android Loader

安卓学习之路之Loader的简单用法

一、看看loader包目录结构：

 

 

1、LoaderManager

/*
 * Copyright 2018 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.loader.app;

import android.os.Bundle;

import androidx.annotation.MainThread;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.ViewModelStoreOwner;
import androidx.loader.content.Loader;

import java.io.FileDescriptor;
import java.io.PrintWriter;

/**
 * Static library support version of the framework's {@link android.app.LoaderManager}.
 * Used to write apps that run on platforms prior to Android 3.0.  When running
 * on Android 3.0 or above, this implementation is still used; it does not try
 * to switch to the framework's implementation.  See the framework SDK
 * documentation for a class overview.
 *
 * <p>Your activity must derive from {@link androidx.fragment.app.FragmentActivity} to use this.
 */
public abstract class LoaderManager {
    /**
     * Callback interface for a client to interact with the manager.
     */
    public interface LoaderCallbacks<D> {
        /**
         * Instantiate and return a new Loader for the given ID.
         *
         * <p>This will always be called from the process's main thread.
         *
         * @param id The ID whose loader is to be created.
         * @param args Any arguments supplied by the caller.
         * @return Return a new Loader instance that is ready to start loading.
         */
        @MainThread
        @NonNull
        Loader<D> onCreateLoader(int id, @Nullable Bundle args);

        /**
         * Called when a previously created loader has finished its load.  Note
         * that normally an application is <em>not</em> allowed to commit fragment
         * transactions while in this call, since it can happen after an
         * activity's state is saved.  See {@link androidx.fragment.app.FragmentManager#beginTransaction()
         * FragmentManager.openTransaction()} for further discussion on this.
         *
         * <p>This function is guaranteed to be called prior to the release of
         * the last data that was supplied for this Loader.  At this point
         * you should remove all use of the old data (since it will be released
         * soon), but should not do your own release of the data since its Loader
         * owns it and will take care of that.  The Loader will take care of
         * management of its data so you don't have to.  In particular:
         *
         * <ul>
         * <li> <p>The Loader will monitor for changes to the data, and report
         * them to you through new calls here.  You should not monitor the
         * data yourself.  For example, if the data is a {@link android.database.Cursor}
         * and you place it in a {@link android.widget.CursorAdapter}, use
         * the {@link android.widget.CursorAdapter#CursorAdapter(android.content.Context,
         * android.database.Cursor, int)} constructor <em>without</em> passing
         * in either {@link android.widget.CursorAdapter#FLAG_AUTO_REQUERY}
         * or {@link android.widget.CursorAdapter#FLAG_REGISTER_CONTENT_OBSERVER}
         * (that is, use 0 for the flags argument).  This prevents the CursorAdapter
         * from doing its own observing of the Cursor, which is not needed since
         * when a change happens you will get a new Cursor throw another call
         * here.
         * <li> The Loader will release the data once it knows the application
         * is no longer using it.  For example, if the data is
         * a {@link android.database.Cursor} from a {@link android.content.CursorLoader},
         * you should not call close() on it yourself.  If the Cursor is being placed in a
         * {@link android.widget.CursorAdapter}, you should use the
         * {@link android.widget.CursorAdapter#swapCursor(android.database.Cursor)}
         * method so that the old Cursor is not closed.
         * </ul>
         *
         * <p>This will always be called from the process's main thread.
         *
         * @param loader The Loader that has finished.
         * @param data The data generated by the Loader.
         */
        @MainThread
        void onLoadFinished(@NonNull Loader<D> loader, D data);

        /**
         * Called when a previously created loader is being reset, and thus
         * making its data unavailable.  The application should at this point
         * remove any references it has to the Loader's data.
         *
         * <p>This will always be called from the process's main thread.
         *
         * @param loader The Loader that is being reset.
         */
        @MainThread
        void onLoaderReset(@NonNull Loader<D> loader);
    }

