小贝子编程

从SQLite创建一个以日期作为X轴的GraphView



我正在尝试从我的 sqlite 值创建一个图表，例如这里的日期与重量。稍后我将添加日期与脂肪等。但是这些应用程序被手机强制关闭 Logcat：

08-19 21:58:50.313 25858-25858/example.christopher.bd E/AndroidRuntime: FATAL EXCEPTION: main Process: example.christopher.bd, PID: 25858 java.lang.RuntimeException: Unable to start activity ComponentInfo{example.christopher.bd/example.christopher.bd.VIewGraph}: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference at com.jjoe64.graphview.series.DataPoint.(DataPoint.java:45) at example.christopher.bd.VIewGraph.onCreate(VIewGraph.java:48) at android.app.Activity.performCreate(Activity.java:7136) at android.app.Activity.performCreate(Activity.java:7127) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

显示图形的活动：

package example.christopher.bd;
import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import com.jjoe64.graphview.GraphView;
import com.jjoe64.graphview.helper.DateAsXAxisLabelFormatter;
import com.jjoe64.graphview.series.DataPoint;
import com.jjoe64.graphview.series.LineGraphSeries;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class VIewGraph extends AppCompatActivity {
LineGraphSeries<DataPoint> series;
DatabaseHelper mDatabaseHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view_graph);
mDatabaseHelper = new DatabaseHelper(this);
String y;
Float z;
Date d1;
Cursor data = mDatabaseHelper.readEntry();
int rows = data.getCount();
data.moveToFirst();
GraphView graph = (GraphView) findViewById(R.id.graph11);
series = new LineGraphSeries<DataPoint>();
for(int i = 0;  i <rows; i++){
data.moveToNext();
String x = data.getString(2);
y = data.getString(3);
z = Float.parseFloat(y);
Date date1 = null;
try {
date1 = new SimpleDateFormat("dd/MM/yyyy").parse(x);
} catch (Exception e) {
e.printStackTrace();
}
series.appendData(new DataPoint(date1, z), true, 25);
}
graph.addSeries(series);
graph.getGridLabelRenderer().setNumHorizontalLabels(3);
graph.getGridLabelRenderer().setHumanRounding(false);
}
}

这是数据库助手的代码

package example.christopher.bd;

import android.app.DatePickerDialog;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.icu.util.Calendar;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

public class DatabaseHelper extends SQLiteOpenHelper{
private static final String TAG = "DatabaseHelper";
private static final String TABLE_NAME = "BodyData";
private static final String COL1 = "ID";
private static final String COL2 = "tdate";
private static final String COL2a = "ttime";
private static final String COL3 = "weight";
private static final String COL4 = "fat";
private static final String COL5 = "hydration";
private static final String COL6 = "muscle";
private static final String COL7 = "bone";
//private static final String COL8 = "time";
private TextView mDisplayDate;
private DatePickerDialog.OnDateSetListener mDateSetListener;
public DatabaseHelper(Context context) {
super(context, TABLE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createTable = " CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, tdate string, ttime string, weight float, fat float, hydration float, muscle float, bone float)";
//String createTable = " CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, tday integer, tmonth integer, tyear integer, weight float, fat float, hydration float, muscle float, bone float)";
db.execSQL(createTable);
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
db.execSQL(" DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public boolean addData(String tdate, String ttime, String weight, String fat, String hydration, String muscle, String bone) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL2, tdate);
contentValues.put(COL2a, ttime);
contentValues.put(COL3, weight);
contentValues.put(COL4, fat);
contentValues.put(COL5, hydration);
contentValues.put(COL6, muscle);
contentValues.put(COL7, bone);
//contentValues.put(COL8, time);
long result = db.insert(TABLE_NAME,null ,contentValues);
if(result == -1)
return false;
else
return true;
}
public Cursor getData(){
SQLiteDatabase db = this.getWritableDatabase();
String query = "SELECT * FROM " + TABLE_NAME;
Cursor data = db.rawQuery(query, null);
return data;
}
public void deleteAll()
{
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME,null,null);
db.execSQL("delete from "+ TABLE_NAME);
db.close();
}
public Cursor readEntry(){
SQLiteDatabase db = this.getWritableDatabase();
String[] allColumns = new String[]{
DatabaseHelper.COL1,
DatabaseHelper.COL2,
DatabaseHelper.COL2a,
DatabaseHelper.COL3,
DatabaseHelper.COL4,
DatabaseHelper.COL5,
DatabaseHelper.COL6,
DatabaseHelper.COL7,
};
Cursor c = db.query(DatabaseHelper.TABLE_NAME, allColumns, null, null, null, null, null);
if (c != null) {
c.moveToFirst();
}
return c;
}
}

