我正在用eclipse开发一个安卓应用。我有一个活动，当它第二次被调用时，它就崩溃了。我认为问题是由于该活动的变量仍然有值。当我们离开这个活动时，如何清除变量的值？
package com.example.anagramslayer;
import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;
public class QuestionList extends Activity implements OnClickListener{
private SQLiteAdapter mySQLiteAdapter;
ImageView header;
ImageView category;
ImageButton homeModule;
Button buttonQuestion1;
Button buttonQuestion2;
Button buttonQuestion3;
Button buttonQuestion4;
Button buttonQuestion5;
Button buttonQuestion6;
Button buttonQuestion7;
Button buttonQuestion8;
Button buttonQuestion9;
Button buttonQuestion10;
Button buttonQuestion11;
Button buttonQuestion12;
Button buttonQuestion13;
Button buttonQuestion14;
Button buttonQuestion15;
//************** init String to get each of column index in database **************
private List<String> getAnswer = new ArrayList<String>();
private List<String>getQuestion = new ArrayList<String>();
private List<String>getFlag= new ArrayList<String>();
//************** init String to get each of column index in database, used in onClick**************
private List<String> getIdListener = new ArrayList<String>();
private List<String> getFlagListener = new ArrayList<String>();
//************** var used in onClick **************
private long idListener1;
private long idListener2;
private long idListener3;
private long idListener4;
private long idListener5;
private long idListener6;
private long idListener7;
private long idListener8;
private long idListener9;
private long idListener10;
private long idListener11;
private long idListener12;
private long idListener13;
private long idListener14;
private long idListener15;
private long flagListener1;
private long flagListener2;
private long flagListener3;
private long flagListener4;
private long flagListener5;
private long flagListener6;
private long flagListener7;
private long flagListener8;
private long flagListener9;
private long flagListener10;
private long flagListener11;
private long flagListener12;
private long flagListener13;
private long flagListener14;
private long flagListener15;
private long getLevelKey;
private String flag1;
private String flag2;
private String flag3;
private String flag4;
private String flag5;
private String flag6;
private String flag7;
private String flag8;
private String flag9;
private String flag10;
private String flag11;
private String flag12;
private String flag13;
private String flag14;
private String flag15;
private String question1;
private String question2;
private String question3;
private String question4;
private String question5;
private String question6;
private String question7;
private String question8;
private String question9;
private String question10;
private String question11;
private String question12;
private String question13;
private String question14;
private String question15;
private String answer1;
private String answer2;
private String answer3;
private String answer4;
private String answer5;
private String answer6;
private String answer7;
private String answer8;
private String answer9;
private String answer10;
private String answer11;
private String answer12;
private String answer13;
private String answer14;
private String answer15;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.question_list);
//************** retrieved parameter from LevelList **************
Bundle extras = getIntent().getExtras();
getLevelKey = extras.getLong(this.getPackageName());
//************** fetch data from database **************
fetchData();
//************** init button **************
homeModule = (ImageButton) findViewById(R.id.home_button);
buttonQuestion1 = (Button) findViewById(R.id.question1);
buttonQuestion2 = (Button) findViewById(R.id.question2);
buttonQuestion3 = (Button) findViewById(R.id.question3);
buttonQuestion4 = (Button) findViewById(R.id.question4);
buttonQuestion5 = (Button) findViewById(R.id.question5);
buttonQuestion6 = (Button) findViewById(R.id.question6);
buttonQuestion7 = (Button) findViewById(R.id.question7);
buttonQuestion8 = (Button) findViewById(R.id.question8);
buttonQuestion9 = (Button) findViewById(R.id.question9);
buttonQuestion10 = (Button) findViewById(R.id.question10);
buttonQuestion11 = (Button) findViewById(R.id.question11);
buttonQuestion12 = (Button) findViewById(R.id.question12);
buttonQuestion13 = (Button) findViewById(R.id.question13);
buttonQuestion14 = (Button) findViewById(R.id.question14);
buttonQuestion15 = (Button) findViewById(R.id.question15);
homeModule.setOnClickListener(this);