    /**
     * Gets a LoaderManager associated with the given owner, such as a {@link androidx.fragment.app.FragmentActivity} or
     * {@link androidx.fragment.app.Fragment}.
     *
     * @param owner The owner that should be used to create the returned LoaderManager
     * @param <T> A class that maintains its own {@link android.arch.lifecycle.Lifecycle} and
     *           {@link android.arch.lifecycle.ViewModelStore}. For instance,
     *           {@link androidx.fragment.app.FragmentActivity} or {@link androidx.fragment.app.Fragment}.
     * @return A valid LoaderManager
     */
    @NonNull
    public static <T extends LifecycleOwner & ViewModelStoreOwner> LoaderManager getInstance(
            @NonNull T owner) {
        return new LoaderManagerImpl(owner, owner.getViewModelStore());
    }

    /**
     * Ensures a loader is initialized and active.  If the loader doesn't
     * already exist, one is created and (if the activity/fragment is currently
     * started) starts the loader.  Otherwise the last created
     * loader is re-used.
     *
     * <p>In either case, the given callback is associated with the loader, and
     * will be called as the loader state changes.  If at the point of call
     * the caller is in its started state, and the requested loader
     * already exists and has generated its data, then
     * callback {@link LoaderCallbacks#onLoadFinished} will
     * be called immediately (inside of this function), so you must be prepared
     * for this to happen.
     *
     * <p>Must be called from the process's main thread.
     *
     * @param id A unique identifier for this loader.  Can be whatever you want.
     * Identifiers are scoped to a particular LoaderManager instance.
     * @param args Optional arguments to supply to the loader at construction.
     * If a loader already exists (a new one does not need to be created), this
     * parameter will be ignored and the last arguments continue to be used.
     * @param callback Interface the LoaderManager will call to report about
     * changes in the state of the loader.  Required.
     */
    @MainThread
    @NonNull
    public abstract <D> Loader<D> initLoader(int id, @Nullable Bundle args,
            @NonNull LoaderManager.LoaderCallbacks<D> callback);

    /**
     * Starts a new or restarts an existing {@link android.content.Loader} in
     * this manager, registers the callbacks to it,
     * and (if the activity/fragment is currently started) starts loading it.
     * If a loader with the same id has previously been
     * started it will automatically be destroyed when the new loader completes
     * its work. The callback will be delivered before the old loader
     * is destroyed.
     *
     * <p>Must be called from the process's main thread.
     *
     * @param id A unique identifier for this loader.  Can be whatever you want.
     * Identifiers are scoped to a particular LoaderManager instance.
     * @param args Optional arguments to supply to the loader at construction.
     * @param callback Interface the LoaderManager will call to report about
     * changes in the state of the loader.  Required.
     */
    @MainThread
    @NonNull
    public abstract <D> Loader<D> restartLoader(int id, @Nullable Bundle args,
            @NonNull LoaderManager.LoaderCallbacks<D> callback);

    /**
     * Stops and removes the loader with the given ID.  If this loader
     * had previously reported data to the client through
     * {@link LoaderCallbacks#onLoadFinished(Loader, Object)}, a call
     * will be made to {@link LoaderCallbacks#onLoaderReset(Loader)}.
     *
     * <p>Must be called from the process's main thread.
     */
    @MainThread
    public abstract void destroyLoader(int id);

    /**
     * Return the Loader with the given id or null if no matching Loader
     * is found.
     */
    @Nullable
    public abstract <D> Loader<D> getLoader(int id);

    /**
     * Mark all Loaders associated with this LoaderManager for redelivery of their current
     * data (if any), waiting for the next time the Loader is started if it is currently stopped.
     * In cases where no data has yet been delivered, this is effectively a no-op. In cases where
     * data has already been delivered via {@link LoaderCallbacks#onLoadFinished(Loader, Object)},
     * this will ensure that {@link LoaderCallbacks#onLoadFinished(Loader, Object)} is called again
     * with the same data.
     * <p>
     * Call this only if you are implementing a {@link LifecycleOwner} where the views/elements that
     * developers are likely to use in {@link LoaderCallbacks#onLoadFinished(Loader, Object)} can be
     * created and destroyed multiple times without the {@link LifecycleOwner} itself being
     * destroyed. Call this when the views/elements are being destroyed to ensure that the data
     * is redelivered upon recreation.
     */
    public abstract void markForRedelivery();

