所以我创建了一个有3个编辑文本的应用程序，用户必须先输入值，然后点击＆＃34;查看记录＆＃34;显示添加到SQLite数据库中的记录的列表视图。添加记录是有效的，我能够将数据存储到数据库中，但是我无法显示它们，因为每当我按下＆＃34;查看记录＆＃34;它就会一直崩溃。 。附件是我的ViewRecords页面的代码以及databasehelper。请指教。感谢。
ViewRecords.java
package mdad.project;
import java.util.ArrayList;
import com.example.manandhowproject.R;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class ViewRecords extends Activity {
DatabaseHelper dbhelper;
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewrecords);
dbhelper = new DatabaseHelper(this);
populateListView();
}
private void populateListView()
{
Cursor records = dbhelper.getRecords();
ArrayList<String> listRec = new ArrayList<String>();
while(records.moveToNext()){
listRec.add(records.getString(1));
}
ListAdapter adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,listRec);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
String BTemp = adapterView.getItemAtPosition(i).toString();
String HRate = adapterView.getItemAtPosition(i).toString();
String Bmi = adapterView.getItemAtPosition(i).toString();
Cursor data = dbhelper.getRecID(BTemp, HRate, Bmi);
int recID = -1;
while(data.moveToNext()){
recID = data.getInt(0);
}
if(recID > -1){
Intent editScreenIntent = new Intent(ViewRecords.this, EditDel.class);
editScreenIntent.putExtra("id",recID);
editScreenIntent.putExtra("Body Temperature",BTemp);
editScreenIntent.putExtra("Heart Rate",HRate);
editScreenIntent.putExtra("BMI",Bmi);
startActivity(editScreenIntent);
}
else{
Toast.makeText(getApplicationContext(), "No ID Associated", Toast.LENGTH_LONG).show();
}
}
});
}}
DatabaseHelper.java
package mdad.project;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "medrec.db";
public static final String TABLE_NAME = "myrec_data";
public static final String COL1 = "ID";
public static final String COL2 = "BodyTemp";
public static final String COL3 = "HeartRate";
public static final String COL4 = "BMI";
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, " + COL2 + " TEXT, " + COL3 + " TEXT, " + COL4 + " TEXT);";
db.execSQL(createTable);
}
@Override
public void onUpgrade (SQLiteDatabase db,int i, int i1)
{
db.execSQL("DROP IF TABLE EXISTS " + TABLE_NAME);
onCreate(db);
}
public boolean addRecord(String BodyTemp, String HeartRate, String BMI) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL2, BodyTemp);
contentValues.put(COL3, HeartRate);
contentValues.put(COL4, BMI);
long result = db.insert(TABLE_NAME, null, contentValues);
if (result == -1) {
return false;
} else {
return true;
}
}
public Cursor getRecords()
{
SQLiteDatabase db = this.getWritableDatabase();
String query = "SELECT * FROM " + TABLE_NAME;
Cursor records = db.rawQuery(query, null);
return records;
}
public Cursor getRecID(String BTemp, String Hrate, String Bmi){
SQLiteDatabase db = this.getWritableDatabase();
String query = "SELECT " + COL1 + " FROM " + TABLE_NAME +
" WHERE " + COL2 + " = '" + BTemp + "AND" + COL3 + " = '" + Hrate + "AND" + COL4 + " = '" + Bmi +"'";
Cursor data = db.rawQuery(query, null);
return data;
}
public void updateBtemp(String bodytemp, int selectedID,
String selectedBtemp) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "UPDATE " + TABLE_NAME + " SET " + COL2 +
" = '" + bodytemp + "' WHERE " + COL1 + " = '" + selectedID + "'" +
" AND " + COL2 + " = '" + selectedBtemp + "'";
db.execSQL(query);
}
public void updateHrate(String heartrate, int selectedID,
String selectedHrate) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "UPDATE " + TABLE_NAME + " SET " + COL3 +
" = '" + heartrate + "' WHERE " + COL1 + " = '" + selectedID + "'" +
" AND " + COL3 + " = '" + selectedHrate + "'";
