公式：总距离行程（当前里程表-以前的里程表）/编号升汽油泵
我已经在代码中完成了此公式，但是我的代码并未完全完成。
我的代码是（当前里程表/汽油数量）。
我想减去以前的里程表，但是我不知道该怎么做。
我将根据日期将信息存储在数据库中。
有人可以指导我怎么做吗？
为了获得总距离行驶的公式（当前里程表-以前的里程表）/升汽油泵..
这是我的代码：
我知道我的String lastOdm =“”出了问题； ，但不确定如何解决该错误。
日志猫：
01-22 11:01:12.136: E/AndroidRuntime(7078): FATAL EXCEPTION: main
01-22 11:01:12.136: E/AndroidRuntime(7078): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fuellog/com.example.fuellog.MainActivity}: java.lang.NullPointerException
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.os.Handler.dispatchMessage(Handler.java:99)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.os.Looper.loop(Looper.java:137)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread.main(ActivityThread.java:5041)
01-22 11:01:12.136: E/AndroidRuntime(7078): at java.lang.reflect.Method.invokeNative(Native Method)
01-22 11:01:12.136: E/AndroidRuntime(7078): at java.lang.reflect.Method.invoke(Method.java:511)
01-22 11:01:12.136: E/AndroidRuntime(7078): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-22 11:01:12.136: E/AndroidRuntime(7078): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-22 11:01:12.136: E/AndroidRuntime(7078): at dalvik.system.NativeStart.main(Native Method)
01-22 11:01:12.136: E/AndroidRuntime(7078): Caused by: java.lang.NullPointerException
01-22 11:01:12.136: E/AndroidRuntime(7078): at com.example.fuellog.DBAdapter.getLastOdometer(DBAdapter.java:104)
01-22 11:01:12.136: E/AndroidRuntime(7078): at com.example.fuellog.MainActivity.onCreate(MainActivity.java:74)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.Activity.performCreate(Activity.java:5104)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-22 11:01:12.136: E/AndroidRuntime(7078): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-22 11:01:12.136: E/AndroidRuntime(7078): ... 11 more
mainactivity.java
public class MainActivity extends Activity {
// TableLayout tablelayout_Log = null;
Button saveButton = null;
Button cancelButton = null;
// Button searchButton = null;
static EditText dateEdit;
EditText priceEdit;
EditText pumpEdit;
TextView costView;
EditText odometerEdit;
TextView fconView;
TextWatcher textWatcher;
String priceEditStr ="",pumpEditStr="";
String odmEditStr = "";
String lastOdm = "";
double result;
double resultCon;
private int mYear;
private int mMonth;
private int mDay;
static final int DATE_DIALOG_ID = 0;
public boolean isNumeric(String str)
{
return str.matches("-?\\d+(\\.\\d+)?");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
costView = (TextView)findViewById(R.id.tcost);
dateEdit = (EditText)findViewById(R.id.date);
priceEdit = (EditText)findViewById(R.id.fuelprice);
pumpEdit = (EditText)findViewById(R.id.fuelpump);
odometerEdit = (EditText)findViewById(R.id.odometer);
fconView = (TextView)findViewById(R.id.fcon);
dateEdit.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// showDialog(DATE_DIALOG_ID);
DialogFragment newFragment = new DatePickerFragment();
newFragment.show(getFragmentManager(), "datePicker");
}
});
priceEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !priceEdit.getText().toString().trim().equalsIgnoreCase(null))
priceEditStr = priceEdit.getText().toString().trim();
if(!pumpEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(null))
pumpEditStr = pumpEdit.getText().toString().trim();
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
{
result = Double.parseDouble(priceEditStr) * Double.parseDouble(pumpEditStr);
costView.setText(" "+result);
}
}
});
pumpEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!priceEdit.getText().toString().trim().equalsIgnoreCase(""))
priceEditStr = priceEdit.getText().toString().trim();
if(!pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
pumpEditStr = pumpEdit.getText().toString().trim();
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
{
result = Double.parseDouble(priceEditStr) * Double.parseDouble(pumpEditStr);
costView.setText(" "+result);
}
}
});
odometerEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!odometerEdit.getText().toString().trim().equalsIgnoreCase(""))
odmEditStr = odometerEdit.getText().toString().trim();
if(!odometerEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase("") && !lastOdm.trim().equalsIgnoreCase(null) && !lastOdm.trim().equalsIgnoreCase(" "))
{
DBAdapter dbAdaptor = new DBAdapter(getApplicationContext());
lastOdm = dbAdaptor.getLastOdometer();
resultCon = Double.parseDouble(odmEditStr) - Double.parseDouble(lastOdm) / Double.parseDouble(pumpEditStr);
fconView.setText(" "+resultCon);
}
}
});
cancelButton = (Button) findViewById(R.id.cancelBTN);
cancelButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
/// Create Intent for About and start activity
