安卓:在返回数量SQLite数据库崩溃 [英] Android: SQLite database crashes on returning a quantity
问题描述
数据库保存的名称和药物的数量...需要什么要返回是对应于被扫描的药物的数量。
code数据库:
公共类ToolDB { 公共静态最后弦乐KEY_ROWID =ID;
公共静态最后弦乐KEY_NAME =名;
公共静态最后弦乐KEY_QUANTITY =量;
私有静态最后弦乐TAG =DBAdapter; 私有静态最后弦乐DATABASE_NAME =Medicine_Database;
私有静态最后弦乐DATABASE_TABLE =meds_db;
私有静态最终诠释DATABASE_VERSION = 2; 私有静态最后弦乐DATABASE_CREATE =
创建表,如果不存在meds_db(ID整数主键自动增量
+名VARCHAR NOT NULL,数量VARCHAR);;
公共字符串QuantReturn(){ UserInput X =新UserInput();
字符串Y = x.QR codeReturn(); 字符串量=无效;
字符串selectQuery =SELECT量从meds_db其中name =+ Y;
光标C = db.rawQuery(selectQuery,NULL); 如果(零= C和;!&放大器; c.moveToFirst()){
量= c.getString(c.getColumnIndex(KEY_QUANTITY));
}
返回数量;
}
QR codeReturn()方法的工作,当你对自己的运行它,它返回从QR code读取正确的字符串。
类执行时崩溃:
公共类测试扩展活动{@覆盖
保护无效的onCreate(捆绑savedInstanceState){
super.onCreate(savedInstanceState);
的setContentView(R.layout.activity_testing); ToolDB DB =新ToolDB(本); db.open();
串C1 = db.QuantReturn();
db.close();
TextView的T3 =(的TextView)findViewById(R.id.slot4);
t3.setText(C1);}
LogCat中发生错误:
03-18 21:24:58.310:E / AndroidRuntime(14192):致命异常:主要
03-18 21:24:58.310:E / AndroidRuntime(14192):了java.lang.RuntimeException:无法启动活动ComponentInfo {com.example.SurgicalMate / com.example.SurgicalMate.Testing}:显示java.lang.NullPointerException
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread.access $ 600(ActivityThread.java:151)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1331)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.os.Handler.dispatchMessage(Handler.java:99)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.os.Looper.loop(Looper.java:155)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread.main(ActivityThread.java:5454)
03-18 21:24:58.310:E / AndroidRuntime(14192):在java.lang.reflect.Method.invokeNative(本机方法)
03-18 21:24:58.310:E / AndroidRuntime(14192):在java.lang.reflect.Method.invoke(Method.java:511)
03-18 21:24:58.310:E / AndroidRuntime(14192):在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1029)
03-18 21:24:58.310:E / AndroidRuntime(14192):在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
03-18 21:24:58.310:E / AndroidRuntime(14192):在dalvik.system.NativeStart.main(本机方法)
03-18 21:24:58.310:E / AndroidRuntime(14192):致:显示java.lang.NullPointerException
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.content.ContextWrapper.getShared preferences(ContextWrapper.java:153)
03-18 21:24:58.310:E / AndroidRuntime(14192):在com.example.SurgicalMate.UserInput.QR codeReturn(UserInput.java:76)
03-18 21:24:58.310:E / AndroidRuntime(14192):在com.example.SurgicalMate.ToolDB.QuantReturn(ToolDB.java:78)
03-18 21:24:58.310:E / AndroidRuntime(14192):在com.example.SurgicalMate.Testing.onCreate(Testing.java:24)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.Activity.performCreate(Activity.java:5066)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101)
03-18 21:24:58.310:E / AndroidRuntime(14192):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
03-18 21:24:58.310:E / AndroidRuntime(14192):... 11个
QR codeReturn()方法返回一个字符串。我在其他地方测试,它一直工作正常。
公共字符串QR codeReturn(){ 共享preferences codeHACK = getShared preferences(SCAN_RESULT,0);
字符串QR code = codeHack.getString(项,未登记); 返回QR code;
}
QR codeReturn()
,因为它是现在才能正常工作,如果它有一个适当的上下文
(它需要它 getShared preferences()
梅托德工作)。它不会从类`ToolDB工作。
您应该:
- 要么通过一个
上下文
参数,将其 - 或交替运行您的活动这种方法,并通过所获得的值
ToolDB
类。
使用
ToolDB
上课前例如:
公共字符串QR codeReturn(上下文的背景下){ 共享preferences codeHACK = context.getShared preferences(SCAN_RESULT,0);
字符串QR code = codeHack.getString(项,未登记); 返回QR code;
}
然后,您可以使用它从活动:
字符串code = QR codeReturn(本);
和 QuantReturn()
:
公共字符串QuantReturn(上下文的背景下){ ...
