Poznámka
Toto se nedoporučuje, protože by to stále pravděpodobně bylo značně neefektivní ve srovnání s ukládáním cesty k souboru obrázku.
Zřejmou odpovědí je rozdělit obrázek na části, které lze spravovat (kusy)
- (řekněme 256 000 kusů (14 takových kusů by pojme přibližně 3,5 Mb))
umožňující sestavení jednotlivých kusů v případě potřeby.
Jednoduchý příklad
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Tento příklad ilustruje ukládání, načítání, sestavení a zobrazení obrázku, který by byl příliš velký (přibližně 3,5 MB).
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Aby byl základní obrázek snadno dostupný, byl umístěn do složky aktiv a poté je aplikací zkopírován do dat aplikace (data/data/myimages/) (místo psaní dalšího kódu, řekněme použijte fotoaparát).
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jsou použity dvě tabulky
- tabulku s názvem imagemaster pro jednotlivá obrazová data, např. je to jméno a
- druhou tabulku s názvem imagechunk pro bloky, z nichž každý odkazuje na příslušný řádek v tabulce imagemaster.
Nápověda DatabaseHelper DBHelper.java :-
public class DBHelper extends SQLiteOpenHelper {
public static final String DBNAME = "mydb";
public static final int DBVERSION = 1;
public static final String TBL_IMAGEMASTER = "image_matser";
public static final String COL_IMAGEMASTER_ID = BaseColumns._ID;
public static final String COL_IMAGEMASTER_DESCRIPTION = "description";
public static final String COL_IMAGEMASTER_THUMBNAIL = "thumbnail";
public static final String TBL_IMAGECHUNK = "imagechunk";
public static final String COL_IMAGECHUNK_ID = BaseColumns._ID;
public static final String COL_IMAGECHUNK_OWNER = "owner";
public static final String COL_IMAGECHUNK_CHUNK = "chunk";
public static final String COL_IMAGECHUNK_CHUNKORDER = "chunkorder";
public static final String COL_IMAGECHUNK_CHUNKSIZE = "chunksize";
public static final int MAXIMUM_CHUNK_SIZE = 256 * 1024; // 256k chunks
// Some codes for when/if things go wrong
public static final long NOSUCHFILE = -2;
public static final long INPUT_ASSIGN_IO_ERROR = -3;
public static final long INPUT_READ_IO_ERROR = -4;
public static final long CHUNKCOUNTMISMATCH = -5;
SQLiteDatabase mDB;
public DBHelper(Context context) {
super(context, DBNAME, null, DBVERSION);
mDB = this.getWritableDatabase(); //Open the database
}
@Override
public void onCreate(SQLiteDatabase db) {
// The imagemaster table
String mImageMasterCrtSQL = "CREATE TABLE IF NOT EXISTS " + TBL_IMAGEMASTER + "(" +
COL_IMAGEMASTER_ID + " INTEGER PRIMARY KEY, " +
COL_IMAGEMASTER_DESCRIPTION + " TEXT UNIQUE, " +
COL_IMAGEMASTER_THUMBNAIL + " BLOB DEFAULT x'00' " +
")";
db.execSQL(mImageMasterCrtSQL);
// The imagechunk table
String mImageChunkCrtSQL = "CREATE TABLE IF NOT EXISTS " + TBL_IMAGECHUNK + "(" +
COL_IMAGECHUNK_ID + " INTEGER PRIMARY KEY, " +
COL_IMAGECHUNK_OWNER + " INTEGER REFERENCES " + TBL_IMAGEMASTER + "(" +
COL_IMAGEMASTER_ID +
")," +
COL_IMAGECHUNK_CHUNKORDER + " INTEGER, " +
COL_IMAGECHUNK_CHUNKSIZE + " INTEGER, " +
COL_IMAGECHUNK_CHUNK + " BLOB DEFAULT x'00'" +
")";
db.execSQL(mImageChunkCrtSQL);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// Need to turn on FOREIGN KEY support
@Override
public void onConfigure(SQLiteDatabase db) {
super.onConfigure(db);
db.setForeignKeyConstraintsEnabled(true);
}
// Add an imagemaster row (private as imagemaster row and imagechunk rows are to be added together)
private long addImageMaster(String description, byte[] thumbnail) {
ContentValues cv = new ContentValues();
cv.put(COL_IMAGEMASTER_DESCRIPTION,description);
if (thumbnail.length > 0) {
cv.put(COL_IMAGEMASTER_THUMBNAIL,thumbnail);
}
return mDB.insert(TBL_IMAGEMASTER,null,cv);
}
// Add an imagechunk row (private as imagemaster and imagechucks will be added togther)
private long addImageChunk(long owningImage, long order, byte[] image) {
ContentValues cv = new ContentValues();
cv.put(COL_IMAGECHUNK_OWNER,owningImage);
cv.put(COL_IMAGECHUNK_CHUNKORDER,order);
cv.put(COL_IMAGECHUNK_CHUNKSIZE,image.length);
cv.put(COL_IMAGECHUNK_CHUNK,image);
