eclipse中android sdk中的内容提供者

Question

我想为我的 Android 应用程序创建一个数据库。我在我的项目中编写了数据库的代码；每当我运行时，它都会在模拟器上显示“强制关闭”。我尝试过不同的方法，但没有任何效果。我哪里做错了？

// EventContentProvider.java                  
package com.event.test;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;

public class EventContentProvider extends ContentProvider {

private static final String DATABASE_NAME = "event.db";

private static final UriMatcher sUriMatcher;
private static final int EVENTS = 1;
private static final int EVENT_ID = 2;

private static class DatabaseHelper extends SQLiteOpenHelper {

public DatabaseHelper(Context context) {

        super(context, DATABASE_NAME, null, 1);
    }

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE event1 (_ID INTEGER PRIMARY KEY,                   first_name       TEXT, last_name TEXT);");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
 }

 private DatabaseHelper mOpenHelper;

    @Override
 public boolean onCreate() {
 mOpenHelper = new DatabaseHelper(getContext());
 return true;
}

@Override
public int delete(Uri uri, String where, String[] whereArgs) {
    SQLiteDatabase db = null;
    int count = 0;
    try {
        db = mOpenHelper.getWritableDatabase();
        switch(sUriMatcher.match(uri)){
        case EVENTS:
        count = db.delete(Event.EVENT_TABLE_NAME, where, whereArgs);
            break;
        default:
            throw new IllegalArgumentException("No content matched");
        }
        getContext().getContentResolver().notifyChange(uri, null);
    } catch(Exception e) {
    } finally {
        if(db != null)
            db.close();
    }
    return count;
}

@Override
public String getType(Uri uri) {
    switch(sUriMatcher.match(uri)){
    case EVENTS:
        return Event.CONTENT_TYPE;
    default:
        throw new IllegalArgumentException("No content matched");
    }
}

@Override
public Uri insert(Uri uri, ContentValues initialValues) {

    SQLiteDatabase db = mOpenHelper.getWritableDatabase();
    ContentValues values;
    if (initialValues != null) {
        values = new ContentValues(initialValues);
    } else {
        values = new ContentValues();
    }
    long rowId = -1;
    Uri contentUri = null;
    switch(sUriMatcher.match(uri)){
    case EVENTS:
    rowId = db.insertOrThrow(Event.EVENT_TABLE_NAME, Event._ID, values);
        contentUri = ContentUris.withAppendedId(Event.CONTENT_URI, rowId);
        break;
    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }
    db.close();

    if(rowId > 0){
        return contentUri;
    }

    return null;
}

@Override
 public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
    SQLiteDatabase db = mOpenHelper.getWritableDatabase();

    long rowId = -1;
    try {
        switch (sUriMatcher.match(uri)) {
        case EVENTS:
        rowId = db.update(Event.EVENT_TABLE_NAME, values, selection,
                    selectionArgs);
            break;
        default:
            throw new IllegalArgumentException("Unknown URI " + uri);

        }
        rowId = db.update(Event.EVENT_TABLE_NAME, values, selection,
                selectionArgs);
    } catch (Exception e) {
    } finally {
        if(db != null)
            db.close();
    }

    return (int) rowId;
}



@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

    switch(sUriMatcher.match(uri)){
    case EVENTS:
        qb.setTables(Event.EVENT_TABLE_NAME);
        qb.setProjectionMap(Event.sEventProjectionMap);
        break;
    default:
    throw new IllegalArgumentException("No content matched in query ");
    }

    SQLiteDatabase db = null;
    Cursor c = null;
    try {
        db = mOpenHelper.getReadableDatabase();
c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder);
        c.setNotificationUri(getContext().getContentResolver(), uri);
    } catch (Exception e) {
    }
    return c;
}


static {
    sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    sUriMatcher.addURI(Event.AUTHORITY, "events", EVENTS);
    sUriMatcher.addURI(Event.AUTHORITY, "events/#", EVENT_ID);
}