    /**
     * Print the LoaderManager's state into the given stream.
     *
     * @param prefix Text to print at the front of each line.
     * @param fd The raw file descriptor that the dump is being sent to.
     * @param writer A PrintWriter to which the dump is to be set.
     * @param args Additional arguments to the dump request.
     * @deprecated Use {@link #enableDebugLogging(boolean)} to understand the series of operations
     * performed by LoaderManager.
     */
    @Deprecated
    public abstract void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args);

    /**
     * Control whether the framework's internal loader manager debugging
     * logs are turned on.  If enabled, you will see output in logcat as
     * the framework performs loader operations.
     */
    public static void enableDebugLogging(boolean enabled) {
        LoaderManagerImpl.DEBUG = enabled;
    }

    /**
     * Returns true if any loaders managed are currently running and have not
     * returned data to the application yet.
     */
    public boolean hasRunningLoaders() { return false; }
}

 

LoadManager.LoaderCallbacks

LoadManager.LoaderCallbacks::onCreateLoader

 

LoadManager.LoaderCallbacks::onLoadFinished

 

 

LoadManager.LoaderCallbacks::onLoaderReset

 

 

LoaderManager::getInstance

 

LoaderManager::initLoader

 

 

LoaderManager::restartLoader

 

 

 

 

LoaderManager::destroytLoader

 

 

 

LoaderManager::markForRedelivery

 

 

 

2、LoaderManagerImpl

/*
 * Copyright 2018 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.loader.app;

import android.os.Bundle;
import android.os.Looper;
import android.util.Log;

import androidx.annotation.MainThread;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.collection.SparseArrayCompat;
import androidx.core.util.DebugUtils;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelStore;
import androidx.loader.content.Loader;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.lang.reflect.Modifier;

class LoaderManagerImpl extends LoaderManager {
    static final String TAG = "LoaderManager";
    static boolean DEBUG = false;

    /**
     * Class which manages the state of a {@link Loader} and its associated
     * {@link LoaderCallbacks}
     *
     * @param <D> Type of data the Loader handles
     */
    public static class LoaderInfo<D> extends MutableLiveData<D>
            implements Loader.OnLoadCompleteListener<D> {

        private final int mId;
        private final @Nullable Bundle mArgs;
        private final @NonNull Loader<D> mLoader;
        private LifecycleOwner mLifecycleOwner;
        private LoaderObserver<D> mObserver;
        private Loader<D> mPriorLoader;

        LoaderInfo(int id, @Nullable Bundle args, @NonNull Loader<D> loader,
                @Nullable Loader<D> priorLoader) {
            mId = id;
            mArgs = args;
            mLoader = loader;
            mPriorLoader = priorLoader;
            mLoader.registerListener(id, this);
        }

        @NonNull
        Loader<D> getLoader() {
            return mLoader;
        }

        @Override
        protected void onActive() {
            if (DEBUG) Log.v(TAG, "  Starting: " + LoaderInfo.this);
            mLoader.startLoading();
        }

        @Override
        protected void onInactive() {
            if (DEBUG) Log.v(TAG, "  Stopping: " + LoaderInfo.this);
            mLoader.stopLoading();
        }

        /**
         * Set the {@link LoaderCallbacks} to associate with this {@link Loader}. This
         * removes any existing {@link LoaderCallbacks}.
         *
         * @param owner The lifecycle that should be used to start and stop the {@link Loader}
         * @param callback The new {@link LoaderCallbacks} to use
         * @return The {@link Loader} associated with this LoaderInfo
         */
        @MainThread
        @NonNull
        Loader<D> setCallback(@NonNull LifecycleOwner owner,
                @NonNull LoaderCallbacks<D> callback) {
            LoaderObserver<D> observer = new LoaderObserver<>(mLoader, callback);
            // Add the new observer
            observe(owner, observer);
            // Loaders only support one observer at a time, so remove the current observer, if any
            if (mObserver != null) {
                removeObserver(mObserver);
            }
            mLifecycleOwner = owner;
            mObserver = observer;
            return mLoader;
        }

        void markForRedelivery() {
            LifecycleOwner lifecycleOwner = mLifecycleOwner;
            LoaderObserver<D> observer = mObserver;
            if (lifecycleOwner != null && observer != null) {
                // Removing and re-adding the observer ensures that the
                // observer is called again, even if they had already
                // received the current data
                // Use super.removeObserver to avoid nulling out mLifecycleOwner & mObserver
                super.removeObserver(observer);
                observe(lifecycleOwner, observer);
            }
        }

        boolean isCallbackWaitingForData() {
            //noinspection SimplifiableIfStatement
            if (!hasActiveObservers()) {
                // No active observers means no one is waiting for data
                return false;
            }
            return mObserver != null && !mObserver.hasDeliveredData();
        }

