javaで別のクラスを作成する際に問題があります コードのこの部分があります
private class Read_from_db extends AsyncTask <String, Long, Void> {
private final ProgressDialog dialog = new ProgressDialog(Read.this);
// can use UI thread here
protected void onPreExecute() {
this.dialog.setMessage("Wait\nSome SLOW job is being done...");
this.dialog.show();
}
@Override
protected Void doInBackground(String... arg0) {
// TODO Auto-generated method stub
try {
//txtMsg.append("\n");
// obtain a list of from DB
String TABLE_NAME = "classicpoems__poet_header";
String COLUMN_ID = "_id";
// String _ID = "_id";
String COLUMN_NAME = "poet_name";
String COLUMN_CENTURY = "century_start";
String [] columns ={COLUMN_ID,COLUMN_NAME,COLUMN_CENTURY};
Cursor c = db.query(TABLE_NAME,columns,null, null, null, null, COLUMN_ID);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Read.this, R.layout.list_item, c,
new String[] {COLUMN_ID,COLUMN_NAME,COLUMN_CENTURY}, new int[] {R.id.list_item_text_id,R.id.list_item_text_main,R.id.list_item_text_sub}, 0);
ListView list = (ListView) findViewById(R.id.list_poet_name);
list.setAdapter(adapter);
} catch (Exception e) {
//Toast.makeText(Read.this, e.getMessage(), 1).show();
Log.i(TAG, e.getMessage());
}
db.close();
return null;
}
// can use UI thread here
protected void onPostExecute(final Void unused) {
if (this.dialog.isShowing()) {
this.dialog.dismiss();
}
// cleaning-up, all done
this.dialog.setMessage("Done");
}
}
これは、アクティビティがロードされるたびに繰り返さなければなりません (ただし、TABLE_NAME
andR.id.list_poet_name
columns
と .. などのいくつかの変更があります)。方法がわからない..(試してみましたが、常にエラーが発生します。たとえば、SimpleCursorAdapter
ここでコンテキストを定義する方法やトーストを機能させる方法がわかりません。このコードを別のクラスに変換する方法を教えてください。
これが私のクラスコードです
package co.tosca.persianpoem;
import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
public class Get_data extends AsyncTask<String, Long, Void> {
//Context context;
public String TABLE_NAME;
public String COLUMN_ID;
public String COLUMN_NAME;
public String COLUMN_CENTURY;
public String[] columns;
public int target;
private String DATABASE_NAME;
private static final String SDcardPath = Environment.getExternalStorageDirectory().getPath();
private String DbPath = SDcardPath + "/Tosca/" + DATABASE_NAME;
private static final String TAG ="DatabaseHelper";
private SQLiteDatabase db;
private ProgressDialog dialog;
private Activity callingActivity;
public int adapter_list;
//public Get_data(Context context){
// this.context=context;
// DATABASE_NAME="persian_poem.db";
//}
public Get_data(Activity activity) {
callingActivity = activity;
}
public Get_data() {
TABLE_NAME="classicpoems__poet_header";
COLUMN_ID="_id";
COLUMN_NAME = "poet_name";
}
@Override
protected void onPreExecute() {
this.dialog.setMessage("Wait\nSome SLOW job is being done...");
this.dialog.show();
}
@Override
protected Void doInBackground(String... arg0) {
// TODO Auto-generated method stub
try {
// obtain a list of from DB
// String TABLE_NAME = "classicpoems__poet_header";
// String COLUMN_ID = "_id";
// String _ID = "_id";
// String COLUMN_NAME = "poet_name";
// String COLUMN_CENTURY = "century_start";
// String [] columns ={COLUMN_ID,COLUMN_NAME,COLUMN_CENTURY};
Cursor c = db.query(TABLE_NAME,columns,null, null, null, null, COLUMN_ID);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(callingActivity, adapter_list, c,
new String[] {COLUMN_ID,COLUMN_NAME,COLUMN_CENTURY}, new int[] {R.id.list_item_text_id,R.id.list_item_text_main,R.id.list_item_text_sub}, 0);
ListView list = (ListView)callingActivity.findViewById(target);
list.setAdapter(adapter);
} catch (Exception e) {
Toast.makeText(callingActivity, e.getMessage(), 1).show();
Log.i(TAG, e.getMessage());
}
db.close();
return null;
}
protected void onPostExecute(final Void unused) {
dialog.dismiss();
}
}
使用したいときは、このコードを使用します
enter code here Get_data poet_name=new Get_data();
poet_name.TABLE_NAME="classicpoems__poet_header";
poet_name.COLUMN_ID = "_id";
poet_name.COLUMN_NAME = "poet_name";
poet_name.COLUMN_CENTURY = "century_start";
poet_name.columns =new String[]{"_id","poet_name","century_start"};
poet_name.adapter_list=R.layout.list_item;
poet_name.target=R.id.list_poet_name;
poet_name.execute();
しかし、エラーが発生します..間違いを見つけるのを手伝ってもらえますか?
初期コードを に変更しまし Get_data poet_name=new Get_data(this);
たが、エラーが発生していますが、これは logcat の一部です
01-06 04:25:32.262: E/AndroidRuntime(3244): FATAL EXCEPTION: main
01-06 04:25:32.262: E/AndroidRuntime(3244): java.lang.RuntimeException: Unable to start activity ComponentInfo{co.tosca.persianpoem/co.tosca.persianpoem.Read}: java.lang.NullPointerException
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread.access$600(ActivityThread.java:127)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.os.Handler.dispatchMessage(Handler.java:99)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.os.Looper.loop(Looper.java:137)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread.main(ActivityThread.java:4441)
01-06 04:25:32.262: E/AndroidRuntime(3244): at java.lang.reflect.Method.invokeNative(Native Method)
01-06 04:25:32.262: E/AndroidRuntime(3244): at java.lang.reflect.Method.invoke(Method.java:511)
01-06 04:25:32.262: E/AndroidRuntime(3244): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-06 04:25:32.262: E/AndroidRuntime(3244): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-06 04:25:32.262: E/AndroidRuntime(3244): at dalvik.system.NativeStart.main(Native Method)
01-06 04:25:32.262: E/AndroidRuntime(3244): Caused by: java.lang.NullPointerException
01-06 04:25:32.262: E/AndroidRuntime(3244): at co.tosca.persianpoem.Get_data.onPreExecute(Get_data.java:54)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:561)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.os.AsyncTask.execute(AsyncTask.java:511)
01-06 04:25:32.262: E/AndroidRuntime(3244): at co.tosca.persianpoem.Read.onCreate(Read.java:65)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.Activity.performCreate(Activity.java:4465)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-06 04:25:32.262: E/AndroidRuntime(3244): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
01-06 04:25:32.262: E/AndroidRuntime(3244): ... 11 more