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你好我正在編程一個Android應用程序，它有一個數據庫，允許用戶搜索特定事件。目前，我正在遇到活動入門的問題。我在我的Droid Bionic設備上測試這個應用程序，並使用eclipse SDK 4.2進行編程。我如何開始我的活動？我對android很陌生，我學到的所有東西都是通過我在網上教我自己和其他教程的。任何幫助將不勝感激。Android應用程序無法啓動活動
主要活動其中創建分貝：
package com.example.database;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.widget.EditText;
public class MainActivity
{
EditText dEdit;
public static final String KEY_ROWID = "_id";
public static final String KEY_BUSINESS = "business";
public static final String KEY_ADDRESS = "address";
public static final String KEY_PHONE = "phone";
public static final String KEY_HOURS = "hours";
public static final String KEY_WEB = "website";
public static final String KEY_TYPE = "type";
private static final String TAG = "MainActivity";
private static final String DATABASE_NAME = "LocalDB";
private static final String DATABASE_TABLE = "Business";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
"create table Business (_id integer primary key autoincrement, "
+ "business text not null, address text not null, phone text not null,hours text not null,website text not null,type text not null"
+ ")";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase mDB;
public MainActivity(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
try{
mDB=db;
mDB.execSQL(DATABASE_CREATE);
} catch(SQLException e){
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
try{
mDB=db;
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
mDB.execSQL("DROP TABLE IF EXISTS Business");
onCreate(mDB);
}catch (SQLException e){
e.printStackTrace();
}
}
}
//---opens the database---
public MainActivity open() throws SQLException
{
mDB = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a title into the database---
public long insertTitle(String business, String address, String phone, String hours, String website, String type)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_BUSINESS, business);
initialValues.put(KEY_ADDRESS, address);
initialValues.put(KEY_PHONE, phone);
initialValues.put(KEY_HOURS, hours);
initialValues.put(KEY_WEB, hours);
initialValues.put(KEY_TYPE, type);
return mDB.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular title---
public boolean deleteTitle(long rowId)
{
return mDB.delete(DATABASE_TABLE, KEY_ROWID +
"=" + rowId, null) > 0;
}
//---retrieves all the titles---
public Cursor getAllTitles()
{
return mDB.query(DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_BUSINESS,
KEY_ADDRESS,
KEY_PHONE,
KEY_HOURS,
KEY_WEB,
KEY_TYPE},
null,
null,
null,
null,
null);
}
//---retrieves a particular title---
public Cursor getTitle(long rowId) throws SQLException
{
Cursor mCursor =
mDB.query(true, DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_BUSINESS,
KEY_ADDRESS,
KEY_PHONE,
KEY_HOURS,
KEY_WEB,
KEY_TYPE
},
KEY_ROWID + "=" + rowId,
null,
null,
null,
null,
null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a title---
public boolean updateTitle(long rowId, String business,
String address, String phone, String hours, String website, String type)
{
ContentValues args = new ContentValues();
args.put(KEY_BUSINESS, business);
args.put(KEY_ADDRESS, address);
args.put(KEY_PHONE, phone);
args.put(KEY_HOURS,hours);
args.put(KEY_WEB,website);
args.put(KEY_TYPE, type);
return mDB.update(DATABASE_TABLE, args,
KEY_ROWID + "=" + rowId, null) > 0;
}
}
數據添加到DB：
package com.example.database;
import android.app.Activity;
