从使用 SearchView 小部件查询的外部 SQlite 数据库填充 ListView - Android

Question

我正在尝试在 ListView 小部件中显示我的数据库中的数据。使用 SearchView 小部件查询数据库。

这是我的 SQlite 开放帮助程序类的代码：

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;


import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class DataBaseHelper extends SQLiteOpenHelper {

//The Android's default system path of your application database.

private static String DB_NAME = "DB.sqlite";

private SQLiteDatabase myDB;

private final Context myContext;


/**
 * Constructor
 * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
 * @param context
 */
public DataBaseHelper(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
}

/**
 * Creates a empty database on the system and rewrites it with your own database.
 * */
public void createDataBase() throws IOException {

    boolean dbExist = checkDataBase();

    if(dbExist){
        //do nothing - database already exist
    }else{

        //By calling this method and empty database will be created into the default system path
        //of your application so we are gonna be able to overwrite that database with our database.
        this.getReadableDatabase();

        try {

            copyDataBase();

        } catch (IOException e) {

            throw new Error("Error copying database");

        }
    }

}

/**
 * Check if the database already exist to avoid re-copying the file each time you open the application.
 * @return true if it exists, false if it doesn't
 */
private boolean checkDataBase(){

    SQLiteDatabase checkDB = null;

    try{
        String myPath = myContext.getDatabasePath(DB_NAME).getPath();
        checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

    }catch(SQLiteException e){

        //database does't exist yet.

    }

    if(checkDB != null){

        checkDB.close();

    }

    return checkDB != null ? true : false;
}


/**
 * Copies your database from your local assets-folder to the just created empty database in the
 * system folder, from where it can be accessed and handled.
 * This is done by transfering bytestream.
 * */
private void copyDataBase() throws IOException{

    //Open your local db as the input stream
    InputStream myInput = myContext.getAssets().open(DB_NAME);

    // Path to the just created empty db
    String outFileName = myContext.getDatabasePath(DB_NAME).getPath();

    //Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);

    //transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myInput.read(buffer))>0){
        myOutput.write(buffer, 0, length);
    }

    //Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();

}

public void openDataBase() throws SQLException {

    //Open the database
    String myPath = myContext.getDatabasePath(DB_NAME).getPath();
    myDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

}

@Override
public synchronized void close() {

    if(myDB != null)
        myDB.close();

    super.close();

}

@Override
public void onCreate(SQLiteDatabase myDataBase) {

}


@Override
public void onUpgrade(SQLiteDatabase myDataBase, int oldVersion, int newVersion) {

}



public Cursor getC(String animal) {
    Cursor c;
    c=myDB.rawQuery("SELECT * FROM Table where animal MATCH ?", new String [] {animal});
    c.moveToFirst();

    return c;
}




}


// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.

这是我的光标适配器类的代码：

import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.TextView;


public class TodoCursorAdapter extends CursorAdapter {

private LayoutInflater mInflater;

public TodoCursorAdapter(Context context, Cursor c, int flags) {
    super(context, c, flags);
    mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

/* ... */

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
    return mInflater.inflate(R.layout.search_item, parent, false);
}



// The bindView method is used to bind all data to a given view
// such as setting the text on a TextView.

@Override
public void bindView(View view, Context context, Cursor cursor) {
    TextView content = (TextView) view.findViewById(R.id.résultatAnimal);
    content.setText(cursor.getString(2));

    }
}

这是我的可搜索活动代码：

import android.app.ListActivity;
import android.app.SearchManager;
import android.content.Intent;
import android.database.SQLException;
import android.os.Bundle;
import android.widget.ListView;


import java.io.IOException;


public class searchableActivity extends ListActivity {



@Override
public void onCreate(Bundle savedInstanceState) {

    DataBaseHelper myDbHelper = new DataBaseHelper(searchableActivity.this);

    try {

        myDbHelper.createDataBase();

    } catch (IOException ioe) {

        throw new Error("Unable to create database");

    }

    try {

        myDbHelper.openDataBase();

    }catch(SQLException sqle){

        throw sqle;

    }


    super.onCreate(savedInstanceState);



    // Get the intent, verify the action and get the query
    Intent intent = getIntent();
    if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
        String query = intent.getStringExtra(SearchManager.QUERY);
        //myDbHelper.getC(query).getString(2);
        // Find ListView to populate
        ListView AnimalListe = (ListView) findViewById(R.id.list);
// Setup cursor adapter using cursor from last step
        TodoCursorAdapter todoAdapter = new TodoCursorAdapter(this, myDbHelper.getC(query), 0);
// Attach cursor adapter to the ListView
        AnimalListe.setAdapter(todoAdapter);
    }

    myDbHelper.close();
}
}

当我在 SearchView 小部件中启动搜索时，出现错误“NULL POINTER EXCEPTION”并且应用程序崩溃。为什么？

Answer 1

请首先检查是否在 Android Monitor 中创建数据库。 我认为您的代码是编写的，但有时会在 copydatabase 中编写以下代码。

private void copyDataBase() 抛出 IOException{

//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);

// Path to the just created empty db
String outFileName = myContext.getDatabasePath(DB_NAME).getPath();

File file=outFileName;

if(!file.isExits)
    file.mkdir();

//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);

//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
    myOutput.write(buffer, 0, length);
}

//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();

}