60 lines
1.8 KiB
Java
60 lines
1.8 KiB
Java
/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.internal.infra;
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import android.annotation.NonNull;
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import android.util.SparseArray;
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import com.android.internal.util.Preconditions;
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/**
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* A {@link SparseArray} customized for a common use-case of storing state per-user.
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*
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* Unlike a normal {@link SparseArray} this will always create a value on {@link #get} if one is
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* not present instead of returning null.
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*
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* @param <T> user state type
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*/
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public abstract class PerUser<T> extends SparseArray<T> {
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/**
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* Initialize state for the given user
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*/
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protected abstract @NonNull T create(int userId);
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/**
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* Same as {@link #get(int)}, renamed for readability.
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*
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* This will never return null, deferring to {@link #create} instead
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* when called for the first time.
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*/
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public @NonNull T forUser(int userId) {
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return get(userId);
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}
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@Override
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public @NonNull T get(int userId) {
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T userState = super.get(userId);
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if (userState != null) {
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return userState;
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} else {
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userState = Preconditions.checkNotNull(create(userId));
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put(userId, userState);
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return userState;
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}
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}
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}
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