import android.os.Bundle;
public class DBActivity extends Activity {
//MainActivity eventsData;
//EditText output;
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MainActivity db= new MainActivity(this);
//output = (EditText) findViewById(R.id.textView1);
//type.setOnClickListener(
// new OnClickListener(){
// public void onClick(View view){
// Log.v("Entry",dEdit.getText().toString());
// }
/// });
//try{String destPath="/data/data" +getPackageName()+ "/databases/BloomBusiness";
// File f = new File(destPath);
// if(!f.exists()){
// CopyDB(getBaseContext().getAssets().open("db"), new FileOutputStream(destPath));
// }
//
//
//}catch(FileNotFoundException e){
// e.printStackTrace();
//}catch(IOException e){
// e.printStackTrace();
//}
db.open();
//inserting all data
long id;
id =db.insertTitle("BloomingFoods","419 E. Kirkwood Ave. Bloomington, IN", "812-336-5300", "M-Sat:8AM-9PM Sun:9AM-8PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("BloomingFoods","316 W. 6th Street Bloomington, IN", "812-333-5300", "M-Sat:7AM-10PM Sun:9AM-9PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("BloomingFoods","3220 E. 3rd Street Bloomington, IN", "812-336-5300", "M-Sun:8AM-10PM","http://www.bloomingfoods.coop","Grocery");
id=db.insertTitle("The Uptown Cafe","102 E. Kirkwood Ave. Bloomington, IN", "812-339-0900", "M-Sat:8AM-9PM Sun:9AM-8PM", "http://www.the-uptown.com/","Cajun-Creole");
id=db.insertTitle("Crazy Horse","214 W. Kirkwood Ave. Bloomington, IN", "812-336-8877", "M-Sat:11AM-2AM Sun:Noon-Midnight", "http://www.crazyhorseindiana.com/","Restaurant & Live Music");
id=db.insertTitle("FARMbloomington","108 E. Kirkwood Ave. Bloomington, IN", "812-323-0002", "Tue.-Thurs.:8AM-10PM F:8AM-1AM Sat: 10AM-3AM Sun: 10AM-10PM","http://www.farm-bloomington.com","Grocery");
id=db.insertTitle("Laughing Planet","322 E. Kirkwood Ave. Bloomington, IN", "812-323-2233", "M-Sun:11AM-9PM","http://www.facebook.com/laughingplanetbtown","Burritos & Salads");
id=db.insertTitle("Soma Coffeehouse","322 E. Kirkwood Bloomington, IN", "812-331-2770", "M-Sat:7AM-11PM Sun:8AM-11PM","http://www.iheartsoma.com","Coffee House");
id=db.insertTitle("Upland Brewing Company","350 W. 11th St. Bloomington, IN", "812-336-2337", "M-Thurs:11AM-Midnight F-Sat:11AM-1AM Sun: Noon-Midnight","http://www.uplandbeer.com","Brewery & Restaraunt");
id=db.insertTitle("Nick's English Hut","423 E. Kirkwood Bloomington, IN", "812-332-4040", "M-Sat:11AM-2AM Sun: Noon-Midnight","http://www.nicksenglishhut.com","Bar & Restaraunt");
id=db.insertTitle("The Village Deli","409 E. Kirkwood Ave. Bloomington, IN", "812-336-2303", "M-F:7AM-8PM Sat-Sun 8AM-8PM","http://www.villagedeli.biz","Breakfast,Lunch,Dinner");
id=db.insertTitle("Rachael's Cafe","300 E. 3rd St. Bloomington, IN", "812-330-1882", "M-F:8AM-9PM Sat-Sun 9AM-9PM","http://www.rachaelscafe.com","Coffee House & Live Music");
id=db.insertTitle("Happy Pig","1604 W. 7th St. Bloomington, IN", "None", "W:Sample Gates Noon-3PM Thurs:Sample Gates Noon-3PM F:Atlas Bar 11:30PM-3:30AM Sat:Courthouse Square 11:30PM-3:30AM","http://www.happypigbloomington.com","BBQ Streetfood");
id=db.insertTitle("Lennie's Restaurant and Brewpub","1795 E. 10th St. Bloomington, IN", "812-323-2112", "Sun-Th:11AM-11PM F-Sat 11AM-Midnight","http://www.lenniesgourmetpizza.com","Bar & Restaurant");
