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データベースからのデータのリストビューを処理するクラスにインテントをロードしようとすると、「NullPointerException」が発生します。リストビューに関してはまったくの初心者なので、どこが間違っているのか教えていただければ幸いです。

null ポインターは、カーソルがある最初の行の位置にデータが見つからなかったことが原因であると考えていましたが、logcat を見ると、XML レイアウトの「エントリ」に問題があると思いますか?

リストビューの私のクラスは次のとおりです。

package com.example.sqliteexample;



import android.app.Activity;
import android.app.ListActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.widget.ListView;

public class SQLView extends Activity {

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    HotOrNot H = new HotOrNot(this, null, null);

    setContentView(R.layout.layout);
     ListView listContent = (ListView)findViewById(R.id.contentList);

     HotOrNot Content = new HotOrNot(this, null, null);

    Cursor cursor = Content.getData();

    startManagingCursor(cursor);

    @SuppressWarnings("static-access")
    String [] from = new String [] {H.KEY_NAME, H.KEY_HOTNESS};
    int [] to = new int [] {R.id.txtName, R.id.txtAge};

    @SuppressWarnings("deprecation")
    SimpleCursorAdapter cursorAdapter = new SimpleCursorAdapter(this, R.layout.entries, cursor, from, to);

    listContent.setAdapter(cursorAdapter);

DB ハンドラー クラスの「getData」メソッド:

public Cursor getData() {

        String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
        Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);


        return c;

HotOrNot DB ハンドラ クラス:

package com.example.sqliteexample;

import android.app.ListActivity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.ListView;

public class HotOrNot {

public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "persons_name";
public static final String KEY_HOTNESS = "persons_hotness";

private static String DATABASE_NAME = "HotOrNotdb";
private static String DATABASE_TABLE = "peopleTable";
private static int DATABASE_VERSION = 30;

private static DBHelper ourHelper;
private static Context ourContext;
private static SQLiteDatabase ourDatabase;

ListView listview;


public void DB_NAME(String DBName)
{
    DATABASE_NAME = DBName;

}

public String returnDB_NAME()
{
    return DATABASE_NAME;
}


public void DB_tableNAME(String DBtName)
{
    DATABASE_TABLE = DBtName;

}

public String returnDB_tNAME()
{
    return DATABASE_TABLE;
}


public void DB_NAME(int DBVersion)
{
    DATABASE_VERSION = DBVersion;

}

public int returnDB_VERSION()
{
    return DATABASE_VERSION;
}



// class constructor for context. when the object is constructed in the main programme
// the context of that class i.e 'this' is sent to this constructor to set the object context.
// null values set on SQLiteDatabase and DBhelper as there is nothing to pass from the called
// objects.
public HotOrNot (Context c, SQLiteDatabase newSQL, DBHelper BD)
{
    ourContext = c;
    ourDatabase = newSQL;
    ourHelper = BD;

}







private static class DBHelper extends SQLiteOpenHelper
{
    public DBHelper(Context context) {
        super(context, KEY_NAME, null, DATABASE_VERSION);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {


        db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" +
                KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                KEY_NAME + " TEXT NOT NULL, " +
                KEY_HOTNESS + " TEXT NOT NULL);"

                );


    }

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

        db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
        onCreate(db);
    }
}



    public HotOrNot open() throws SQLException
    {

        ourHelper = new DBHelper(ourContext);
        ourDatabase = ourHelper.getWritableDatabase();
        return this;

    }

    public void close()
    {
        ourHelper.close();

    }

    public long createEntry(String name, String hotness) {


        ContentValues cv = new ContentValues();
        cv.put(KEY_NAME, name);
        cv.put(KEY_HOTNESS, hotness);
        return ourDatabase.insert(DATABASE_TABLE, null, cv);

    }

    public Cursor getData() {

        String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
        Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
        //String result = "";

        //int iRow = c.getColumnIndex(KEY_ROWID);
        //int iName = c.getColumnIndex(KEY_NAME);
        //int ihotness = c.getColumnIndex(KEY_HOTNESS);

        //for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext())
        //{
            //result = result + c.getString(iRow) + "" + c.getString(iName) + "" + c.getString(ihotness);

        //}

        //c.close();

        return c;
    }

    public String getName(long l) {

        String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
        Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "=" + l, null, null, null, null);
        if(c != null)
        {
            // move to the selected row
        c.moveToFirst();
        String name = c.getString(1);
        return name;
        }
        return null;

    }


    public String getHotness(long l) {

        String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
        Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "=" + l, null, null, null, null);
        if(c != null)
        {
            // move to the selected row
        c.moveToFirst();
        String hotness = c.getString(2);
        return hotness;

    }
        return null;


    }

    public void updateEntry(long newl, String nameEdit, String hotnessEdit) {
    ContentValues cvUpdate = new ContentValues();

    cvUpdate.put(KEY_NAME, nameEdit);
    cvUpdate.put(KEY_HOTNESS, hotnessEdit);

    ourDatabase.update(DATABASE_TABLE, cvUpdate, KEY_ROWID + "=" + newl, null);


    }

    public void delID(long l) {
        ourDatabase.delete(DATABASE_TABLE, KEY_ROWID + "=" + l, null);

    }

}

リストビューの私の XML レイアウト:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<TextView
    android:id="@+id/txtName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Name:" />

<TextView
    android:id="@+id/txtAge"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Age:" />

</LinearLayout>

リストビュー XML レイアウト:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ListView
    android:id="@+id/contentList"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >
</ListView>

</LinearLayout>

ログキャット:

01-11 00:23:26.655: D/AndroidRuntime(272): Shutting down VM
01-11 00:23:26.655: W/dalvikvm(272): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
01-11 00:23:26.675: E/AndroidRuntime(272): FATAL EXCEPTION: main
01-11 00:23:26.675: E/AndroidRuntime(272): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sqliteexample/com.example.sqliteexample.SQLView}: java.lang.NullPointerException
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.os.Looper.loop(Looper.java:123)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread.main(ActivityThread.java:4627)
01-11 00:23:26.675: E/AndroidRuntime(272):  at java.lang.reflect.Method.invokeNative(Native Method)
01-11 00:23:26.675: E/AndroidRuntime(272):  at java.lang.reflect.Method.invoke(Method.java:521)
01-11 00:23:26.675: E/AndroidRuntime(272):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-11 00:23:26.675: E/AndroidRuntime(272):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-11 00:23:26.675: E/AndroidRuntime(272):  at dalvik.system.NativeStart.main(Native Method)
01-11 00:23:26.675: E/AndroidRuntime(272): Caused by: java.lang.NullPointerException
01-11 00:23:26.675: E/AndroidRuntime(272):  at com.example.sqliteexample.HotOrNot.getData(HotOrNot.java:143)
01-11 00:23:26.675: E/AndroidRuntime(272):  at com.example.sqliteexample.SQLView.onCreate(SQLView.java:24)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-11 00:23:26.675: E/AndroidRuntime(272):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
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2 に答える 2

3

に電話するのを忘れただけですopen()。

HotOrNot Content = new HotOrNot(this, null, null);
Content.open();
Cursor cursor = Content.getData();

(ただし、Java の命名規則については、状態変数が小文字で始まる必要があることをお読みください。)

于 2013-01-11T00:33:11.377 に答える
0 
public HotOrNot (Context c, SQLiteDatabase newSQL, DBHelper BD)
{
    ourContext = c;
    ourDatabase = newSQL;
    ourHelper = BD;

}

ここでは、onCreate で null をSQLiteDatabase

HotOrNot H = new HotOrNot(this, null, null);
于 2013-01-11T00:34:27.913 に答える