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データベースファイルへのアクセスに問題がありましたが、どこに問題があるのか正確にはわかりません。私はそれが、主なアクティビティクラスで、適切なタイミングでIntDatabaseHelperのインスタンスを作成しないことと関係していると思っていますが、何が間違っているのか正確には分かりません。すべての私のコードと私のLogcatの出力は以下の通りです。SQliteデータベースファイルがロードされていません
MainActivity
public class MainActivity extends AppCompatActivity {
IntDataBaseHelper intDataBaseHelper;
ListView lstJob;
ArrayAdapter<String> mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
intDataBaseHelper = new IntDataBaseHelper(this);
/*create instance of db helper and jobs
Create the database (only if it doesn't exists)
does so by copying from the assets */
LoadJobList();
if (CopyDBFromAssets.createDataBase(this,IntDataBaseHelper.DB_TABLE)) {
// problem area
// Get the data from the database
lstJob = (ListView) findViewById(R.id.lstJob);
ArrayList<String> jobs = intDataBaseHelper.getJobList();
for (String s : jobs) {
Log.d("JobList ", "Found Job " + s);
}
} else {
throw new RuntimeException("No Usable Database exists or was copied from the assets.");
}
}
// loads job to screen
public void LoadJobList() {
ArrayList<String> JobList = intDataBaseHelper.getJobList();
if (mAdapter == null) {
mAdapter = new ArrayAdapter<>(this,R.layout.header,R.id.header);
mAdapter = new ArrayAdapter<>(this,R.layout.row,R.id.BtnComplete,JobList);
mAdapter = new ArrayAdapter<>(this, R.layout.row, R.id.Job_name,JobList);
lstJob.setAdapter(mAdapter);
} else
{
mAdapter.clear();
mAdapter.addAll(JobList);
mAdapter.notifyDataSetChanged();
}
}
}
IntDataBase
public class IntDataBaseHelper extends SQLiteOpenHelper{
private static String DB_PATH ="//data/data/com.example.joelg.clapp/databases";
public static String DB_NAME = "JobList.db";
public static String DB_COLUMN = "jobNM";
public static String DB_TABLE = "job";
private static String DB_JOB_DETAILS = "jobDetails";
private static String DB_ISDONE = "jobIsDone";
private Context jobContext;
private SQLiteDatabase JobListDatabase;
/**
* constructor creater
*/
public IntDataBaseHelper (Context context) {
super (context, DB_NAME,null, 1);
this.jobContext = context;
DB_PATH = jobContext.getDatabasePath(DB_NAME).getPath();
}
public void OpenDataBase() {
// open the database
String JobListPath = DB_PATH;
JobListDatabase = SQLiteDatabase.openDatabase(JobListPath,null,SQLiteDatabase.OPEN_READONLY);
}
// Getting Job Count
public ArrayList<String> getJobList() {
ArrayList<String> JobList = new ArrayList<>();
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(DB_TABLE,new String[]
{DB_COLUMN},null,null,null,null,null);
while(cursor.moveToNext()){
int index = cursor.getColumnIndex(DB_COLUMN);
JobList.add(cursor.getString(index));
}
cursor.close();
db.close();
return JobList;
}
// Gets the job state if it has been competed or not
public ArrayList<String> getIsDone() {
ArrayList<String> IsDone = new ArrayList<>();
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(DB_TABLE,new String[]{DB_ISDONE},null,null,null,null,null);
while(cursor.moveToNext()){
int index = cursor.getColumnIndex(DB_ISDONE);
IsDone.add(cursor.getString(index));
}
cursor.close();
db.close();
return IsDone;
}
@Override
public synchronized void close(){
if(JobListDatabase !=null){
JobListDatabase.close();
super.close();
}
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
LogCat
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.joelg.clapp/com.example.joelg.clapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.example.joelg.clapp.MainActivity.LoadJobList(MainActivity.java:55)
at com.example.joelg.clapp.MainActivity.onCreate(MainActivity.java:34)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
At com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
[NullPointerExceptionとは何ですか？どうすれば修正できますか？]（https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix - ） –