}
//Event.java
package com.event.test;

import java.util.HashMap;
import android.net.Uri;
import android.provider.BaseColumns;

public class Event implements BaseColumns{

public static final String AUTHORITY = "com.event.data.contentprovider";
public static final Uri CONTENT_URI =    Uri.parse("content://com.event.data.contentprovider/events");
public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.event.event";
public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.event/vnd.event.event";


public static final String EVENT_TABLE_NAME = "event1";
public static final String FIRSTNAME = "first_name";
public static final String LASTNAME = "last_name";
public static String _ID;


public static HashMap<String,String> sEventProjectionMap;

static {
    Event.sEventProjectionMap = new HashMap<String,String>();
    Event.sEventProjectionMap.put(Event._ID, Event._ID);
    Event.sEventProjectionMap.put(Event.FIRSTNAME, Event.FIRSTNAME);
    Event.sEventProjectionMap.put(Event.LASTNAME, Event.LASTNAME);

}
}
//manifestfile.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.event.test"
  android:versionCode="1"
  android:versionName="1.0">
<uses-sdk android:minSdkVersion="10" />

<application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".EventManagementActivity"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
<provider android:name="com.event.test.EventContentProvider"
              android:authorities="com.event.data.contentprovider" />
</application>
</manifest>
//EventManagementActivity.java
package com.event.test;

 import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class EventManagementActivity extends Activity implements OnClickListener{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button btn = (Button) findViewById(R.id.btn01);
    btn.setText("Press Me");
    btn.setOnClickListener(this);


}

@Override
public void onClick(View arg0) 
{
    switch(arg0.getId()){
    case R.id.btn01:
    ContentValues cv = new ContentValues();
    cv.put(Event.FIRSTNAME, "DATTA");
    cv.put(Event.LASTNAME, "Prabhu");
    getContentResolver().insert(Event.CONTENT_URI, cv);


    String[] str = {Event.FIRSTNAME, Event.LASTNAME};
    String where = Event.FIRSTNAME + " = ? AND " + 
                    Event.LASTNAME + " = ?";

    String [] whereArgs = {"Datta", "Prabhu"};
    Cursor c = getContentResolver().query(Event.CONTENT_URI, 
        str, 
        where, 
            whereArgs, 
            null);
    if (c.moveToFirst() ) {
    int id = c.getInt(0);
    String firstName = c.getString(0);
    String lastName = c.getString(1);
 EditText edit = (EditText) findViewById(R.id.edit01);
 edit.setText( id + firstName + " " + lastName);
 TextView tv = (TextView) findViewById(R.id.text01);
 tv.setText(id + firstName + " " + lastName);
    }

    c.close();
    break;

}
}
 }
//main.xml
<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
 >
 <TextView  
android:layout_width="fill_parent" 
android:layout_height="wrap_content" 
android:text=""
android:id="@+id/text01"
/>
<EditText
android:id="@+id/edit01"
android:layout_width="fill_parent"
android:layout_height="wrap_content" 
/>
<Button 
android:id="@+id/btn01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
 </LinearLayout>

//R.java    
 package com.event.test;

