android将图片转换存到数据库再从数据库读取转换成图片实现代码

首先，我们要把图片存入到数据库中，首先要创建一个数据库， 如下所示：

代码如下:

package com.android.test;

import java.io.ByteArrayOutputStream;

import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.provider.BaseColumns;

public class PictureDatabase extends SQLiteOpenHelper {

//数据库的字段
    public static class PictureColumns implements BaseColumns {
        public static final String PICTURE = "picture";
    }

private Context mContext;

//数据库名
    private static final String DATABASE_NAME = "picture.db";
    //数据库版本号
    private static final int DATABASE_Version = 1;
    //表名
    private static final String TABLE_NAME = "picture";

//创建数据库
    public PictureDatabase (Context context) {
        super(context, DATABASE_NAME, null, DATABASE_Version);
        this.mContext = context;
    }

//创建表并初始化表
    @Override
    public void onCreate (SQLiteDatabase db) {
        String sql = "Create table " + TABLE_NAME + "(" + BaseColumns._ID
        + " integer primary key autoincrement," + PictureColumns.PICTURE
        + " blob not null);";
        db.execSQL(sql);

//初始化
        initDataBase(db,mContext);
    }

//将转换后的图片存入到数据库中
    private void initDataBase (SQLiteDatabase db, Context context) {
        Drawable drawable = context.getResources().getDrawable(R.drawable.test_icon_resizer);
        ContentValues cv = new ContentValues();
        cv.put(PictureColumns.PICTURE, getPicture(drawable));
        db.insert(TABLE_NAME, null, cv);
    }

//将drawable转换成可以用来存储的byte[]类型
    private byte[] getPicture(Drawable drawable) {
        if(drawable == null) {
            return null;
        }
        BitmapDrawable bd = (BitmapDrawable) drawable;
        Bitmap bitmap = bd.getBitmap();
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        bitmap.compress(CompressFormat.PNG, 100, os);
        return os.toByteArray();
    }

//更新数据库
    @Override
    public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion) {
        String sql = " DROP TABLE IF EXISTS " + TABLE_NAME;
        db.execSQL(sql);
        onCreate(db);
    }
}

代码注释的比较详细.

这里重点要说的是初始化数据库的时候，将Drawable转变成byte[]的时候，先讲Drawable转换成Bitmap，然后将Bitmap存入字节数据输出流，从输出流里获取byte[]数组。

代码如下:

ByteArrayOutputStream os = new ByteArrayOutputStream();
bitmap.compress(CompressFormat.PNG, 100, os);
return os.toByteArray();

之后将字符数组存入到类型为blob的数据库中去。


代码如下:

ContentValues cv = new ContentValues();
cv.put(PictureColumns.PICTURE, getPicture(drawable));
db.insert(TABLE_NAME, null, cv);

之后在代码中从数据库中取出byte[]，然后转换成Drawable，设置图片即可。

代码如下：

代码如下:

package com.android.test;

import java.util.ArrayList;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.ImageView;

public class TestPicture extends Activity {

@Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ImageView iv = new ImageView(this);
        if(getDrawable().size() != 0) {
            iv.setImageDrawable(getDrawable().get(0));
        }
        setContentView(iv);
    }

private ArrayList<Drawable> getDrawable() {
        PictureDatabase pd = new PictureDatabase(this);
        SQLiteDatabase sd = pd.getWritableDatabase();

ArrayList<Drawable> drawables = new ArrayList<Drawable>();

//查询数据库
        Cursor c = sd.query("picture", null, null, null, null, null, null);

//遍历数据
        if(c != null && c.getCount() != 0) {
            while(c.moveToNext()) {
                //获取数据
                byte[] b = c.getBlob(c.getColumnIndexOrThrow(PictureDatabase.PictureColumns.PICTURE));
                //将获取的数据转换成drawable
                Bitmap bitmap = BitmapFactory.decodeByteArray(b, 0, b.length, null);
                BitmapDrawable bitmapDrawable = new BitmapDrawable(bitmap);
                Drawable drawable = bitmapDrawable;
                drawables.add(drawable);
            }
        }
        return drawables;
    }
}

重点注意如何将数据库中取出的byte[]转换成drawable：


代码如下:

Bitmap bitmap = BitmapFactory.decodeByteArray(b, 0, b.length, null);
BitmapDrawable bitmapDrawable = new BitmapDrawable(bitmap);
Drawable drawable = bitmapDrawable;

运行效果如下：