db.execSQL(query);
}
public void updateBMI(String bmi, int selectedID, String selectedBMI) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "UPDATE " + TABLE_NAME + " SET " + COL4 +
" = '" + bmi + "' WHERE " + COL1 + " = '" + selectedID + "'" +
" AND " + COL4 + " = '" + selectedBMI + "'";
db.execSQL(query);
}
public void deleteBtemp(int selectedID, String selectedBtemp) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "DELETE FROM " + TABLE_NAME + " WHERE "
+ COL1 + " = '" + selectedID + "'" +
" AND " + COL2 + " = '" + selectedBtemp + "'";
db.execSQL(query);
}
public void deleteHrate(int selectedID, String selectedHrate) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "DELETE FROM " + TABLE_NAME + " WHERE "
+ COL1 + " = '" + selectedID + "'" +
" AND " + COL3 + " = '" + selectedHrate + "'";
db.execSQL(query);
}
public void deleteBMI(int selectedID, String selectedBMI) {
SQLiteDatabase db = this.getWritableDatabase();
String query = "DELETE FROM " + TABLE_NAME + " WHERE "
+ COL1 + " = '" + selectedID + "'" +
" AND " + COL4 + " = '" + selectedBMI + "'";
db.execSQL(query);
}
}
崩溃日志
02-07 00:33:27.041: E/AndroidRuntime(884): FATAL EXCEPTION: main
02-07 00:33:27.041: E/AndroidRuntime(884): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.manandhowproject/mdad.project.ViewRecords}: java.lang.NullPointerException
02-07 00:33:27.041: E/AndroidRuntime(884): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
02-07 00:55:30.310: E/AndroidRuntime(10059): FATAL EXCEPTION: main
02-07 00:55:30.310: E/AndroidRuntime(10059): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.manandhowproject/mdad.project.ViewRecords}: java.lang.NullPointerException
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.os.Handler.dispatchMessage(Handler.java:99)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.os.Looper.loop(Looper.java:137)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread.main(ActivityThread.java:5103)
02-07 00:55:30.310: E/AndroidRuntime(10059): at java.lang.reflect.Method.invokeNative(Native Method)
02-07 00:55:30.310: E/AndroidRuntime(10059): at java.lang.reflect.Method.invoke(Method.java:525)
02-07 00:55:30.310: E/AndroidRuntime(10059): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
02-07 00:55:30.310: E/AndroidRuntime(10059): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
02-07 00:55:30.310: E/AndroidRuntime(10059): at dalvik.system.NativeStart.main(Native Method)
02-07 00:55:30.310: E/AndroidRuntime(10059): Caused by: java.lang.NullPointerException
02-07 00:55:30.310: E/AndroidRuntime(10059): at mdad.project.ViewRecords.populateListView(ViewRecords.java:37)
02-07 00:55:30.310: E/AndroidRuntime(10059): at mdad.project.ViewRecords.onCreate(ViewRecords.java:26)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.Activity.performCreate(Activity.java:5133)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-07 00:55:30.310: E/AndroidRuntime(10059): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
02-07 00:55:30.310: E/AndroidRuntime(10059): ... 11 more
答案 0 :(得分：2)
从“创建它”中的本地方法中删除ListView的声明，将其初始化以供本地使用。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.viewrecords);
// ListView listView = (ListView) findViewById(R.id.listView);
listView = (ListView) findViewById(R.id.listView);
dbhelper = new DatabaseHelper(this);
populateListView();
}
答案 1 :(得分：1)
你有两个listView变量，一个被定义为一个类变量，另一个是本地的，只有onCreate方法的范围。
调用populateListView方法时，它使用的类变量listView为空。
修复方法是确保您始终使用班级listView。
因此改变： -
ListView listView = (ListView) findViewById(R.id.listView);
到
listView = (ListView) findViewById(R.id.listView);