记录数据的活动(日期、重量等(

package example.christopher.bd;
import android.app.DatePickerDialog;
import android.app.TimePickerDialog;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.icu.util.Calendar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TimePicker;
import android.widget.Toast;
public class Logging extends AppCompatActivity {
private static final String TAG = "Logging";
DatabaseHelper mDatabaseHelper;
EditText editWeight, editFat, editHydration, editMuscle, editBone, editTime, editASD;
private Button button2;
private TextView mDisplayDate, mDisplayTime;
private DatePickerDialog.OnDateSetListener mDateSetListener;
private TimePickerDialog.OnTimeSetListener mTimeSetListener;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_logging);
button2 = (Button) findViewById(R.id.button2);
mDisplayDate = (TextView) findViewById(R.id.tvDate);
mDatabaseHelper = new DatabaseHelper(this);
mDisplayTime = (TextView) findViewById(R.id.tvTime);
editWeight = (EditText) findViewById(R.id.editWeight);
editFat = (EditText) findViewById(R.id.editFat);
editHydration = (EditText) findViewById(R.id.editHydration);
editMuscle = (EditText) findViewById(R.id.editMuscle);
editBone = (EditText) findViewById(R.id.editBone);
mDisplayDate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Calendar cal = Calendar.getInstance();
int year = cal.get(Calendar.YEAR);
int month = cal.get(Calendar.MONTH);
int day = cal.get(Calendar.DAY_OF_MONTH);
DatePickerDialog dialog = new DatePickerDialog(
Logging.this,
android.R.style.Theme_Holo_Light_Dialog_MinWidth,
mDateSetListener,
year,month,day);
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
dialog.show();
}
});
mDateSetListener = new DatePickerDialog.OnDateSetListener() {
@Override
public void onDateSet(DatePicker datePicker, int year, int month, int day) {
month = month + 1;
Log.d(TAG, "onDateSet: mm/dd/yyyy: " + day + "/" + month + "/" + year);
String date = day + "/" + month + "/" + year;
mDisplayDate.setText(date);
}
};
mDisplayTime.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Calendar mTime = Calendar.getInstance();
int mHour = mTime.get(Calendar.HOUR_OF_DAY);
int mMinute = mTime.get(Calendar.MINUTE);
TimePickerDialog timePickerDialog = new TimePickerDialog(Logging.this,
new TimePickerDialog.OnTimeSetListener() {
@Override
public void onTimeSet(TimePicker view, int hourOfDay,
        int minute) {
mDisplayTime.setText(hourOfDay + ":" + minute);
}
}, mHour, mMinute, true);
timePickerDialog.show();
}
});
LogData();
}
public void LogData(){
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
boolean isInserted = mDatabaseHelper.addData(
mDisplayDate.getText().toString(),
mDisplayTime.getText().toString(),
editWeight.getText().toString(),
editFat.getText().toString(),
editHydration.getText().toString(),
editMuscle.getText().toString(),
editBone.getText().toString()
);
if (isInserted == true)
Toast.makeText(Logging.this, "Data Inserted", Toast.LENGTH_LONG).show();
else
Toast.makeText(Logging.this, "Data not Inserted", Toast.LENGTH_LONG).show();
}
});
}

}

谁能帮我？

java.lang.NullPointerException： Try to invoke virtual method 'long java.util.Date.getTime((' on a null object reference

表示您正在调用/正在使用的代码正在null的Date对象上调用getTime()。

更详细

尝试在 空对象引用位于 com.jjoe64.graphview.series.DataPoint.(数据点.java：45( 在 example.christopher.bd.VIewGraph.onCreate(VIewGraph.java：48(

表示这是在第 48 行的VIewGraph.java中启动的。

就在上面有一个try-catch块可以捕获解析日期时的问题，但您最终不会检查Date对象是否为非 null。任何错误都会被忽略。然后，将此空Date对象提供给seriesinseries.appendData(new DataPoint(date1, z), true, 25);

一个快速的解决方法是改变

try {
date1 = new SimpleDateFormat("dd/MM/yyyy").parse(x);
} catch (Exception e) {
e.printStackTrace();
}
series.appendData(new DataPoint(date1, z), true, 25);

..自。。。

try {
date1 = new SimpleDateFormat("dd/MM/yyyy").parse(x);
series.appendData(new DataPoint(date1, z), true, 25);
} catch (Exception e) {
e.printStackTrace();
}

看起来您已经对表的列进行了更改(COL2a而不是COL8(
如果是这种情况，您是否从测试它的设备/模拟器中卸载了该应用程序？
如果没有，你必须。
每次在类onCreate()进行更改时，表架构都不会更改DatabaseHelper。 当数据库不存在时执行onCreate()。
现在一个逻辑问题：
在活动的 onCreate(( 中，你执行：

data.moveToFirst();

因此，光标数据指向其第一行。
然后在 for 循环的第一行中执行：

data.moveToNext();

因此，光标数据指向其第二行(如果有第二行(。
所以你肯定会错过第一行的数据。
但是由于迭代次数与行数相等，因此最后一次迭代将获取空数据！
建议移动data.moveToNext();作为for循环的最后一个语句。

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