如何从SQLIte加载和检索文件？

时间：2014-08-25 16:33:00

标签： android sqlite

我尝试从数据库中检索数据，但是当我运行应用程序时，它显示错误“不幸的是，应用程序已停止”。

DataBaseHandler.java 

package com.example.sqliteimagedemo;

//package 
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DataBaseHandler extends SQLiteOpenHelper {

// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "imagedb";

// Contacts table name
private static final String TABLE_CONTACTS = "contacts";

// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_IMAGE = "image";

public DataBaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
+ KEY_IMAGE + " BLOB" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

// Create tables again
onCreate(db);
}

/**
* All CRUD(Create, Read, Update, Delete) Operations
*/

public// Adding new contact
void addContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();

ContentValues values = new ContentValues();
values.put(KEY_NAME, contact._name); // Contact Name
values.put(KEY_IMAGE, contact._image); // Contact Phone

// Inserting Row
db.insert(TABLE_CONTACTS, null, values);
db.close(); // Closing database connection
}

// Getting single contact
Contact getContact(int id) {
SQLiteDatabase db = this.getReadableDatabase();

Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
KEY_NAME, KEY_IMAGE }, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();

Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getBlob(1));

// return contact
return contact;

}

// Getting All Contacts
public List<Contact> getAllContacts() {
List<Contact> contactList = new ArrayList<Contact>();
// Select All Query
String selectQuery = "SELECT * FROM contacts ORDER BY name";

SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Contact contact = new Contact();
contact.setID(Integer.parseInt(cursor.getString(0)));
contact.setName(cursor.getString(1));
contact.setImage(cursor.getBlob(2));
// Adding contact to list
contactList.add(contact);
} while (cursor.moveToNext());
}
// close inserting data from database
db.close();
// return contact list
return contactList;

}

// Updating single contact
public int updateContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();

ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_IMAGE, contact.getImage());

// updating row
return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });

}

// Deleting single contact
public void deleteContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });
db.close();
}

// Getting contacts Count
public int getContactsCount() {
String countQuery = "SELECT * FROM " + TABLE_CONTACTS;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();

// return count
return cursor.getCount();
}
}


//SQLiteDemoActivity.java file
package com.example.sqliteimagedemo;

import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;

public class SQLiteDemoActivity extends Activity {
ArrayList<Contact> imageArry = new ArrayList<Contact>();
ContactImageAdapte adapter;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

DataBaseHandler db = new DataBaseHandler(this);
// get image from drawable
Bitmap image = BitmapFactory.decodeResource(getResources(),
R.drawable.camera);

// convert bitmap to byte
ByteArrayOutputStream stream = new ByteArrayOutputStream();
image.compress(Bitmap.CompressFormat.JPEG, 100, stream);
byte imageInByte[] = stream.toByteArray();

// Inserting Contacts

Log.d("Insert: ", "Inserting ..");
db.addContact(new Contact("FaceBook", imageInByte));

// display main List view bcard and contact name

// Reading all contacts from database

List<Contact> contacts = db.getAllContacts();
for (Contact cn : contacts) {
String log = "ID:" + cn.getID() + " Name: " + cn.getName() + " ,Image: " + cn.getImage();

// Writing Contacts to log
Log.d("Result: ", log);
//add contacts data in arrayList
imageArry.add(cn);

}

adapter = new ContactImageAdapte(this, R.layout.screen_list,
imageArry);
ListView dataList = (ListView) findViewById(R.id.list);
dataList.setAdapter(adapter);
}
}


//Contact.java
package com.example.sqliteimagedemo;

public class Contact {

// private variables
int _id;
String _name;
byte[] _image;

// Empty constructor
public Contact() {

}

// constructor
public Contact(int keyId, String name, byte[] image) {
this._id = keyId;
this._name = name;
this._image = image;

}

// constructor
public Contact(String name, byte[] image) {
this._name = name;
this._image = image;
}

// getting ID
public int getID() {
return this._id;
}

// setting id
public void setID(int keyId) {
this._id = keyId;
}

// getting name
public String getName() {
return this._name;
}

// setting name
public void setName(String name) {
this._name = name;
}

// getting phone number
public byte[] getImage() {
return this._image;
}

// setting phone number
public void setImage(byte[] image) {
this._image = image;
}
}

