChanged
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import kotlinx.coroutines.flow.map
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/**
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* An entry represents a key and a default value for a preference. By using a Default object,
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* multiple parts of the code can fetch the same preference without duplication or accidental
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* variation in default value. Clients define the key and default value together, rather than just
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* the key.
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*/
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/*
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* API note: the default value is not available through the public interface in order to prevent
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* clients from accidentally using the default value instead of the preference value.
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*
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* Implementation note: although primitives would be nice, Objects don't increase memory usage much.
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* The autoboxing cache solves Booleans, and Strings are already objects, so that just leaves Integers.
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* Overall the number of Integer preference entries is expected to be low compared to Booleans,
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* and perhaps many Integer values will also fit within the autoboxing cache.
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*/
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interface PreferenceDefault<T> {
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val key: Key
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/**
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* @param preferenceProvider Provides actual preference values.
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* @return The value in the preference, or the default value if no preference exists.
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*/
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suspend fun getValue(preferenceProvider: PreferenceProvider): T
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/**
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* @param preferenceProvider Provides actual preference values.
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* @param newValue New value to write.
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*/
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suspend fun putValue(preferenceProvider: PreferenceProvider, newValue: T)
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/**
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* @param preferenceProvider Provides actual preference values.
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* @return Flow that emits preference changes. Note that implementations should emit an initial value
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* indicating what was stored in the preferences, in addition to subsequent updates.
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*/
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fun observe(preferenceProvider: PreferenceProvider): Flow<T> = preferenceProvider.observe(key)
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.map { getValue(preferenceProvider) }
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.distinctUntilChanged()
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}
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