        @Override
        public void removeObserver(@NonNull Observer<? super D> observer) {
            super.removeObserver(observer);
            // Clear out our references when the observer is removed to avoid leaking
            mLifecycleOwner = null;
            mObserver = null;
        }

        /**
         * Destroys this LoaderInfo, its underlying {@link #getLoader() Loader}, and removes any
         * existing {@link androidx.loader.app.LoaderManager.LoaderCallbacks}.
         *
         * @param reset Whether the LoaderCallbacks and Loader should be reset.
         * @return When reset is false, returns any Loader that still needs to be reset
         */
        @MainThread
        Loader<D> destroy(boolean reset) {
            if (DEBUG) Log.v(TAG, "  Destroying: " + this);
            // First tell the Loader that we don't need it anymore
            mLoader.cancelLoad();
            mLoader.abandon();
            // Then clean up the LoaderObserver
            LoaderObserver<D> observer = mObserver;
            if (observer != null) {
                removeObserver(observer);
                if (reset) {
                    observer.reset();
                }
            }
            // Finally, clean up the Loader
            mLoader.unregisterListener(this);
            if ((observer != null && !observer.hasDeliveredData()) || reset) {
                mLoader.reset();
                return mPriorLoader;
            }
            return mLoader;
        }

        @Override
        public void onLoadComplete(@NonNull Loader<D> loader, @Nullable D data) {
            if (DEBUG) Log.v(TAG, "onLoadComplete: " + this);
            if (Looper.myLooper() == Looper.getMainLooper()) {
                setValue(data);
            } else {
                // The Loader#deliverResult method that calls this should
                // only be called on the main thread, so this should never
                // happen, but we don't want to lose the data
                if (DEBUG) {
                    Log.w(TAG, "onLoadComplete was incorrectly called on a "
                            + "background thread");
                }
                postValue(data);
            }
        }

        @Override
        public void setValue(D value) {
            super.setValue(value);
            // Now that the new data has arrived, we can reset any prior Loader
            if (mPriorLoader != null) {
                mPriorLoader.reset();
                mPriorLoader = null;
            }
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder(64);
            sb.append("LoaderInfo{");
            sb.append(Integer.toHexString(System.identityHashCode(this)));
            sb.append(" #");
            sb.append(mId);
            sb.append(" : ");
            DebugUtils.buildShortClassTag(mLoader, sb);
            sb.append("}}");
            return sb.toString();
        }

        @SuppressWarnings("deprecation")
        public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
            writer.print(prefix); writer.print("mId="); writer.print(mId);
            writer.print(" mArgs="); writer.println(mArgs);
            writer.print(prefix); writer.print("mLoader="); writer.println(mLoader);
            mLoader.dump(prefix + "  ", fd, writer, args);
            if (mObserver != null) {
                writer.print(prefix); writer.print("mCallbacks="); writer.println(mObserver);
                mObserver.dump(prefix + "  ", writer);
            }
            writer.print(prefix); writer.print("mData="); writer.println(
                    getLoader().dataToString(getValue()));
            writer.print(prefix); writer.print("mStarted="); writer.println(
                    hasActiveObservers());
        }
    }

    /**
     * Encapsulates the {@link LoaderCallbacks} as a {@link Observer}.
     *
     * @param <D> Type of data the LoaderCallbacks handles
     */
    static class LoaderObserver<D> implements Observer<D> {

        private final @NonNull Loader<D> mLoader;
        private final @NonNull LoaderCallbacks<D> mCallback;

        private boolean mDeliveredData = false;

        LoaderObserver(@NonNull Loader<D> loader, @NonNull LoaderCallbacks<D> callback) {
            mLoader = loader;
            mCallback = callback;
        }