ContactImageAdapter.java 

package com.example.sqliteimagedemo;

import java.io.ByteArrayInputStream;
import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class ContactImageAdapte extends ArrayAdapter<Contact>{
Context context;
int layoutResourceId;
ArrayList<Contact> data=new ArrayList<Contact>();
public ContactImageAdapte(Context context, int layoutResourceId, ArrayList<Contact> data) {
super(context, layoutResourceId, data);
this.layoutResourceId = layoutResourceId;
this.context = context;
this.data = data;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
ImageHolder holder = null;
if(row == null)
{
LayoutInflater inflater = ((Activity)context).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
holder = new ImageHolder();
holder.txtTitle = (TextView)row.findViewById(R.id.txtTitle);
holder.imgIcon = (ImageView)row.findViewById(R.id.imgIcon);
row.setTag(holder);
}
else
{
holder = (ImageHolder)row.getTag();
}
Contact picture = data.get(position);
holder.txtTitle.setText(picture ._name);
//convert byte to bitmap take from contact class
byte[] outImage=picture._image;
ByteArrayInputStream imageStream = new ByteArrayInputStream(outImage);
Bitmap theImage = BitmapFactory.decodeStream(imageStream);
holder.imgIcon.setImageBitmap(theImage);
return row;
}
static class ImageHolder
{
ImageView imgIcon;
TextView txtTitle;
}
}

main.xml中

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ListView
android:id="@+id/list"
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="0.55" >
</ListView>
</LinearLayout>

screen_list.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
android:padding="10dp" >
<ImageView
android:id="@+id/imgIcon"
android:layout_width="0dp"
android:layout_height="100dp"
android:layout_weight="0.71"
android:gravity="center_vertical" />
<TextView
android:id="@+id/txtTitle"
android:layout_width="80dp"
android:layout_height="fill_parent"
android:gravity="center_vertical"
android:textSize="14sp"
android:layout_marginLeft="7dp" />
</LinearLayout>

错误讯息：

08-26 00:33:24.366: E/AndroidRuntime(977): Process: com.example.sqliteimagedemo, PID: 977
08-26 00:33:24.366: E/AndroidRuntime(977): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.sqliteimagedemo/com.example.sqliteimagedemo.DataBaseHandler}: java.lang.InstantiationException: can't instantiate class com.example.sqliteimagedemo.DataBaseHandler; no empty constructor
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread.access$900(ActivityThread.java:161)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.os.Handler.dispatchMessage(Handler.java:102)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.os.Looper.loop(Looper.java:157)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread.main(ActivityThread.java:5356)
08-26 00:33:24.366: E/AndroidRuntime(977):  at java.lang.reflect.Method.invokeNative(Native Method)
08-26 00:33:24.366: E/AndroidRuntime(977):  at java.lang.reflect.Method.invoke(Method.java:515)
08-26 00:33:24.366: E/AndroidRuntime(977):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
08-26 00:33:24.366: E/AndroidRuntime(977):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
08-26 00:33:24.366: E/AndroidRuntime(977):  at dalvik.system.NativeStart.main(Native Method)
08-26 00:33:24.366: E/AndroidRuntime(977): Caused by: java.lang.InstantiationException: can't instantiate class com.example.sqliteimagedemo.DataBaseHandler; no empty constructor
08-26 00:33:24.366: E/AndroidRuntime(977):  at java.lang.Class.newInstanceImpl(Native Method)
08-26 00:33:24.366: E/AndroidRuntime(977):  at java.lang.Class.newInstance(Class.java:1208)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
08-26 00:33:24.366: E/AndroidRuntime(977):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2222)
08-26 00:33:24.366: E/AndroidRuntime(977):  ... 11 more

1 个答案:

答案 0 :(得分：1)

在某个地方，您试图在指向startActivity()的{​​{1}}上致电Intent。此外，您的清单中必须有一个com.example.sqliteimagedemo.DataBaseHandler元素，声称<activity>是一项活动（否则，您会遇到其他错误）。但是，com.example.sqliteimagedemo.DataBaseHandler不是活动。

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