buttonQuestion1.setOnClickListener(this);
buttonQuestion2.setOnClickListener(this);
buttonQuestion3.setOnClickListener(this);
buttonQuestion4.setOnClickListener(this);
buttonQuestion5.setOnClickListener(this);
buttonQuestion6.setOnClickListener(this);
buttonQuestion7.setOnClickListener(this);
buttonQuestion8.setOnClickListener(this);
buttonQuestion9.setOnClickListener(this);
buttonQuestion10.setOnClickListener(this);
buttonQuestion11.setOnClickListener(this);
buttonQuestion12.setOnClickListener(this);
buttonQuestion13.setOnClickListener(this);
buttonQuestion14.setOnClickListener(this);
buttonQuestion15.setOnClickListener(this);
//************** variable needed in onClick **************
idListener1 = Long.parseLong(getIdListener.get(0));
idListener2 = Long.parseLong(getIdListener.get(1));
idListener3 = Long.parseLong(getIdListener.get(2));
idListener4 = Long.parseLong(getIdListener.get(3));
idListener5 = Long.parseLong(getIdListener.get(4));
idListener6 = Long.parseLong(getIdListener.get(5));
idListener7 = Long.parseLong(getIdListener.get(6));
idListener8 = Long.parseLong(getIdListener.get(7));
idListener9 = Long.parseLong(getIdListener.get(8));
idListener10 = Long.parseLong(getIdListener.get(9));
idListener11 = Long.parseLong(getIdListener.get(10));
idListener12 = Long.parseLong(getIdListener.get(11));
idListener13 = Long.parseLong(getIdListener.get(12));
idListener14 = Long.parseLong(getIdListener.get(13));
idListener15 = Long.parseLong(getIdListener.get(14));
flagListener1 = Long.parseLong(getFlagListener.get(0));
flagListener2 = Long.parseLong(getFlagListener.get(1));
flagListener3 = Long.parseLong(getFlagListener.get(2));
flagListener4 = Long.parseLong(getFlagListener.get(3));
flagListener5 = Long.parseLong(getFlagListener.get(4));
flagListener6 = Long.parseLong(getFlagListener.get(5));
flagListener7 = Long.parseLong(getFlagListener.get(6));
flagListener8 = Long.parseLong(getFlagListener.get(7));
flagListener9 = Long.parseLong(getFlagListener.get(8));
flagListener10 = Long.parseLong(getFlagListener.get(9));
flagListener11 = Long.parseLong(getFlagListener.get(10));
flagListener12 = Long.parseLong(getFlagListener.get(11));
flagListener13 = Long.parseLong(getFlagListener.get(12));
flagListener14 = Long.parseLong(getFlagListener.get(13));
flagListener15 = Long.parseLong(getFlagListener.get(14));
//************** variable needed in onCreate **************
flag1 = getFlag.get(0);
flag2 = getFlag.get(1);
flag3 = getFlag.get(2);
flag4 = getFlag.get(3);
flag5 = getFlag.get(4);
flag6 = getFlag.get(5);
flag7 = getFlag.get(6);
flag8 = getFlag.get(7);
flag9 = getFlag.get(8);
flag10 = getFlag.get(9);
flag11 = getFlag.get(10);
flag12 = getFlag.get(11);
flag13 = getFlag.get(12);
flag14 = getFlag.get(13);
flag15 = getFlag.get(14);
question1 = getQuestion.get(0);
question2 = getQuestion.get(1);
question3 = getQuestion.get(2);
question4 = getQuestion.get(3);
question5 = getQuestion.get(4);
question6 = getQuestion.get(5);
question7 = getQuestion.get(6);
question8 = getQuestion.get(7);
question9 = getQuestion.get(8);
question10 = getQuestion.get(9);
question11 = getQuestion.get(10);
question12 = getQuestion.get(11);
question13 = getQuestion.get(12);
question14 = getQuestion.get(13);
question15 = getQuestion.get(14);
answer1 = getAnswer.get(0);
answer2 = getAnswer.get(1);
answer3 = getAnswer.get(2);
answer4 = getAnswer.get(3);
answer5 = getAnswer.get(4);
answer6 = getAnswer.get(5);
answer7 = getAnswer.get(6);
answer8 = getAnswer.get(7);
answer9 = getAnswer.get(8);
answer10 = getAnswer.get(9);
answer11 = getAnswer.get(10);
answer12 = getAnswer.get(11);
answer13 = getAnswer.get(12);
answer14 = getAnswer.get(13);
answer15 = getAnswer.get(14);
//************** set button **************
setButton();
//************** set level header **************
setLevelHeader();
//************** view score and hint **************
setScoreHint();
}
public void fetchData(){
//************** fetching data **************
mySQLiteAdapter = new SQLiteAdapter(getApplicationContext());
mySQLiteAdapter.openToWrite();
Cursor c = mySQLiteAdapter.getQuestionEachLevel(getLevelKey);
if(c.moveToFirst()){
do{
getIdListener.add(c.getString(0));
getAnswer.add( c.getString(1));
getQuestion.add(c.getString(2));
getFlag.add(c.getString(4));
getFlagListener.add(c.getString(4));
}while(c.moveToNext());
}
mySQLiteAdapter.close();
}
@Override
public void onClick(View v) {
switch(v.getId()){
case R.id.home_button:
startActivity(new Intent(QuestionList.this, Main.class));
