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/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.content;
import android.annotation.IntDef;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
/**
* Extended {@link ComponentCallbacks} interface with a new callback for
* finer-grained memory management. This interface is available in all application components
* ({@link android.app.Activity}, {@link android.app.Service},
* {@link ContentProvider}, and {@link android.app.Application}).
*
* <p>You should implement {@link #onTrimMemory} to incrementally release memory based on current
* system constraints. Using this callback to release your resources helps provide a more
* responsive system overall, but also directly benefits the user experience for
* your app by allowing the system to keep your process alive longer. That is,
* if you <em>don't</em> trim your resources based on memory levels defined by this callback,
* the system is more likely to kill your process while it is cached in the least-recently used
* (LRU) list, thus requiring your app to restart and restore all state when the user returns to it.
*
* <p>The values provided by {@link #onTrimMemory} do not represent a single linear progression of
* memory limits, but provide you different types of clues about memory availability:</p>
* <ul>
* <li>When your app is running:
* <ol>
* <li>{@link #TRIM_MEMORY_RUNNING_MODERATE} <br>The device is beginning to run low on memory.
* Your app is running and not killable.
* <li>{@link #TRIM_MEMORY_RUNNING_LOW} <br>The device is running much lower on memory.
* Your app is running and not killable, but please release unused resources to improve system
* performance (which directly impacts your app's performance).
* <li>{@link #TRIM_MEMORY_RUNNING_CRITICAL} <br>The device is running extremely low on memory.
* Your app is not yet considered a killable process, but the system will begin killing
* background processes if apps do not release resources, so you should release non-critical
* resources now to prevent performance degradation.
* </ol>
* </li>
* <li>When your app's visibility changes:
* <ol>
* <li>{@link #TRIM_MEMORY_UI_HIDDEN} <br>Your app's UI is no longer visible, so this is a good
* time to release large resources that are used only by your UI.
* </ol>
* </li>
* <li>When your app's process resides in the background LRU list:
* <ol>
* <li>{@link #TRIM_MEMORY_BACKGROUND} <br>The system is running low on memory and your process is
* near the beginning of the LRU list. Although your app process is not at a high risk of being
* killed, the system may already be killing processes in the LRU list, so you should release
* resources that are easy to recover so your process will remain in the list and resume
* quickly when the user returns to your app.
* <li>{@link #TRIM_MEMORY_MODERATE} <br>The system is running low on memory and your process is
* near the middle of the LRU list. If the system becomes further constrained for memory, there's a
* chance your process will be killed.
* <li>{@link #TRIM_MEMORY_COMPLETE} <br>The system is running low on memory and your process is
* one of the first to be killed if the system does not recover memory now. You should release
* absolutely everything that's not critical to resuming your app state.
* <p>To support API levels lower than 14, you can use the {@link #onLowMemory} method as a
* fallback that's roughly equivalent to the {@link ComponentCallbacks2#TRIM_MEMORY_COMPLETE} level.
* </li>
* </ol>
* <p class="note"><strong>Note:</strong> When the system begins
* killing processes in the LRU list, although it primarily works bottom-up, it does give some
* consideration to which processes are consuming more memory and will thus provide more gains in
* memory if killed. So the less memory you consume while in the LRU list overall, the better
* your chances are to remain in the list and be able to quickly resume.</p>
* </li>
* </ul>
* <p>More information about the different stages of a process lifecycle (such as what it means
* to be placed in the background LRU list) is provided in the <a
* href="{@docRoot}guide/components/processes-and-threads.html#Lifecycle">Processes and Threads</a>
* document.
*/
public interface ComponentCallbacks2 extends ComponentCallbacks {
/** @hide */
@IntDef(prefix = { "TRIM_MEMORY_" }, value = {
TRIM_MEMORY_COMPLETE,
TRIM_MEMORY_MODERATE,
TRIM_MEMORY_BACKGROUND,
TRIM_MEMORY_UI_HIDDEN,
TRIM_MEMORY_RUNNING_CRITICAL,
TRIM_MEMORY_RUNNING_LOW,
TRIM_MEMORY_RUNNING_MODERATE,
})
@Retention(RetentionPolicy.SOURCE)
public @interface TrimMemoryLevel {}
/**
* Level for {@link #onTrimMemory(int)}: the process is nearing the end
* of the background LRU list, and if more memory isn't found soon it will
* be killed.
*/
static final int TRIM_MEMORY_COMPLETE = 80;
/**
* Level for {@link #onTrimMemory(int)}: the process is around the middle
* of the background LRU list; freeing memory can help the system keep
* other processes running later in the list for better overall performance.
*/
static final int TRIM_MEMORY_MODERATE = 60;
/**
* Level for {@link #onTrimMemory(int)}: the process has gone on to the
* LRU list. This is a good opportunity to clean up resources that can
* efficiently and quickly be re-built if the user returns to the app.
*/
static final int TRIM_MEMORY_BACKGROUND = 40;
/**
* Level for {@link #onTrimMemory(int)}: the process had been showing
* a user interface, and is no longer doing so. Large allocations with
* the UI should be released at this point to allow memory to be better
* managed.
*/
static final int TRIM_MEMORY_UI_HIDDEN = 20;
/**
* Level for {@link #onTrimMemory(int)}: the process is not an expendable
* background process, but the device is running extremely low on memory
* and is about to not be able to keep any background processes running.
* Your running process should free up as many non-critical resources as it
* can to allow that memory to be used elsewhere. The next thing that
* will happen after this is {@link #onLowMemory()} called to report that
* nothing at all can be kept in the background, a situation that can start
* to notably impact the user.
*/
static final int TRIM_MEMORY_RUNNING_CRITICAL = 15;
/**
* Level for {@link #onTrimMemory(int)}: the process is not an expendable
* background process, but the device is running low on memory.
* Your running process should free up unneeded resources to allow that
* memory to be used elsewhere.
*/
static final int TRIM_MEMORY_RUNNING_LOW = 10;
/**
* Level for {@link #onTrimMemory(int)}: the process is not an expendable
* background process, but the device is running moderately low on memory.
* Your running process may want to release some unneeded resources for
* use elsewhere.
*/
static final int TRIM_MEMORY_RUNNING_MODERATE = 5;
/**
* Called when the operating system has determined that it is a good
* time for a process to trim unneeded memory from its process. This will
* happen for example when it goes in the background and there is not enough
* memory to keep as many background processes running as desired. You
* should never compare to exact values of the level, since new intermediate
* values may be added -- you will typically want to compare if the value
* is greater or equal to a level you are interested in.
*
* <p>To retrieve the processes current trim level at any point, you can
* use {@link android.app.ActivityManager#getMyMemoryState
* ActivityManager.getMyMemoryState(RunningAppProcessInfo)}.
*
* @param level The context of the trim, giving a hint of the amount of
* trimming the application may like to perform.
*/
void onTrimMemory(@TrimMemoryLevel int level);
}
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