OperationMonitor.java
/*
* Copyright 2017 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 androidx.recyclerview.selection;
import static androidx.annotation.RestrictTo.Scope.LIBRARY;
import static androidx.core.util.Preconditions.checkArgument;
import static androidx.core.util.Preconditions.checkState;
import static androidx.recyclerview.selection.Shared.DEBUG;
import android.util.Log;
import androidx.annotation.MainThread;
import androidx.annotation.NonNull;
import androidx.annotation.RestrictTo;
import java.util.ArrayList;
import java.util.List;
/**
* OperationMonitor provides a mechanism to coordinate application
* logic with ongoing user selection activities (such as active band selection
* and active gesture selection).
*
* <p>
* The host {@link android.app.Activity} or {@link android.app.Fragment} should avoid changing
* {@link androidx.recyclerview.widget.RecyclerView.Adapter Adapter} data while there
* are active selection operations, as this can result in a poor user experience.
*
* <p>
* To know when an operation is active listen to changes using an {@link OnChangeListener}.
*/
public final class OperationMonitor {
private static final String TAG = "OperationMonitor";
private final List<OnChangeListener> mListeners = new ArrayList<>();
// Ideally OperationMonitor would implement Resettable
// directly, but Metalava couldn't understand that
// `OperationMonitor` was public API while `Resettable` was
// not. This is our klunkuy workaround.
private final Resettable mResettable = new Resettable() {
@Override
public boolean isResetRequired() {
return OperationMonitor.this.isResetRequired();
}
@Override
public void reset() {
OperationMonitor.this.reset();
}
};
private int mNumOps = 0;
@MainThread
synchronized void start() {
mNumOps++;
if (mNumOps == 1) {
notifyStateChanged();
}
if (DEBUG) Log.v(TAG, "Incremented content lock count to " + mNumOps + ".");
}
@MainThread
synchronized void stop() {
if (mNumOps == 0) {
if (DEBUG) Log.w(TAG, "Stop called whith opt count of 0.");
return;
}
mNumOps--;
if (DEBUG) Log.v(TAG, "Decremented content lock count to " + mNumOps + ".");
if (mNumOps == 0) {
notifyStateChanged();
}
}
/** @hide */
@RestrictTo(LIBRARY)
@MainThread
synchronized void reset() {
if (DEBUG) Log.d(TAG, "Received reset request.");
if (mNumOps > 0) {
Log.w(TAG, "Resetting OperationMonitor with " + mNumOps + " active operations.");
}
mNumOps = 0;
notifyStateChanged();
}
/** @hide */
@RestrictTo(LIBRARY)
synchronized boolean isResetRequired() {
return isStarted();
}
/**
* @return true if there are any running operations.
*/
public synchronized boolean isStarted() {
return mNumOps > 0;
}
/**
* Registers supplied listener to be notified when operation status changes.
*/
public void addListener(@NonNull OnChangeListener listener) {
checkArgument(listener != null);
mListeners.add(listener);
}
/**
* Unregisters listener for further notifications.
*/
public void removeListener(@NonNull OnChangeListener listener) {
checkArgument(listener != null);
mListeners.remove(listener);
}
/**
* Allows other selection code to perform a precondition check asserting the state is locked.
*/
void checkStarted(boolean started) {
if (started) {
checkState(mNumOps > 0);
} else {
checkState(mNumOps == 0);
}
}
private void notifyStateChanged() {
for (OnChangeListener l : mListeners) {
l.onChanged();
}
}
/**
* Work around b/139109223.
* @hide
*/
@RestrictTo(LIBRARY)
@NonNull Resettable asResettable() {
return mResettable;
}
/**
* Listen to changes in operation status. Authors should avoid
* changing the Adapter model while there are active operations.
*/
public interface OnChangeListener {
/**
* Called when operation status changes. Call {@link OperationMonitor#isStarted()}
* to determine the current status.
*/
void onChanged();
}
}