break;
case R.id.question1:
if(flagListener1 == 0){
Intent newIntent1 = new Intent(this, Answering.class);
newIntent1.putExtra(this.getPackageName(), idListener1);
this.startActivity(newIntent1);}
break;
case R.id.question2:
if(flagListener2 == 0){
Intent newIntent2 = new Intent(this, Answering.class);
newIntent2.putExtra(this.getPackageName(), idListener2);
this.startActivity(newIntent2);}
break;
case R.id.question3:
if(flagListener3 == 0){
Intent newIntent3 = new Intent(this, Answering.class);
newIntent3.putExtra(this.getPackageName(), idListener3);
this.startActivity(newIntent3);}
break;
case R.id.question4:
if(flagListener4 == 0){
Intent newIntent4 = new Intent(this, Answering.class);
newIntent4.putExtra(this.getPackageName(), idListener4);
this.startActivity(newIntent4);}
break;
case R.id.question5:
if(flagListener5 == 0){
Intent newIntent5 = new Intent(this, Answering.class);
newIntent5.putExtra(this.getPackageName(), idListener5);
this.startActivity(newIntent5);}
break;
case R.id.question6:
if(flagListener6 == 0){
Intent newIntent6 = new Intent(this, Answering.class);
newIntent6.putExtra(this.getPackageName(), idListener6);
this.startActivity(newIntent6);}
break;
case R.id.question7:
if(flagListener7 == 0){
Intent newIntent7 = new Intent(this, Answering.class);
newIntent7.putExtra(this.getPackageName(), idListener7);
this.startActivity(newIntent7);}
break;
case R.id.question8:
if(flagListener8 == 0){
Intent newIntent8 = new Intent(this, Answering.class);
newIntent8.putExtra(this.getPackageName(), idListener8);
this.startActivity(newIntent8);}
break;
case R.id.question9:
if(flagListener9 == 0){
Intent newIntent9 = new Intent(this, Answering.class);
newIntent9.putExtra(this.getPackageName(), idListener9);
this.startActivity(newIntent9);}
break;
case R.id.question10:
if(flagListener10 == 0){
Intent newIntent10 = new Intent(this, Answering.class);
newIntent10.putExtra(this.getPackageName(), idListener10);
this.startActivity(newIntent10);}
break;
case R.id.question11:
if(flagListener11 == 0){
Intent newIntent11 = new Intent(this, Answering.class);
newIntent11.putExtra(this.getPackageName(), idListener11);
this.startActivity(newIntent11);}
break;
case R.id.question12:
if(flagListener12 == 0){
Intent newIntent12 = new Intent(this, Answering.class);
newIntent12.putExtra(this.getPackageName(), idListener12);
this.startActivity(newIntent12);}
break;
case R.id.question13:
if(flagListener13 == 0){
Intent newIntent13 = new Intent(this, Answering.class);
newIntent13.putExtra(this.getPackageName(), idListener13);
this.startActivity(newIntent13);}
break;
case R.id.question14:
if(flagListener14 == 0){
Intent newIntent14 = new Intent(this, Answering.class);
newIntent14.putExtra(this.getPackageName(), idListener14);
this.startActivity(newIntent14);}
break;
case R.id.question15:
if(flagListener15 == 0){
Intent newIntent15 = new Intent(this, Answering.class);
newIntent15.putExtra(this.getPackageName(), idListener15);
this.startActivity(newIntent15);}
break;
}
}
public void setLevelHeader(){
//************** set level header image **************
if(getLevelKey == 1){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level1);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_fruit);
}else if(getLevelKey == 2){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level2);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_animal);
}else if(getLevelKey == 3){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level3);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_music);
}else if(getLevelKey == 4){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level4);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_city);
}else if(getLevelKey == 5){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level5);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_sport);
}else if(getLevelKey == 6){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level6);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_food);
}else if(getLevelKey == 7){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level7);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_verb);
}else if(getLevelKey == 8){
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level8);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_province);
}else{
header = (ImageView) findViewById(R.id.level_header);
header.setImageResource(R.drawable.header_level9);
category = (ImageView) findViewById(R.id.category_header);
