Question

我像这样将图像字节保存到数据库。

 byte[] imagebyte = getBytes(bitmap);
 boolean isuploaded = myDb.insertData("all_receipts",imagebyte);




 public byte[] getBytes(Bitmap bitmap) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG, 70, stream);

    return stream.toByteArray();
}

然后我在我的数据库助手类中创建了一个检索方法来检索所有数据。

   public ArrayList<Model.Receipts> convertoArray(String tablename){
    ArrayList<Model.Receipts> receiptsArrayList = new ArrayList<>();
    Model.Receipts receipt;

    SQLiteDatabase database = this.getReadableDatabase();
    String selectQuery = "SELECT * FROM all_receipts";


    if(tablename.equalsIgnoreCase("all_receipts")){

        Cursor cursor = database.rawQuery(selectQuery, null);

        if (cursor.moveToFirst()) {
            do {
                int indexnumber = cursor.getInt(0);
                Bitmap image = getImage(cursor.getBlob(1));
                receipt = new Model.Receipts(image,indexnumber);

                receiptsArrayList.add(receipt);
            }
            while (cursor.moveToNext());
        }
    }
    return receiptsArrayList;

}

这与我从相机拍摄的图像缩略图一样正常。但是当我对完整尺寸的图像使用相同的方法时，它不起作用。我收到了错误

Unable to start activity 

   java.lang.IllegalStateException: Couldn't read row 0, col 0 from 
CursorWindow。在从中访问数据之前，请确保正确初始化Cursor。在

android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2255）at＆gt; android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2309）at？＆gt; android.app.ActivityThread.access $ 700（ActivityThread.java ：157）at＆gt; android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1289）

From which I know that it's because that the BLOB is too big in the database.

那么如何从数据库中调用所有图像？

Answer 1

将图像存储在数据库中并不是一个好主意。而是存储指向图像的URI ..并将图像存储在文件夹中。

如果您仍想将其作为字节存储在数据库中..您可以查看here。

但请记住，游标大小限制为1MB。

Answer 2

您应该将图像的路径存储到数据库中，并使用路径访问/显示图像。

示例

以下是一个示例，为方便起见，图像（image001.JPG到image010.JPG）存储在assets文件夹中。

该示例显示图像的列表（ListView），以及1个图像，然后单击列表中的项目将更改显示以通过存储的路径显示相应的图像。

首先，布局 activity_main.xml （注意包名称必须相应更改）： -

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="mjt.sqliteexamples.MainActivity">
    <ListView
        android:id="@+id/imagelist"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </ListView>
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <ImageView
                android:id="@+id/myimage"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:contentDescription="myImage"/>
        </LinearLayout>
    </ScrollView>
</LinearLayout>

DatabaseHelper ImgDBHelper.java

public class ImgDBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "myimagestore";
    public static final String TBLNAME = "images";
    public static final String ID_COL = "_id";
    public static final String DSCR_COL = "description";
    public static final String PATH_COL = "path"; //<<<<<<<<

    SQLiteDatabase db;

    ImgDBHelper(Context context) {
        super(context,DBNAME,null,1);
        db = this.getWritableDatabase();
    }
    @Override
    public void onCreate(SQLiteDatabase db) {    
        String crtsql = "CREATE TABLE IF NOT EXISTS " + TBLNAME + "(" +
                ID_COL + " INTEGER PRIMARY KEY, " +
                DSCR_COL + " TEXT," +
                PATH_COL + " TEXT" +
                ")";
        db.execSQL(crtsql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }

    public void addImageRow(String path, String description) {
        Cursor csr = db.query(TBLNAME,null,PATH_COL + "=?",new String[]{path},null,null,null);

        // DO NOT ADD DUPLICATE IMAGES (according to path)
        if (csr.getCount() > 0) {
            csr.close();
            return;
        }
        csr.close();

        ContentValues cv = new ContentValues();
        cv.put(DSCR_COL,description);
        cv.put(PATH_COL,path);

        db.insert(TBLNAME,null,cv);
    }

    public Cursor getAllImages() {
        return db.query(TBLNAME,null,null,null,null,null,null);
    }

    public String getImagePathFromID(long id) {
        String rv = "";
        Cursor csr = db.query(TBLNAME,
                null,
                "_id=?",
                new String[]{Long.toString(id)},
                null,null,null
        );
        if (csr.moveToFirst()) {
            rv = csr.getString(csr.getColumnIndex(PATH_COL));
        }
        csr.close();
        return rv;
    }

    public boolean areImagesLoaded() {
        Cursor csr = db.query(TBLNAME,null,null,null,null,null,null);
        boolean rv = (csr.getCount() > 0);
        csr.close();
        return rv;
    }
}

活动 MainActivity.java

public class MainActivity extends AppCompatActivity {

    Drawable d;                        // drawable for the image
    String imagepath = "image001.JPG"; // initial image
    ImgDBHelper imgdbhlpr;             // DB Helper
    ListView imagelist;                // ListView
    SimpleCursorAdapter sca;           // ListView's Cursor adapter
    Cursor images;                     // Cursor for the ListView
    ImageView iv;                      // The ImageView to display the image

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imagelist = (ListView) findViewById(R.id.imagelist);
        iv = (ImageView) findViewById(R.id.myimage);

        imgdbhlpr = new ImgDBHelper(this);

        // Load the table if there are no images
        if (!imgdbhlpr.areImagesLoaded()) {
            for (int i=1;i < 11;i++) {

                String path = "image" +
                        String.format("%03d",i) +
                                ".JPG"
                        ;
                imgdbhlpr.addImageRow(path,"Image " +
                String.format("%03d",i));
            }
        }

        // get a cursor with all of the rows
        images = imgdbhlpr.getAllImages();

        // prepare the listview's adapter
        sca = new SimpleCursorAdapter(this,
                android.R.layout.simple_list_item_1,
                images,
                new String[]{ImgDBHelper.DSCR_COL},
                new int[]{android.R.id.text1},
                0
        );

        // set the Listview's onItemClick listener so that clicking an
        // item displays the respective image
        imagelist.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                iv.setImageDrawable(d = getImageFromAssets(
                        imgdbhlpr.getImagePathFromID(l)
                ));
            }
        });
        imagelist.setAdapter(sca);

        // set the initial image (image001.JPG)
        d = getImageFromAssets(imagepath);
        iv.setImageDrawable(d);
    }


    // routine to create a drawable according to the supplied path
    private  Drawable getImageFromAssets(String imagepath) {
        Drawable drawable = null;
        AssetManager am = this.getAssets();
        InputStream is = null;
        try {
            is = am.open(imagepath);
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            drawable = Drawable.createFromStream(is,null);
        } finally {
            try {
                is.close();
                is = null;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return drawable;
    }
}

最初运行时： -

然后点击Listview（image004）后： -

如何从android中的数据库中检索大型BLOB？

2 个答案:

示例