id=db.insertTitle("Pizza X","1791 E. 10th St. Bloomington, IN", "812-339-7737", "Sun-Tues:11AM-2AM Wed-Thur: 11AM-3AM F-Sat:11AM-4AM","http://www.pizzaxbloomington.com","Pizza");
id=db.insertTitle("Pizza X","1610 W. 3rd St. Bloomington, IN", "812-332-2522", "Sun-Wed:4PM-Midnight Thur: 4PM-3AM F-Sat:4PM-4AM","http://www.pizzaxbloomington.com","Pizza");
id=db.insertTitle("Pizza X","877 S. College Mall Rd. Bloomington, IN", "812-355-5000", "Sun-Wed:4PM-Midnight Thur: 4PM-3AM F-Sat:4PM-4AM","http://www.pizzaxbloomington.com","Pizza");
}
在搜索的DB：
package com.example.database;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class DBUse extends Activity {
EditText dEdit;
SQLiteDatabase data;
public static final String KEY_ROWID = "_id";
public static final String KEY_BUSINESS = "business";
public static final String KEY_ADDRESS = "address";
public static final String KEY_PHONE = "phone";
public static final String KEY_HOURS = "hours";
public static final String KEY_WEB = "website";
public static final String KEY_TYPE = "type";
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MainActivity datab = new MainActivity(this);
Button buttonName =(Button)findViewById(R.id.buttonName);
buttonName.setOnClickListener(startName);
Button buttonType =(Button)findViewById(R.id.buttonType);
buttonType.setOnClickListener(startType);
dEdit =(EditText)findViewById(R.id.textView1);
datab.open();
Cursor c = datab.getAllTitles();
if((c!=null) && c.moveToFirst())
{
do{DisplayTitle(c);
}while (c.moveToNext());
}
datab.open();
Cursor b = datab.getAllTitles();
if ((b!=null) && b.moveToFirst())
DisplayTitle(b);
else
Toast.makeText(this,"No business found",Toast.LENGTH_LONG).show();
data.close();
data.close();
}
//displays the data
public void DisplayTitle(Cursor c) {
Toast.makeText(this,
"Name: " + c.getString(1)+"\n"+
"Address:" + c.getString(2)+"\n"+
"Phone:" + c.getString(3)+"\n"+
"Hours:" + c.getString(4)+"\n"+
"Website"+ c.getShort(5)+
"Type" + c.getShort(6),
Toast.LENGTH_LONG).show();
}
//Informs the user what is being searched
private OnClickListener startName=new OnClickListener(){
public void onClick (View v) {
Cursor cur=data.rawQuery("SELECT business,address,phone,hours,website,type FROM Business where name like %"+dEdit.getText().toString()+"%", null);
String result="";
int iRow=cur.getColumnIndex(KEY_ROWID);
int iName=cur.getColumnIndex(KEY_BUSINESS);
int iAddress=cur.getColumnIndex(KEY_ADDRESS);
int iPhone=cur.getColumnIndex(KEY_PHONE);
int iHours=cur.getColumnIndex(KEY_HOURS);
int iWebsite=cur.getColumnIndex(KEY_WEB);
int iType=cur.getColumnIndex(KEY_TYPE);
Toast.makeText(DBUse.this, "Searching by Name", Toast.LENGTH_LONG).show();
// log.d("result",DBUse.getString(0));
for(cur.moveToFirst(); !cur.isAfterLast(); cur.moveToNext()){
result=result +cur.getString(iRow) + " "
+cur.getString(iName) + " "
+cur.getString(iAddress) + " "
+cur.getString(iPhone) + " "
+cur.getString(iHours) + " "
+cur.getString(iWebsite) + " "
+cur.getString(iType) + " " + "\n";
};
return;
}
};
//Informs the user what is being searched
private OnClickListener startType=new OnClickListener(){
public void onClick (View v){
Cursor cur=data.rawQuery("SELECT business,address,phone,hours,website,type FROM Business where type like %"+dEdit.getText().toString()+"%", null);
String result="";
int iRow=cur.getColumnIndex(KEY_ROWID);
int iName=cur.getColumnIndex(KEY_BUSINESS);
int iAddress=cur.getColumnIndex(KEY_ADDRESS);
int iPhone=cur.getColumnIndex(KEY_PHONE);
int iHours=cur.getColumnIndex(KEY_HOURS);