category.setImageResource(R.drawable.header_figure);
}
}
public void setScoreHint(){
//************** get score from AppPreferences **************
AppPreferences AppPref = new AppPreferences(this);
int score = AppPref.getScore();
int hint = AppPref.getHintLeft();
//************** view score and hint in XML **************
TextView t1 = (TextView)findViewById(R.id.textValueHint);
TextView t2 = (TextView)findViewById(R.id.textValueScore);
t1.setTextSize(18);
t2.setTextSize(18);
t1.setText(Long.toString(hint));
t2.setText(Integer.toString(score));
}
public void setButton(){
//************** set question button **************
if ( flag1.equals("0")) {
buttonQuestion1.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion1.setText(question1);
} else {
buttonQuestion1.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion1.setText(answer1);
}
if ( flag2.equals("0")) {
buttonQuestion2.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion2.setText(question2);
} else {
buttonQuestion2.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion2.setText(answer2);}
if ( flag3.equals("0")) {
buttonQuestion3.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion3.setText(question3);
} else {
buttonQuestion3.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion3.setText(answer3);}
if ( flag4.equals("0")) {
buttonQuestion4.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion4.setText(question4);
} else {
buttonQuestion4.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion4.setText(answer4);}
if ( flag5.equals("0")) {
buttonQuestion5.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion5.setText(question5);
} else {
buttonQuestion5.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion5.setText(answer5);}
if ( flag6.equals("0")) {
buttonQuestion6.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion6.setText(question6);
} else {
buttonQuestion6.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion6.setText(answer6);}
if ( flag7.equals("0")) {
buttonQuestion7.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion7.setText(question7);
} else {
buttonQuestion7.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion7.setText(answer7);}
if ( flag8.equals("0")) {
buttonQuestion8.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion8.setText(question8);
} else {
buttonQuestion8.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion8.setText(answer8);}
if ( flag9.equals("0")) {
buttonQuestion9.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion9.setText(question9);
} else {
buttonQuestion9.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion9.setText(answer9);}
if ( flag10.equals("0")) {
buttonQuestion10.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion10.setText(question10);
} else {
buttonQuestion10.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion10.setText(answer10);}
if ( flag11.equals("0")) {
buttonQuestion11.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion11.setText(question11);
} else {
buttonQuestion11.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion11.setText(answer11);}
if ( flag12.equals("0")) {
buttonQuestion12.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion12.setText(question12);
} else {
buttonQuestion12.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion12.setText(answer12);}
if ( flag13.equals("0")) {
buttonQuestion13.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion13.setText(question13);
} else {
buttonQuestion13.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion13.setText(answer13);}
if ( flag14.equals("0")) {
buttonQuestion14.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion14.setText(question14);
} else {
buttonQuestion14.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion14.setText(answer14);}
if ( flag15.equals("0")) {
buttonQuestion15.setBackgroundResource(R.drawable.yellow_button);
buttonQuestion15.setText(question15);
} else {
buttonQuestion15.setBackgroundResource(R.drawable.buttonchecklist);
buttonQuestion15.setText(answer15);}
}
}
}
你应该在活动的暂停事件中清除值。
public void onPause() {
super.onPause();
getAnswer.clear();
getQuestion.clear()
}
你需要使用 .clear() 方式 ListView 以消除 listview 数据，在内部调用这个方法 onDestory() 办法
即
@Override
public void onDestroy() {
super.onDestroy();
getAnswer.clear();
getQuestion.clear()
// code of other listview which you want to clear
}
在下面的代码后面加上 onCreate 方法关闭。
@Override
public void onDestroy() {
super.onDestroy();
getAnswer.clear();
getQuestion.clear()
}
你需要调用 getAnswer.clear(); 清空该列表，同样，当您调用 finish() 的活动