字符串Y = x.QR codeReturn(背景);
...
}
Database holds name and quantity of medication... what is required to be returned is the quantity corresponding to the medication which is scanned. code for database:
public class ToolDB {
public static final String KEY_ROWID = "id";
public static final String KEY_NAME = "name";
public static final String KEY_QUANTITY = "quantity";
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "Medicine_Database";
private static final String DATABASE_TABLE = "meds_db";
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_CREATE =
"create table if not exists meds_db (id integer primary key autoincrement, "
+ "name VARCHAR not null, quantity VARCHAR);";
public String QuantReturn(){
UserInput x = new UserInput();
String y = x.QRcodeReturn();
String quantity=null;
String selectQuery = "SELECT quantity FROM meds_db WHERE name = " + y;
Cursor c = db.rawQuery(selectQuery, null);
if(null != c && c.moveToFirst()){
quantity = c.getString(c.getColumnIndex(KEY_QUANTITY));
}
return quantity;
}
QRcodeReturn() method works when you run it on its own and it returns the proper string read from a QR code.
class that crashes when executed:
public class Testing extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_testing);
ToolDB db = new ToolDB(this);
db.open();
String c1 = db.QuantReturn();
db.close();
TextView t3 = (TextView) findViewById(R.id.slot4);
t3.setText(c1);
}
Logcat where the error occurs:
03-18 21:24:58.310: E/AndroidRuntime(14192): FATAL EXCEPTION: main
03-18 21:24:58.310: E/AndroidRuntime(14192): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.SurgicalMate/com.example.SurgicalMate.Testing}: java.lang.NullPointerException
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread.access$600(ActivityThread.java:151)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1331)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.os.Handler.dispatchMessage(Handler.java:99)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.os.Looper.loop(Looper.java:155)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread.main(ActivityThread.java:5454)
03-18 21:24:58.310: E/AndroidRuntime(14192): at java.lang.reflect.Method.invokeNative(Native Method)
03-18 21:24:58.310: E/AndroidRuntime(14192): at java.lang.reflect.Method.invoke(Method.java:511)
03-18 21:24:58.310: E/AndroidRuntime(14192): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
03-18 21:24:58.310: E/AndroidRuntime(14192): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
03-18 21:24:58.310: E/AndroidRuntime(14192): at dalvik.system.NativeStart.main(Native Method)
03-18 21:24:58.310: E/AndroidRuntime(14192): Caused by: java.lang.NullPointerException
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:153)
03-18 21:24:58.310: E/AndroidRuntime(14192): at com.example.SurgicalMate.UserInput.QRcodeReturn(UserInput.java:76)
03-18 21:24:58.310: E/AndroidRuntime(14192): at com.example.SurgicalMate.ToolDB.QuantReturn(ToolDB.java:78)
03-18 21:24:58.310: E/AndroidRuntime(14192): at com.example.SurgicalMate.Testing.onCreate(Testing.java:24)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.Activity.performCreate(Activity.java:5066)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101)
03-18 21:24:58.310: E/AndroidRuntime(14192): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
03-18 21:24:58.310: E/AndroidRuntime(14192): ... 11 more
QRcodeReturn() method returns a string.. I have tested it elsewhere and it has worked correctly.
public String QRcodeReturn(){
SharedPreferences codeHack = getSharedPreferences(SCAN_RESULT,0);
String QRcode = codeHack.getString("entry", "unregistered");
return QRcode;
}
QRcodeReturn()
as it is now will only work correctly if it has a proper Context
(it needs it for getSharedPreferences()
metod to work). It won't work from class `ToolDB.
You should :
- either pass a
Context
parameter to it - or alternatively run this method from your activity before using
ToolDB
class and pass the obtained value toToolDB
class.
For example:
public String QRcodeReturn(Context context){
SharedPreferences codeHack = context.getSharedPreferences(SCAN_RESULT,0);
String QRcode = codeHack.getString("entry", "unregistered");
return QRcode;
}
You can then use it from the activity:
String code = QRcodeReturn(this);
and from QuantReturn()
:
public String QuantReturn(Context context){
...
String y = x.QRcodeReturn(context);
...
}
这篇关于安卓:在返回数量SQLite数据库崩溃的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!