 public final class R {
public static final class attr {
}
public static final class drawable {
    public static final int icon=0x7f020000;
}
public static final class id {
    public static final int btn01=0x7f050002;
    public static final int edit01=0x7f050001;
    public static final int text01=0x7f050000;
}
public static final class layout {
    public static final int main=0x7f030000;
}
public static final class string {
    public static final int app_name=0x7f040001;
    public static final int hello=0x7f040000;
  }
 }
//logcat
 10-04 01:12:06.904: DEBUG/MediaScanner(285):    total time: 981ms
 10-04 01:12:06.984: DEBUG/MediaScannerService(285): done scanning volume internal
 10-04 01:12:07.344: DEBUG/dalvikvm(216): GC_CONCURRENT freed 243K, 51% free          2798K/5703K, external 410K/517K, paused 4ms+3ms
 10-04 01:12:07.854: DEBUG/dalvikvm(178): GC_EXPLICIT freed 331K, 50% free 2952K/5895K, external 1313K/1400K, paused 64ms
 10-04 01:12:12.318: WARN/ActivityManager(73): Activity destroy timeout for HistoryRecord{4072bb18 com.event.test/.EventManagementActivity}
 10-04 01:12:15.079: INFO/InputReader(73): Device reconfigured: id=0x0, name=qwerty2, display size is now 240x432
 10-04 01:12:15.079: INFO/InputManager-Callbacks(73): No virtual keys found for device qwerty2.
 10-04 01:12:15.653: INFO/ARMAssembler(73): generated scanline__00000177:03515104_00001001_00000000 [ 91 ipp] (114 ins) at [0x44325520:0x443256e8] in 1138243 ns
 10-04 01:12:16.543: INFO/dalvikvm(73): Jit: resizing JitTable from 512 to 1024
 10-04 01:12:18.393: INFO/Process(239): Sending signal. PID: 239 SIG: 9
 10-04 01:12:18.403: INFO/ActivityManager(73): Process com.event.test (pid 239) has died.
 10-04 01:12:21.153: DEBUG/dalvikvm(178): GC_EXTERNAL_ALLOC freed 61K, 51% free 2947K/5895K, external 1202K/1400K, paused 48ms
 10-04 01:12:24.723: INFO/ActivityManager(73): Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.event.test/.EventManagementActivity } from pid 178
 10-04 01:12:24.773: INFO/ActivityManager(73): Start proc com.event.test for activity com.event.test/.EventManagementActivity: pid=335 uid=10034 gids={}
 10-04 01:12:25.253: INFO/ARMAssembler(73): generated scanline__00000177:03515104_00001002_00000000 [ 87 ipp] (110 ins) at [0x443256f0:0x443258a8] in 551089 ns
 10-04 01:12:25.303: INFO/ActivityThread(335): Pub com.event.data.contentprovider: com.event.test.EventContentProvider
 10-04 01:12:25.583: DEBUG/AndroidRuntime(335): Shutting down VM
 10-04 01:12:25.583: WARN/dalvikvm(335): threadid=1: thread exiting with uncaught exception (group=0x40015560)
  10-04 01:12:25.594: ERROR/AndroidRuntime(335): FATAL EXCEPTION: main
  10-04 01:12:25.594: ERROR/AndroidRuntime(335): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.event.test/com.event.test.EventManagementActivity}: java.lang.NullPointerException
  10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.os.Handler.dispatchMessage(Handler.java:99)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.os.Looper.loop(Looper.java:123)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.main(ActivityThread.java:3683)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at java.lang.reflect.Method.invokeNative(Native Method)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at java.lang.reflect.Method.invoke(Method.java:507)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at dalvik.system.NativeStart.main(Native Method)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335): Caused by: java.lang.NullPointerException
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at com.event.test.EventManagementActivity.onCreate(EventManagementActivity.java:21)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
 10-04 01:12:25.594: ERROR/AndroidRuntime(335):     ... 11 more
 10-04 01:12:25.603: WARN/ActivityManager(73):   Force finishing activity com.event.test/.EventManagementActivity
 10-04 01:12:26.123: WARN/ActivityManager(73): Activity pause timeout for HistoryRecord{4070aaa0 com.event.test/.EventManagementActivity}
 10-04 01:12:27.503: INFO/Process(335): Sending signal. PID: 335 SIG: 9
 10-04 01:12:27.543: WARN/InputManagerService(73): Window already focused, ignoring focus gain of: com.android.internal.view.IInputMethodClient$Stub$Proxy@4073ba40
 10-04 01:12:27.874: INFO/ActivityManager(73): Process com.event.test (pid 335) has died.
 10-04 01:12:36.575: WARN/ActivityManager(73): Activity destroy timeout for HistoryRecord{4070aaa0 com.event.test/.EventManagementActivity}

Answer 1

堆栈跟踪会向您指出导致问题的确切代码行：

 at com.event.test.EventManagementActivity.onCreate(EventManagementActivity.java:21)

虽然堆栈跟踪可能看起来令人困惑，但它非常有用。关键是查看所有 Android 类，并跟踪到您的类：

com.event.test.EventManagementActivity.onCreate(EventManagementActivity.java:21) ... 21 表示第 21 行。

空指针异常通常意味着某些东西没有被实例化。调试并单步检查到这一行的变量。您正在引用空的东西。