        @Override
        public void onChanged(@Nullable D data) {
            if (DEBUG) {
                Log.v(TAG, "  onLoadFinished in " + mLoader + ": "
                        + mLoader.dataToString(data));
            }
            mCallback.onLoadFinished(mLoader, data);
            mDeliveredData = true;
        }

        boolean hasDeliveredData() {
            return mDeliveredData;
        }

        @MainThread
        void reset() {
            if (mDeliveredData) {
                if (DEBUG) Log.v(TAG, "  Resetting: " + mLoader);
                mCallback.onLoaderReset(mLoader);
            }
        }

        @Override
        public String toString() {
            return mCallback.toString();
        }

        public void dump(String prefix, PrintWriter writer) {
            writer.print(prefix); writer.print("mDeliveredData="); writer.println(
                    mDeliveredData);
        }
    }

    /**
     * ViewModel responsible for retaining {@link LoaderInfo} instances across configuration changes
     */
    static class LoaderViewModel extends ViewModel {
        private static final ViewModelProvider.Factory FACTORY = new ViewModelProvider.Factory() {
            @NonNull
            @Override
            @SuppressWarnings("unchecked")
            public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
                return (T) new LoaderViewModel();
            }
        };

        @NonNull
        static LoaderViewModel getInstance(ViewModelStore viewModelStore) {
            return new ViewModelProvider(viewModelStore, FACTORY).get(LoaderViewModel.class);
        }

        private SparseArrayCompat<LoaderInfo> mLoaders = new SparseArrayCompat<>();
        private boolean mCreatingLoader = false;

        void startCreatingLoader() {
            mCreatingLoader = true;
        }

        boolean isCreatingLoader() {
            return mCreatingLoader;
        }

        void finishCreatingLoader() {
            mCreatingLoader = false;
        }

        void putLoader(int id, @NonNull LoaderInfo info) {
            mLoaders.put(id, info);
        }

        @SuppressWarnings("unchecked")
        <D> LoaderInfo<D> getLoader(int id) {
            return mLoaders.get(id);
        }

        void removeLoader(int id) {
            mLoaders.remove(id);
        }

        boolean hasRunningLoaders() {
            int size = mLoaders.size();
            for (int index = 0; index < size; index++) {
                LoaderInfo info = mLoaders.valueAt(index);
                if (info.isCallbackWaitingForData()) {
                    return true;
                }
            }
            return false;
        }

        void markForRedelivery() {
            int size = mLoaders.size();
            for (int index = 0; index < size; index++) {
                LoaderInfo info = mLoaders.valueAt(index);
                info.markForRedelivery();
            }
        }

        @Override
        protected void onCleared() {
            super.onCleared();
            int size = mLoaders.size();
            for (int index = 0; index < size; index++) {
                LoaderInfo info = mLoaders.valueAt(index);
                info.destroy(true);
            }
            mLoaders.clear();
        }

        public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
            if (mLoaders.size() > 0) {
                writer.print(prefix); writer.println("Loaders:");
                String innerPrefix = prefix + "    ";
                for (int i = 0; i < mLoaders.size(); i++) {
                    LoaderInfo info = mLoaders.valueAt(i);
                    writer.print(prefix); writer.print("  #"); writer.print(mLoaders.keyAt(i));
                    writer.print(": "); writer.println(info.toString());
                    info.dump(innerPrefix, fd, writer, args);
                }
            }
        }
    }

    private final @NonNull LifecycleOwner mLifecycleOwner;
    private final @NonNull LoaderViewModel mLoaderViewModel;

    LoaderManagerImpl(@NonNull LifecycleOwner lifecycleOwner,
            @NonNull ViewModelStore viewModelStore) {
        mLifecycleOwner = lifecycleOwner;
        mLoaderViewModel = LoaderViewModel.getInstance(viewModelStore);
    }