Intent summaryView=new Intent(getApplicationContext(),summary.class);
startActivity(summaryView);
}
});
//Insert
saveButton = (Button) findViewById(R.id.saveBTN);
saveButton.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
DBAdapter dbAdaptor = new DBAdapter(getApplicationContext());
try
{
dbAdaptor.open();
// String cursor = dbAdaptor.getLastOdometer();
String date = dateEdit.getText().toString();
String price = priceEdit.getText().toString();
String pump = pumpEdit.getText().toString();
String tcost = costView.getText().toString();
String odometer = odometerEdit.getText().toString();
String fcon = fconView.getText().toString();
dbAdaptor.insertLog(date, price, pump, tcost, odometer, fcon);
Intent summaryView=new Intent(getApplicationContext(),summary.class);
startActivity(summaryView);
}
catch(Exception e){
Log.d("Fuel Log", e.getMessage());
}
finally
{
if(dbAdaptor != null)
dbAdaptor.close();
}
}
});
}
public static class DatePickerFragment extends DialogFragment
implements DatePickerDialog.OnDateSetListener {
public EditText editText;
DatePicker dpResult;
public Dialog onCreateDialog(Bundle savedInstanceState) {
// Use the current date as the default date in the picker
final Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
//return new DatePickerDialog(getActivity(), (EditSessionActivity)getActivity(), year, month, day);
// Create a new instance of DatePickerDialog and return it
return new DatePickerDialog(getActivity(), this, year, month, day);
}
public void onDateSet(DatePicker view, int year, int month, int day) {
dateEdit.setText(String.valueOf(day) + "/"
+ String.valueOf(month + 1) + "/" + String.valueOf(year));
// set selected date into datepicker also
}
}
}
dbadapter.java
public class DBAdapter {
public static final String KEY_ROWID = "_id";
public static final String KEY_DATE = "date";
public static final String KEY_PRICE = "fuelprice";
public static final String KEY_FUEL = "fuelpump";
public static final String KEY_COST = "tcost";
public static final String KEY_ODM = "odometer";
public static final String KEY_CON = "fcon";
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "MyDB";
private static final String DATABASE_TABLE = "fuelLog";
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_CREATE =
"create table fuelLog (_id integer primary key autoincrement, " + "date text not null, fuelprice text not null, fuelpump text not null, tcost text not null, odometer text not null, fcon text not null);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx){
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db)
{
try{
db.execSQL(DATABASE_CREATE);
}catch (SQLException e){
e.printStackTrace();
}
}//onCreate
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS contacts");
onCreate(db);
}//onUpgrade
}//DatabaseHelper
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}//open
//---closes the database---
public void close()
{
DBHelper.close();
}//close
//---insert a log into the database---
public long insertLog(String date, String fuelprice, String fuelpump,String tcost,String odometer,String fcon )
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_DATE, date);
initialValues.put(KEY_PRICE, fuelprice);
initialValues.put(KEY_FUEL, fuelpump);
initialValues.put(KEY_COST, tcost);
initialValues.put(KEY_ODM, odometer);
initialValues.put(KEY_CON, fcon);
return db.insert(DATABASE_TABLE, null, initialValues);
}//insertLog
public String getLastOdometer() {
Cursor cursor = db.query(DATABASE_TABLE, new String[] {KEY_ODM}, "KEY_ROWID=(SELECT MAX(KEY_ROWID) FROM " + DATABASE_TABLE + ")", null, null, null, null);
try {
if(cursor.moveToNext()) {
return cursor.getString(0);
} else {
return null;
}
} finally {
cursor.close();
}
}
}
最佳答案
最终编辑答案
看到解决
import java.util.Calendar;
import android.os.Bundle;
import android.app.Activity;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.app.DialogFragment;
import android.content.Intent;
import android.content.SharedPreferences;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class EditResult1 extends Activity {
// TableLayout tablelayout_Log = null;
Button saveButton = null;
Button cancelButton = null;
// Button searchButton = null;
static EditText dateEdit;
EditText priceEdit;
EditText pumpEdit;
TextView costView;
EditText odometerEdit;
TextView fconView;
TextWatcher textWatcher;
String priceEditStr ="",pumpEditStr="";
String odmEditStr = "";
String lastOdm = "";
double result;
double resultCon;
private int mYear;
private int mMonth;
private int mDay;
SharedPreferences sp;
static final int DATE_DIALOG_ID = 0;
public boolean isNumeric(String str)
{
return str.matches("-?\\d+(\\.\\d+)?");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.edit_sample);