return mDB.insert(TBL_IMAGECHUNK,null,cv);
}
// Add imagemaster and all imagechunk rows from a File
public long storeImageFromFile(String description, File image, byte[] thumbnail, boolean printstacktrace) {
long rv = NOSUCHFILE;
long master_id;
if (!image.exists()) {
return rv;
}
//Get image info from file
long chunkcount = (image.length() / (long) MAXIMUM_CHUNK_SIZE);
if ((image.length() - (chunkcount * (long) MAXIMUM_CHUNK_SIZE)) > 0) {
chunkcount++;
}
// Add the image master row
rv = addImageMaster(description, thumbnail);
if (rv < 1) {
return rv;
}
master_id = rv;
// Prepare to save chunks
byte[] buffer = new byte[MAXIMUM_CHUCK_SIZE];
int currentchunk = 0;
int readlength = 0;
rv = INPUT_ASSIGN_IO_ERROR;
long chunksavedcount = 0;
try {
InputStream is = new FileInputStream(image);
rv = INPUT_READ_IO_ERROR;
while ((readlength = is.read(buffer)) > 0) {
if (readlength == MAXIMUM_CHUNK_SIZE) {
if (addImageChunk(master_id, currentchunk++, buffer) > 0) {
chunksavedcount++;
}
} else {
byte[] lastbuffer = new byte[readlength];
for (int i = 0; i < readlength; i++) {
lastbuffer[i] = buffer[i];
}
if (addImageChunk(master_id, currentchunk, lastbuffer) > 0) {
chunksavedcount++;
}
}
}
is.close();
} catch (IOException ioe) {
if (printstacktrace) {
ioe.printStackTrace();
}
return rv;
}
if (chunksavedcount != chunkcount) {
rv = CHUNKCOUNTMISMATCH;
}
return rv;
}
//Get the image as a byte array (could easily return a BitMap) according to the image description
public byte[] getAllChunksAsByteArray(String imageDescription) {
String column_chucksize_sum = "chuck_size_sum";
long master_id = -1;
int imagesize = 0;
//Stage 1 get the image master id according to the description
String[] columns = new String[]{COL_IMAGEMASTER_ID};
String whereclause = COL_IMAGEMASTER_DESCRIPTION + "=?";
String[] whereargs = new String[]{imageDescription};
Cursor csr = mDB.query(TBL_IMAGEMASTER,columns,whereclause,whereargs,null,null,null,null);
if (csr.moveToFirst()) {
master_id = csr.getLong(csr.getColumnIndex(COL_IMAGEMASTER_ID));
}
//If no such image then return empty byte array
if (master_id < 1) {
csr.close();
return new byte[0];
}
// Stage 2 get the total size of the image
columns = new String[]{"sum(" + COL_IMAGECHUNK_CHUNKSIZE + ") AS " + column_chucksize_sum};
whereclause = COL_IMAGECHUNK_OWNER + "=?";
whereargs = new String[]{String.valueOf(master_id)};
csr = mDB.query(TBL_IMAGECHUNK,columns,whereclause,whereargs,null,null,COL_IMAGECHUNK_CHUNKORDER + " ASC");
if (csr.moveToFirst()) {
imagesize = csr.getInt(csr.getColumnIndex(column_chucksize_sum));
}
//If no chunks or all chunks are empty return empty byte array
if (imagesize < 1) {
csr.close();
return new byte[0];
}
//Stage 3 combine all the chunks into a single byte array
columns = new String[]{COL_IMAGECHUNK_CHUNK, COL_IMAGECHUNK_CHUNKSIZE};
csr = mDB.query(TBL_IMAGECHUNK,columns,whereclause,whereargs,null,null,COL_IMAGECHUNK_CHUNKORDER + " ASC");
if (csr.getCount() < 1) {
csr.close();
return new byte[0];
}
int rv_offset = 0;
byte[] rv = new byte[imagesize];
while (csr.moveToNext()) {
int currentsize = csr.getInt(csr.getColumnIndex(COL_IMAGECHUNK_CHUNKSIZE));
byte[] thischunk = csr.getBlob(csr.getColumnIndex(COL_IMAGECHUNK_CHUNK));
for (int i = 0; i < thischunk.length; i++) {
rv[rv_offset + i] = thischunk[i];
}
rv_offset = rv_offset + currentsize;
}
csr.close();
return rv;
}
}
The Activity MainActivity.java
public class MainActivity extends AppCompatActivity {
DBHelper mDBHlpr; //The database helper
ImageView mMyImageView; //For displaying the image (initially nothing shown)
Button mTestIt; //Button that will retrieve the image from the DB and display it
String mSaveDirectory = "myimages"; //The directory in which to save the image file
byte[] extracted_image; //For the retrieved image
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mMyImageView = this.findViewById(R.id.myimageview);
mTestIt = this.findViewById(R.id.testit);
mTestIt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showimage(extracted_image); //<<<<<<<<<< extract the image and display it.