int iWebsite=cur.getColumnIndex(KEY_WEB);
int iType=cur.getColumnIndex(KEY_TYPE);
Toast.makeText(DBUse.this, "Searching by Name", Toast.LENGTH_LONG).show();
// log.d("result",DBUse.getString(0));
for(cur.moveToFirst(); !cur.isAfterLast(); cur.moveToNext()){
result=result +cur.getString(iRow) + " "
+cur.getString(iName) + " "
+cur.getString(iAddress) + " "
+cur.getString(iPhone) + " "
+cur.getString(iHours) + " "
+cur.getString(iWebsite) + " "
+cur.getString(iType) + " " + "\n";
};
return;
};
};
}
所述清單：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.database"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:debuggable="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.database.DBUse"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
最後的logcat：
04-28 17:27:15.055: E/Trace(721): error opening trace file: No such file or directory (2)
04-28 17:27:16.124: D/dalvikvm(721): GC_FOR_ALLOC freed 47K, 2% free 10842K/11011K, paused 44ms, total 48ms
04-28 17:27:16.134: I/dalvikvm-heap(721): Grow heap (frag case) to 11.204MB for 614416-byte allocation
04-28 17:27:16.274: D/dalvikvm(721): GC_CONCURRENT freed 1K, 2% free 11441K/11655K, paused 76ms+16ms, total 141ms
04-28 17:27:16.324: D/dalvikvm(721): GC_FOR_ALLOC freed 0K, 2% free 11441K/11655K, paused 29ms, total 29ms
04-28 17:27:16.334: I/dalvikvm-heap(721): Grow heap (frag case) to 12.245MB for 1093136-byte allocation
04-28 17:27:16.474: D/dalvikvm(721): GC_CONCURRENT freed 0K, 2% free 12508K/12743K, paused 75ms+6ms, total 132ms
04-28 17:27:16.544: D/AndroidRuntime(721): Shutting down VM
04-28 17:27:16.544: W/dalvikvm(721): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
04-28 17:27:16.556: E/AndroidRuntime(721): FATAL EXCEPTION: main
04-28 17:27:16.556: E/AndroidRuntime(721): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.database/com.example.database.DBUse}: java.lang.NullPointerException
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.os.Handler.dispatchMessage(Handler.java:99)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.os.Looper.loop(Looper.java:137)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-28 17:27:16.556: E/AndroidRuntime(721): at java.lang.reflect.Method.invokeNative(Native Method)
04-28 17:27:16.556: E/AndroidRuntime(721): at java.lang.reflect.Method.invoke(Method.java:511)
04-28 17:27:16.556: E/AndroidRuntime(721): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-28 17:27:16.556: E/AndroidRuntime(721): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-28 17:27:16.556: E/AndroidRuntime(721): at dalvik.system.NativeStart.main(Native Method)
04-28 17:27:16.556: E/AndroidRuntime(721): Caused by: java.lang.NullPointerException
04-28 17:27:16.556: E/AndroidRuntime(721): at com.example.database.DBUse.onCreate(DBUse.java:67)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.Activity.performCreate(Activity.java:5008)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
04-28 17:27:16.556: E/AndroidRuntime(721): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
04-28 17:27:16.556: E/AndroidRuntime(721): ... 11 more
04-28 17:27:18.624: I/Process(721): Sending signal. PID: 721 SIG: 9
對我來說，你釘了它。在閱讀Cursor的文檔時，似乎這些調用不會在空查詢中返回null，就像我認爲的那樣。 – DigCamara 2013-04-28 21:53:39
我應該只是擺脫在創建方法關閉在一起？因爲我最終關閉了數據庫？好吧，這正是我所做的，事情的工作非常感謝！ – aNappyBoi 2013-04-28 22:06:02
@CommonsWare你能幫我解決另一個我得到的nullpointerexception嗎？ – aNappyBoi 2013-04-28 22:11:41