我只想使用设备中缓存的OSM地图作为google maps api v2的磁贴提供程序。我已阅读this useful question，但我不知道如何缓存切片。
我有我国家/地区的osm文件，但是如何获得包含所有png文件的有组织文件夹？
如果缓存设备中的所有png文件太重，android中是否有任何库可以直接从osm.pbf文件中获取文件？
请注意，我想继续使用googles map api而不是替换。
答案 0 :(得分：2)
我不知道pbf库（如果能够，你应该检查OSMDroid）。 无论如何，我成功地在运行时自己缓存来自openstreetmap的png。这意味着我只缓存了显示的磁贴而不是所有区域（我做了强力下载，但我不建议这样做）。 我将留下“缓存”活动磁贴的代码，如果您想要与应用程序一起提供png，然后阅读它们，您可以尝试将png放在第一级作为缩放级别的文件夹结构中（ Z），然后为行/纬度（y）和列/经度（x）放置另外两个级别，这里放置文件，如果文件具有以下三个值，则更好：Z_Y_X.png
您必须编辑“getTile”方法，以检查上面创建的文件夹结构中的PNG文件。
这是我的“实时缓存”代码
/*
* Copyright 2014 Google Inc. All rights reserved.
*
* 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.
*/
import com.jakewharton.disklrucache.DiskLruCache;
/**
* Wrapper that provides a disk-based LRU cache for a TileProvider.
*
* @see DiskLruCache
*/
public class CachedTileProvider implements TileProvider {
private static final String TAG = CachedTileProvider.class.getSimpleName();
private static final String KEY_FORMAT = "%3$d_%2$d_%1$d_%4$s";
// Index for cache entry streams
private static final int INDEX_DATA = 0;
private static final int INDEX_HEIGHT = 1;
private static final int INDEX_WIDTH = 2;
//TEST
private static final double[] TILES_ORIGIN = {-20037508.34789244, 20037508.34789244};//TODO Duplicate from WMS PROVIDER, put as utils
// Size of square world map in meters, using WebMerc projection.
private static final double MAP_SIZE = 20037508.34789244 * 2;//TODO Duplicate from WMS PROVIDER, put as utils
private static final double ORIGIN_SHIFT = Math.PI * 6378137d;
//TEST
private final String mKeyTag;
private final TileProvider mTileProvider;
//private final DiskLruCache mCache;
private DiskLruCache mCache;
private Set<String> cachedStringsWMS = null;
Context cont = null;
/**
* TileProvider that wraps another TileProvider and caches all Tiles in a DiskLruCache.
* <p/>
* <p>A {@link DiskLruCache} can be reused across multiple instances.
* The keyTag is used to annotate entries for this TileProvider, it is recommended to use a unique
* String for each instance to prevent collisions.
* <p/>
* <p>NOTE: The supplied {@link DiskLruCache} requires space for
* 3 entries per cached object.
*
* @param keyTag identifier used to identify tiles for this CachedTileProvider instance
* @param tileProvider tiles from this TileProvider will be cached.
* @param cache the cache used to store tiles
*/
public CachedTileProvider(String keyTag, TileProvider tileProvider, DiskLruCache cache, Context context) {
mKeyTag = keyTag;
mTileProvider = tileProvider;
mCache = cache;
cont = context;
}
public void setNewDiskCache(DiskLruCache cache) {
mCache = cache;
}
/**
* Load a tile.
* If cached, the data for the tile is read from the underlying cache, otherwise the tile is
* generated by the {@link com.google.android.gms.maps.model.TileProvider} and added to the
* cache.
*
* @param x
* @param y
* @param zoom
* @return
*/
@Override
public Tile getTile(int x, int y, int zoom) {
final String key = CachedTileProvider.generateKey(x, y, zoom, mKeyTag);
Tile tile = getCachedTile(key);
if (tile == null) {
// tile not cached, load from provider and then cache
tile = mTileProvider.getTile(x, y, zoom);
if (null != tile && cacheTile(key, tile)) {
if (BuildConfig.DEBUG) Log.d(TAG, "Added tile to cache " + key);
}
}
return tile;
}
/**
* Load a tile from cache.
* Returns null if there is no corresponding cache entry or it could not be loaded.
*
* @param key
* @return
*/
private Tile getCachedTile(String key) {
try {
DiskLruCache.Snapshot snapshot = mCache.get(key);
if (snapshot == null) {
// tile is not in cache
return null;
}
final byte[] data = readStreamAsByteArray(snapshot.getInputStream(INDEX_DATA));
final int height = readStreamAsInt(snapshot.getInputStream(INDEX_HEIGHT));
final int width = readStreamAsInt(snapshot.getInputStream(INDEX_WIDTH));
if (data != null) {
if (BuildConfig.DEBUG)Log.d(TAG, "Cache hit for tile " + key);
return new Tile(width, height, data);
}
} catch (IOException e) {
// ignore error
e.printStackTrace();
} catch (IllegalStateException ise) {
Log.e(TAG, "IllegalStateException thrown, maybe cache is closed: " + ise.getMessage(), ise);
}
return null;
}
private boolean cacheTile(String key, Tile tile) {
try {
DiskLruCache.Editor editor = mCache.edit(key);
if (editor == null) {
// editor is not available
return false;
}
writeByteArrayToStream(tile.data, editor.newOutputStream(INDEX_DATA));
writeIntToStream(tile.height, editor.newOutputStream(INDEX_HEIGHT));
writeIntToStream(tile.width, editor.newOutputStream(INDEX_WIDTH));
editor.commit();
return true;
} catch (IOException e) {
// Tile could not be cached
e.printStackTrace();
} catch (IllegalStateException ise) {
Log.e(TAG, "IllegalStateException thrown, maybe cache is closed: " + ise.getMessage(), ise);
}
return false;
}
private static String generateKey(int x, int y, int zoom, String tag) {
return String.format(KEY_FORMAT, x, y, zoom, tag);
}
private static void writeByteArrayToStream(byte[] data, OutputStream stream) throws IOException {
try {
stream.write(data);
} finally {
stream.close();
}
}
private static void writeIntToStream(int data, OutputStream stream) throws IOException {
DataOutputStream dos = new DataOutputStream(stream);
try {
dos.writeInt(data);
} finally {
try {
dos.close();
} finally {
stream.close();
}
}
}
private static byte[] readStreamAsByteArray(InputStream inputStream) throws IOException {
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int read = 0;
byte[] data = new byte[1024];
try {
while ((read = inputStream.read(data, 0, data.length)) != -1) {
buffer.write(data, 0, read);
}
} finally {
inputStream.close();
}
return buffer.toByteArray();
}
private static int readStreamAsInt(InputStream inputStream) throws IOException {
DataInputStream buffer = new DataInputStream(inputStream);
try {
return buffer.readInt();
} finally {
inputStream.close();
}
}
}
然后通过包装Tile提供程序创建一个实例：
CachedTileProvider cachedTileProvider = new CachedTileProvider("osm", TileProviderFactory.getOSMBackGroundTileProvider(layerInfo.get(i)), mContext);
，其中
public static TileProvider getOSMBackGroundTileProvider() {
TileProvider mOSMTileProvider = new UrlTileProvider(256, 256) {
@Override
public URL getTileUrl(int x, int y, int z) {
try {
String f = "http://a.tile.openstreetmap.org/%d/%d/%d.png";
return new URL(String.format(f, z, x, y));
} catch (MalformedURLException e) {
return null;
}
}
};
return mOSMTileProvider;
}
您现在要从jakewharton探索并检查DiskLruCache库，但是有很多文档，如果需要，最好打开另一个问题。