costView = (TextView)findViewById(R.id.tcost);
dateEdit = (EditText)findViewById(R.id.date);
priceEdit = (EditText)findViewById(R.id.fuelprice);
pumpEdit = (EditText)findViewById(R.id.fuelpump);
odometerEdit = (EditText)findViewById(R.id.odometer);
fconView = (TextView)findViewById(R.id.fcon);
/**
* Shared preference
**/
sp=this.getSharedPreferences("result_store", MODE_WORLD_READABLE);
lastOdm=sp.getString("ODO", lastOdm);
if(lastOdm.trim().equalsIgnoreCase("NA"))
Toast.makeText(getApplicationContext(), " "+lastOdm.trim(), Toast.LENGTH_LONG).show();
else
Toast.makeText(getApplicationContext(), " "+lastOdm.trim(), Toast.LENGTH_LONG).show();
dateEdit.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// showDialog(DATE_DIALOG_ID);
DialogFragment newFragment = new DatePickerFragment();
newFragment.show(getFragmentManager(), "datePicker");
}
});
priceEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !priceEdit.getText().toString().trim().equalsIgnoreCase(null))
priceEditStr = priceEdit.getText().toString().trim();
if(!pumpEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(null))
pumpEditStr = pumpEdit.getText().toString().trim();
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
{
result = Double.parseDouble(priceEditStr) * Double.parseDouble(pumpEditStr);
costView.setText(" "+result);
}
}
});
pumpEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!priceEdit.getText().toString().trim().equalsIgnoreCase(""))
priceEditStr = priceEdit.getText().toString().trim();
if(!pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
pumpEditStr = pumpEdit.getText().toString().trim();
if(!priceEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase(""))
{
result = Double.parseDouble(priceEditStr) * Double.parseDouble(pumpEditStr);
costView.setText(" "+result);
}
}
});
odometerEdit.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void afterTextChanged(Editable editable) {
//here, after we introduced something in the EditText we get the string from it
if(!odometerEdit.getText().toString().trim().equalsIgnoreCase(""))
odmEditStr = odometerEdit.getText().toString().trim();
if(!odometerEdit.getText().toString().trim().equalsIgnoreCase("") && !pumpEdit.getText().toString().trim().equalsIgnoreCase("") && !lastOdm.trim().equalsIgnoreCase("") && !lastOdm.trim().equalsIgnoreCase("NA"))
{
resultCon = Double.parseDouble(odmEditStr) - Double.parseDouble(lastOdm) / Double.parseDouble(pumpEditStr);
fconView.setText(" "+resultCon);
}
}
});
cancelButton = (Button) findViewById(R.id.cancelBTN);
cancelButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
/// Create Intent for About and start activity
Intent summaryView=new Intent(getApplicationContext(),ActivityA.class);
startActivity(summaryView);
}
});
//Insert
saveButton = (Button) findViewById(R.id.saveBTN);
saveButton.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
DBAdapter dbAdaptor = new DBAdapter(getApplicationContext());
try
{
dbAdaptor.open();
// String cursor = dbAdaptor.getLastOdometer();
String date = dateEdit.getText().toString();
String price = priceEdit.getText().toString();
String pump = pumpEdit.getText().toString();
String tcost = costView.getText().toString();
String odometer = odometerEdit.getText().toString();
String fcon = fconView.getText().toString();
if(!odometer.trim().equalsIgnoreCase(""))
{
SharedPreferences.Editor editor=sp.edit();
editor.putString("ODO", odometer.trim());
editor.commit();
}
else
{
SharedPreferences.Editor editor=sp.edit();
editor.putString("ODO", "NA");
editor.commit();
}
dbAdaptor.insertLog(date, price, pump, tcost, odometer, fcon);
Intent summaryView=new Intent(getApplicationContext(),ActivityA.class);
startActivity(summaryView);
}
catch(Exception e){
Log.d("Fuel Log", e.getMessage());
}
finally
{
if(dbAdaptor != null)
dbAdaptor.close();
}
}
});
}
public static class DatePickerFragment extends DialogFragment
implements DatePickerDialog.OnDateSetListener {
public EditText editText;
DatePicker dpResult;
public Dialog onCreateDialog(Bundle savedInstanceState) {
// Use the current date as the default date in the picker
final Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
//return new DatePickerDialog(getActivity(), (EditSessionActivity)getActivity(), year, month, day);
// Create a new instance of DatePickerDialog and return it
return new DatePickerDialog(getActivity(), this, year, month, day);
}
public void onDateSet(DatePicker view, int year, int month, int day) {
dateEdit.setText(String.valueOf(day) + "/"
+ String.valueOf(month + 1) + "/" + String.valueOf(year));
// set selected date into datepicker also
}
}
}
将EditResult1替换为您的类名，对于XML也应相同。
关于java - 如何减去先前的键值(存储在数据库中)，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/21236793/