android - 无法从片段中的 SQLite 获取数据
问题描述
我在 Android Studio 中创建了一个 SQLite 数据库，我想将数据从 EditText 插入到表中，并将该数据传递给另一个 Activity。当我在一个活动上执行此操作并尝试从另一个活动中获取时，它正在工作。但是当我尝试从另一个片段中获取数据时，我得到了一个错误。
我的数据库助手类
package fragments;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class createDBHelper extends SQLiteOpenHelper {
public static final String KEY_ID = "_id";
public static final String ITEM_NAME_COLUMN = "ITEM_NAME_COLUMN";
public static final String ITEM_GRADE_COLUMN = "ITEM_GRADE_COLUMN";
public static final String ITEM_CATEGORY_COLUMN = "ITEM_CATEGORY_COLUMN";
public static final String DATABASE_NAME = "myItemDatabase.db";
public static final String DATABASE_TABLE = "ItemInfo";
public static final int DATABASE_VERSION = 7;
private static final String DATABASE_CREATE ="create table " + DATABASE_TABLE + " (" +
KEY_ID + " text, " +
ITEM_NAME_COLUMN + " text, " +
ITEM_GRADE_COLUMN + " text);";
public createDBHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL((DATABASE_CREATE));
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w("TaskDBAdapter", "Upgrading from version" +
oldVersion + ",which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
public boolean insertData(String firstname,String lastname,String message){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues(); //instance of class
contentValues.put(KEY_ID,firstname);//2 parameters(Column name in which you
contentValues.put(ITEM_NAME_COLUMN,lastname);//2 parameters(Column name in which you
contentValues.put(ITEM_GRADE_COLUMN,message);//2 parameters(Column name in which you
//you want to insert data
// and second is the value itself
long result = db.insert(DATABASE_TABLE,null,contentValues);
if(result == -1) {
return false;
}
else {
return true;
}
}//ends insertData functin
public Cursor getAllData(){
SQLiteDatabase db = this.getWritableDatabase();
Cursor result = db.rawQuery("select * from " + DATABASE_TABLE,null);
return result;
}//ends cursor
public boolean updateData(String id,String firstname,String lastname,String credits){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(KEY_ID,id);
contentValues.put(ITEM_NAME_COLUMN,firstname);//2 parameters(Column name in which you
//you want to insert data
// and second is the value itself
contentValues.put(ITEM_GRADE_COLUMN, credits);
db.update(DATABASE_TABLE,contentValues,"_id = ?",new String[]{id});
return true;
}
public Integer deleteData(){
SQLiteDatabase db = this.getWritableDatabase();
return db.delete(DATABASE_TABLE,null,null);
}
}
我输入数据的活动
package fragments;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.navigation.ui.AppBarConfiguration;
import android.app.ActionBar;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import com.example.workflowbexfa.R;
public class createMessage extends AppCompatActivity implements View.OnClickListener {
public static final int REQUEST_CODE = 1;
createDBHelper myDataBase= new createDBHelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_message);
getSupportActionBar().hide();
ImageView imageViewgoback=(ImageView) findViewById(R.id.button_back);
imageViewgoback.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
finish();
}
});
EditText receiver_id= findViewById(R.id.receiver_id);
final String receiver=receiver_id.getText().toString();
EditText mailcontent= findViewById(R.id.mail_content);
final String mail_content=mailcontent.getText().toString();
ImageView imageViewsend=(ImageView) findViewById(R.id.button_send);
imageViewsend.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
myDataBase.deleteData();
EditText receiver_id= findViewById(R.id.receiver_id);
final String receiver=receiver_id.getText().toString();
EditText mailcontent= findViewById(R.id.mail_content);
final String mail_content=mailcontent.getText().toString();
EditText subjectedit=findViewById(R.id.subjectedit);
final String subjectcontext=subjectedit.getText().toString();
myDataBase.insertData(receiver,subjectcontext,mail_content);
//myDataBase.insertData("Tolgaaaaaasa","TUTAR");
//myDataBase.insertData("TUTAAAAR","TOLGAAA");
Intent intent = new Intent(createMessage.this,db_deneme.class);
startActivity(intent);
}
});
ImageView imageViewattach=(ImageView) findViewById(R.id.attach);
imageViewattach.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent chooseFile = new Intent(Intent.ACTION_GET_CONTENT);
chooseFile.setType("*/*");
chooseFile = Intent.createChooser(chooseFile, "Choose a file");
startActivity(chooseFile);
}
});
}
@Override
public void onClick(View view) {
}
}
当我这样做时没有问题
package fragments;
import androidx.appcompat.app.AppCompatActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.widget.TextView;
import com.example.workflowbexfa.R;
import java.util.ArrayList;
import java.util.List;
import static fragments.createDBHelper.ITEM_GRADE_COLUMN;
import static fragments.createDBHelper.ITEM_NAME_COLUMN;
import static fragments.createDBHelper.KEY_ID;
public class db_deneme extends AppCompatActivity {
createDBHelper myDataBase= new createDBHelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_db_deneme);
TextView id_text=(TextView) findViewById(R.id.textView10);
TextView id_text2=(TextView) findViewById(R.id.textView11);
TextView id_text3=(TextView) findViewById(R.id.textView3);
Cursor resultset= myDataBase.getAllData();
List<String > myList= new ArrayList();
if (resultset.moveToFirst()) {
while(!resultset.isAfterLast()){
String dbdeneme=resultset.getString(resultset.getColumnIndex(KEY_ID));
myList.add(dbdeneme);
String dbdeneme2=resultset.getString(resultset.getColumnIndex(ITEM_NAME_COLUMN));
myList.add(dbdeneme2);
String dbdeneme3=resultset.getString(resultset.getColumnIndex(ITEM_GRADE_COLUMN));
myList.add(dbdeneme3);
resultset.moveToNext();
}
}
id_text.setText(myList.get(0));
id_text2.setText(myList.get(1));
id_text3.setText(myList.get(2));
//id_text2.setText(myList.get(3));
}
}
但是当我尝试在这个片段中这样做时
