标签:sqlite sqliteopenhelper class android
我在Android应用程序中无法访问SQLite数据库.我创建了一个包含SQLiteOpenHelper实例的应用程序类,但是,每当我尝试在另一个活动中打开数据库时,它就会崩溃.
这是我的应用程序类:
public class GlobalVariables extends Application {
private LocationsData locations;
public void onCreate(Context context) {
locations = new LocationsData(context);
}
public LocationsData getLocations() {
return locations;
}
}
这是我的SQLiteOpenHelper类:
public class LocationsData extends SQLiteOpenHelper{
private static final String DATABASE_NAME = "locations.db";
private static final int DATABASE_VERSION = 1;
public static final String TABLE_LOCATIONS = "locations";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_NICKNAME = "nickname";
private static final String DATABASE_CREATE = "create table "
+ TABLE_LOCATIONS + "( " + COLUMN_ID
+ " integer primary key autoincrement, " + COLUMN_NICKNAME
+ " text not null);";
public LocationsData(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOCATIONS);
onCreate(db);
}
}
当我尝试在另一个活动中访问数据库时,出现错误:
@Override
public void onResume()
{
locationsData=((GlobalVariables)getApplication()).getLocations();
SQLiteDatabase db = locationsData.getReadableDatabase();
super.onResume();
}
有什么帮助吗?谢谢!
Log Cat:
05-10 02:00:50.146: D/AndroidRuntime(532): Shutting down VM
05-10 02:00:50.146: W/dalvikvm(532): threadid=1: thread exiting with uncaught exception (group=0x40015560)
05-10 02:00:50.179: E/AndroidRuntime(532): FATAL EXCEPTION: main
05-10 02:00:50.179: E/AndroidRuntime(532): java.lang.RuntimeException: Unable to resume activity {com.John.seniorDesign/com.John.seniorDesign.LocationsTabActivity}: java.lang.NullPointerException
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2120)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:138)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.widget.TabHost.setCurrentTab(TabHost.java:326)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:132)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:456)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.view.View.performClick(View.java:2485)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.view.View$PerformClick.run(View.java:9080)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.os.Handler.handleCallback(Handler.java:587)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.os.Handler.dispatchMessage(Handler.java:92)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.os.Looper.loop(Looper.java:130)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.ActivityThread.main(ActivityThread.java:3683)
05-10 02:00:50.179: E/AndroidRuntime(532): at java.lang.reflect.Method.invokeNative(Native Method)
05-10 02:00:50.179: E/AndroidRuntime(532): at java.lang.reflect.Method.invoke(Method.java:507)
05-10 02:00:50.179: E/AndroidRuntime(532): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-10 02:00:50.179: E/AndroidRuntime(532): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-10 02:00:50.179: E/AndroidRuntime(532): at dalvik.system.NativeStart.main(Native Method)
05-10 02:00:50.179: E/AndroidRuntime(532): Caused by: java.lang.NullPointerException
05-10 02:00:50.179: E/AndroidRuntime(532): at com.John.seniorDesign.LocationsTabActivity.onResume(LocationsTabActivity.java:75)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1150)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.Activity.performResume(Activity.java:3832)
05-10 02:00:50.179: E/AndroidRuntime(532): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2110)
05-10 02:00:50.179: E/AndroidRuntime(532): ... 17 more
解决方法:
在GlobalVariables中,将上下文更改为新的LocationsData中的getApplicationContext()并从onCreate中删除上下文-此签名不存在.
编辑:
public class GlobalVariables extends Application {
private LocationsData locations;
@Override
public void onCreate() {
locations = new LocationsData(getApplicationContext());
}
public LocationsData getLocations() {
return locations;
}
}
标签:sqlite,sqliteopenhelper,class,android 来源: https://codeday.me/bug/20191101/1982950.html
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