    @MainThread
    @NonNull
    private <D> Loader<D> createAndInstallLoader(int id, @Nullable Bundle args,
            @NonNull LoaderCallbacks<D> callback, @Nullable Loader<D> priorLoader) {
        LoaderInfo<D> info;
        try {
            mLoaderViewModel.startCreatingLoader();
            Loader<D> loader = callback.onCreateLoader(id, args);
            if (loader == null) {
                throw new IllegalArgumentException("Object returned from onCreateLoader "
                        + "must not be null");
            }
            if (loader.getClass().isMemberClass()
                    && !Modifier.isStatic(loader.getClass().getModifiers())) {
                throw new IllegalArgumentException("Object returned from onCreateLoader "
                        + "must not be a non-static inner member class: "
                        + loader);
            }
            info = new LoaderInfo<>(id, args, loader, priorLoader);
            if (DEBUG) Log.v(TAG, "  Created new loader " + info);
            mLoaderViewModel.putLoader(id, info);
        } finally {
            mLoaderViewModel.finishCreatingLoader();
        }
        return info.setCallback(mLifecycleOwner, callback);
    }

    @MainThread
    @NonNull
    @Override
    public <D> Loader<D> initLoader(int id, @Nullable Bundle args,
            @NonNull LoaderCallbacks<D> callback) {
        if (mLoaderViewModel.isCreatingLoader()) {
            throw new IllegalStateException("Called while creating a loader");
        }
        if (Looper.getMainLooper() != Looper.myLooper()) {
            throw new IllegalStateException("initLoader must be called on the main thread");
        }

        LoaderInfo<D> info = mLoaderViewModel.getLoader(id);

        if (DEBUG) Log.v(TAG, "initLoader in " + this + ": args=" + args);

        if (info == null) {
            // Loader doesn't already exist; create.
            return createAndInstallLoader(id, args, callback, null);
        } else {
            if (DEBUG) Log.v(TAG, "  Re-using existing loader " + info);
            return info.setCallback(mLifecycleOwner, callback);
        }
    }

    @MainThread
    @NonNull
    @Override
    public <D> Loader<D> restartLoader(int id, @Nullable Bundle args,
            @NonNull LoaderCallbacks<D> callback) {
        if (mLoaderViewModel.isCreatingLoader()) {
            throw new IllegalStateException("Called while creating a loader");
        }
        if (Looper.getMainLooper() != Looper.myLooper()) {
            throw new IllegalStateException("restartLoader must be called on the main thread");
        }

        if (DEBUG) Log.v(TAG, "restartLoader in " + this + ": args=" + args);
        LoaderInfo<D> info = mLoaderViewModel.getLoader(id);
        Loader<D> priorLoader = null;
        if (info != null) {
            priorLoader = info.destroy(false);
        }
        // And create a new Loader
        return createAndInstallLoader(id, args, callback, priorLoader);
    }

    @MainThread
    @Override
    public void destroyLoader(int id) {
        if (mLoaderViewModel.isCreatingLoader()) {
            throw new IllegalStateException("Called while creating a loader");
        }
        if (Looper.getMainLooper() != Looper.myLooper()) {
            throw new IllegalStateException("destroyLoader must be called on the main thread");
        }

        if (DEBUG) Log.v(TAG, "destroyLoader in " + this + " of " + id);
        LoaderInfo info = mLoaderViewModel.getLoader(id);
        if (info != null) {
            info.destroy(true);
            mLoaderViewModel.removeLoader(id);
        }
    }

    @Nullable
    @Override
    public <D> Loader<D> getLoader(int id) {
        if (mLoaderViewModel.isCreatingLoader()) {
            throw new IllegalStateException("Called while creating a loader");
        }

        LoaderInfo<D> info = mLoaderViewModel.getLoader(id);
        return info != null ? info.getLoader() : null;
    }

    @Override
    public void markForRedelivery() {
        mLoaderViewModel.markForRedelivery();
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(128);
        sb.append("LoaderManager{");
        sb.append(Integer.toHexString(System.identityHashCode(this)));
        sb.append(" in ");
        DebugUtils.buildShortClassTag(mLifecycleOwner, sb);
        sb.append("}}");
        return sb.toString();
    }

    @Deprecated
    @Override
    public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
        mLoaderViewModel.dump(prefix, fd, writer, args);
    }

    @Override
    public boolean hasRunningLoaders() {
        return mLoaderViewModel.hasRunningLoaders();
    }
}

 LoadInfo就是LiveData
LoaderViewModel就是ViewModel

LoaderObserver就是Observer