package fragments;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.ListView;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import com.example.workflowbexfa.R;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import static fragments.createDBHelper.ITEM_GRADE_COLUMN;
import static fragments.createDBHelper.ITEM_NAME_COLUMN;
import static fragments.createDBHelper.KEY_ID;
public class Sentfragment extends Fragment implements View.OnClickListener {
createDBHelper myDataBase= new createDBHelper(getActivity());
List<SentMessage> sentMessageList;
ListView listView;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState ){
View rootView = inflater .inflate(R.layout.sentfragment,container,false);
listView = (ListView) rootView.findViewById(R.id.listView_sent);
((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("Gönderilenler");
sentMessageList=new ArrayList<>();
List<String > myList= new ArrayList();
//sentMessageList.add(new SentMessage(R.drawable.sentmailicon,"Alıcı:Ahmet","Üzgünüm şu anda cevap veremiyorum.","12:00","Proje Hk.",R.drawable.staricon));
Cursor resultset=myDataBase.getAllData();
if (resultset.moveToFirst()) {
while(!resultset.isAfterLast()){
while(!resultset.isAfterLast()){
String dbdeneme=resultset.getString(resultset.getColumnIndex(KEY_ID));
myList.add(dbdeneme);
String dbdeneme2=resultset.getString(resultset.getColumnIndex(ITEM_NAME_COLUMN));
myList.add(dbdeneme2);
String dbdeneme3=resultset.getString(resultset.getColumnIndex(ITEM_GRADE_COLUMN));
myList.add(dbdeneme3);
resultset.moveToNext();
}
}
}
List<HashMap<String, String>> listItems = new ArrayList<>();
final SentMyCustomListAdapter adapter=new SentMyCustomListAdapter(getContext(),R.layout.my_list_item_sent,sentMessageList);
listView.setAdapter(adapter);
ImageView imageViewCreate=(ImageView) rootView.findViewById(R.id.addicon);
imageViewCreate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
sentMessageList.add(new SentMessage(R.drawable.sentmailicon,"asd","Üzgünüm şu anda cevap veremiyorum.","12:00","Proje Hkkk.",R.drawable.staricon));
adapter.notifyDataSetChanged();
}
});
return rootView;
}
@Override
public void onClick(View view) {
}
}
我得到这个错误
2020-08-17 17:31:02.551 3495-3495/? E/Zygote: GL_OOM reserved vma failed, errno:22
2020-08-17 17:31:02.687 3495-3495/? E/e.workflowbexf: Unknown bits set in runtime_flags: 0x28000
2020-08-17 17:31:02.749 3495-3495/? E/RefClass: java.lang.reflect.InvocationTargetException
2020-08-17 17:31:03.096 3495-3495/com.example.workflowbexfa E/PswScreenModeFeature: failed to get oppposcreenmode service:binder null
2020-08-17 17:31:03.096 3495-3495/com.example.workflowbexfa E/PswScreenModeFeature: failed to get oppposcreenmode service:interface null.
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: >>> msg's executing time is too long
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Blocked msg = { when=-2s30ms what=0 target=android.view.Choreographer$FrameHandler callback=android.view.Choreographer$FrameDisplayEventReceiver } , cost = 2014 ms
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: >>>Current msg List is:
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <1> = { when=-14h29m13s993ms what=0 target=android.view.ViewRootImpl$ViewRootHandler callback=android.view.-$$Lambda$ViewRootImpl$7A_3tkr_Kw4TZAeIUGVlOoTcZhg }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <2> = { when=-2s5ms what=0 target=android.view.ViewRootImpl$ViewRootHandler callback=androidx.appcompat.app.AppCompatDelegateImpl$2 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <3> = { when=-1s998ms what=0 target=android.view.ViewRootImpl$ViewRootHandler callback=androidx.appcompat.app.ToolbarActionBar$1 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <4> = { when=-1s957ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$2 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <5> = { when=-1s956ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$1 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <6> = { when=-1s951ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$2 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <7> = { when=-1s951ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$1 }
2020-08-17 17:31:05.962 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <8> = { when=-1s947ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$2 }
2020-08-17 17:31:05.963 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <9> = { when=-1s946ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$1 }
2020-08-17 17:31:05.963 3495-3495/com.example.workflowbexfa E/ANR_LOG: Current msg <10> = { when=-1s943ms what=0 target=android.os.Handler callback=androidx.core.content.res.ResourcesCompat$FontCallback$2 }
2020-08-17 17:31:05.963 3495-3495/com.example.workflowbexfa E/ANR_LOG: >>>CURRENT MSG DUMP OVER<<<
2020-08-17 17:31:08.374 3495-3495/com.example.workflowbexfa E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.workflowbexfa, PID: 3495
java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File android.content.Context.getDatabasePath(java.lang.String)' on a null object reference
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:371)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:317)
at fragments.createDBHelper.getAllData(createDBHelper.java:88)
at fragments.Sentfragment.onCreateView(Sentfragment.java:55)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1356)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1434)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1497)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2169)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1992)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1947)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:899)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:238)
at android.app.ActivityThread.main(ActivityThread.java:7864)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:998)
解决方案
我通过不在 Sentfragment 中而是在 onCreateView 中初始化我的 DBHelper 解决了这个问题。
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