}
});
mDBHlpr = new DBHelper(this); //<<<<<<<<<< instantiate the Database Helper
String testfilename = "20141107 1924 SCC Bedroom.JPG"; //The file to get from the assets folder
String testdescription = "MyTestImage"; //The description to give the image
//1. copy the file from the assets folder e.g. akin to taking photo from camera
File testfile = new File(saveAssetAsFile(testfilename));
//2. Add the image and the chucks to the DB
mDBHlpr.storeImageFromFile(testdescription,testfile,new byte[]{0,1,2,3,4,5,6},true);
//3. Extract the rows and write them to the log
Cursor csr = mDBHlpr.getWritableDatabase().query(DBHelper.TBL_IMAGEMASTER,null,null,null,null,null,null);
DatabaseUtils.dumpCursor(csr);
csr = mDBHlpr.getWritableDatabase().query(DBHelper.TBL_IMAGECHUNK,null,null,null,null,null,null);
DatabaseUtils.dumpCursor(csr);
csr.close();
//4. extract the byte array for the image display the length of the byte array
extracted_image = mDBHlpr.getAllChunksAsByteArray(testdescription);
Log.d("EXTRACTED","The extracted image size is " + String.valueOf(extracted_image.length));
}
//Copy the asset to a file
private String saveAssetAsFile(String asset) {
//For ease use data/data/<package_name>/myimages to save the image as a file
//Note a bit of a cheat as getDatabasePath will return data/data/<package_name>/databases/xxx (or equivalent)
//GetDatabasepath available for all Android versions
String filepath = this.getDatabasePath("xxx").getParentFile().getParent() + File.separator + mSaveDirectory + File.separator + asset;
File savelocation = new File(filepath);
//If the file exists then no need to copy again so return
if (savelocation.exists()) return savelocation.getPath();
//Create the myimages directory if needed (will be required first run)
if (!savelocation.getParentFile().exists()) {
savelocation.getParentFile().mkdirs();
}
byte[] buffer = new byte[DBHelper.MAXIMUM_CHUNK_SIZE]; //Use 256k buffer as size is defined
int buffer_length;
try {
InputStream is = this.getAssets().open(asset);
FileOutputStream os = new FileOutputStream(savelocation);
while ((buffer_length = is.read(buffer)) > 0) {
os.write(buffer,0,buffer_length);
}
os.flush();
os.close();
is.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
return savelocation.getPath();
}
private void showimage(byte[] imagetoshow) {
Bitmap bmp = BitmapFactory.decodeByteArray(imagetoshow, 0, imagetoshow.length);
mMyImageView.setImageBitmap(bmp);
}
}
Výsledek
Když je aplikace spuštěna (bez obrázku):-
Po kliknutí na tlačítko :-
Obrázek je extrahován z DB
Záznam :-
........
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: 13 {
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: _id=14
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: owner=1
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: chunkorder=13
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: chunksize=97210
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: chunk=<unprintable>
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: }
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: <<<<<
03-24 16:44:36.423 22859-22859/aaa.so55276671hiddenimages W/CursorWindow: Window is full: requested allocation 262144 bytes, free space 261532 bytes, window size 2097152 bytes
03-24 16:44:36.441 22859-22859/aaa.so55276671hiddenimages W/CursorWindow: Window is full: requested allocation 262144 bytes, free space 261532 bytes, window size 2097152 bytes
03-24 16:44:36.453 22859-22859/aaa.so55276671hiddenimages D/EXTRACTED: The extracted image size is 3505082
........... click the button
03-24 16:50:09.565 22859-22859/aaa.so55276671hiddenimages D/BEFOREEXTRACT: Button clicked so extracting image.
03-24 16:50:09.583 22859-22872/aaa.so55276671hiddenimages I/art: Background sticky concurrent mark sweep GC freed 1882(116KB) AllocSpace objects, 7(1631KB) LOS objects, 0% free, 65MB/65MB, paused 6.779ms total 17.678ms
03-24 16:50:09.765 22859-22859/aaa.so55276671hiddenimages D/AFTEREXTRACT: Finished extracting the image.
- Všimněte si, že úplné zprávy CursorWindow nejsou selhání, spíše jen říkají, že byl učiněn pokus o přidání řádku, ale byl plný.
- UPOZORNĚNÍ Jak je vidět, 5 takových obrázků by extrahování a zobrazení trvalo 1 sekundu