我制作了一个扫描qr代码的应用。我希望将从qr代码扫描的数据（如2300,2301,2302之类的数字）与sqlite数据库中名为ID的列进行比较。 sqlite数据库中列ID的一些值是2301,2302,2303。我希望扫描的数据与ID中的值进行比较，如果匹配，则执行操作。如果不是，将显示错误消息。如果qr代码具有值2301，则将执行该动作。如果它是8900（数据库中没有的数字），则会显示一条消息：找不到学生。我还想澄清一下，扫描数据没有输入sqlite数据库，而是发送到谷歌脚本链接。 sqlite数据库包含学生列表。我希望如果扫描的数据与sqlite数据库中的nay ID不相似，那么sannedData将不会发送到谷歌应用程序脚本目标。 这是我的数据库代码，用于活动DatabaseHelper
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "Student.db";
public static final String TABLE_NAME = "student_table";
public static final String COL_1 = "ID";
public static final String COL_2 = "NAME";
public static final String COL_3 = "SURNAME";
public static final String COL_4 = "MARKS";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + TABLE_NAME +" (ID INT PRIMARY KEY UNIQUE,NAME TEXT,SURNAME TEXT,MARKS TEXT)");
}
下面是我想要修改的代码，以检查它是否在数据库中。这是另一项名为MainActivity的活动。
public class ArrivalTime extends AppCompatActivity {
String scannedData;
Button scanBtn;
//-----------------------------------------------------------
//DatabaseHelper myDb;
//------------------------------------------------------------
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_arrival_time);
final Activity activity = this;
scanBtn = (Button) findViewById(R.id.scan_btn);
//-------------------------------------------------------
// myDb = new DatabaseHelper(this);
//---------------------------------------------------------
scanBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
IntentIntegrator integrator = new IntentIntegrator(activity);
integrator.setDesiredBarcodeFormats(IntentIntegrator.ALL_CODE_TYPES);
integrator.setPrompt("Place barcode in window to Scan it");
integrator.setBeepEnabled(true);
integrator.setCameraId(0);
integrator.setBarcodeImageEnabled(false);
integrator.initiateScan();
}
});
}
//-----------------------------------------------------------------------------------------
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
IntentResult result= IntentIntegrator.parseActivityResult(requestCode,resultCode,data);
if(result!=null){
scannedData = result.getContents();
if(scannedData != null){
// here we need to handle scanned data
// Cursor c = myDb.getId(String);
// if(c.getCount() == 0) {
// show message
// Toast.makeText(ArrivalTime.this,"Student doesn't exist in database",Toast.LENGTH_LONG).show();
// return;
//}
new SendRequest().execute();
}
else{
}
}
super.onActivityResult(requestCode, resultCode, data);
}
//-----------------------------------------------------------------------------------------
public class SendRequest extends AsyncTask<String, Void, String>{
protected void onPreExecute(){}
protected String doInBackground(String... arg0){
try{
URL url = new URL("https://script.google.com/macros/s/ttttttttttttttttttttttttttttttttttttttttttttt/exec");
JSONObject postDataParams = new JSONObject();
postDataParams.put("sdata",scannedData);
Log.e("params", postDataParams.toString());
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(15000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.setDoOutput(true);
OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(os, "UTF-8"));
writer.write(getPostDataString(postDataParams));
writer.flush();
writer.close();
os.close();
int responseCode=conn.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK) {
BufferedReader in=new BufferedReader(new InputStreamReader(conn.getInputStream()));
StringBuffer sb = new StringBuffer("");
String line="";
while((line = in.readLine()) != null) {
sb.append(line);
break;
}
in.close();
return sb.toString();
}
else {
return new String("false : "+responseCode);
}
}
catch(Exception e){
return new String("Exception: " + e.getMessage());
}
}
@Override
protected void onPostExecute(String result) {
Toast.makeText(getApplicationContext(), result,
Toast.LENGTH_LONG).show();
}
}
public String getPostDataString(JSONObject params) throws Exception {
StringBuilder result = new StringBuilder();
boolean first = true;
Iterator<String> itr = params.keys();
while(itr.hasNext()){
String key= itr.next();
Object value = params.get(key);
if (first)
first = false;
else
result.append("&");
result.append(URLEncoder.encode(key, "UTF-8"));
result.append("=");
result.append(URLEncoder.encode(value.toString(), "UTF-8"));
}
return result.toString();
}
//-----------------------------------------------------------------------------------------
我希望函数检查扫描的数据是否为空并且数据库中是否存在。我尝试过if（scanningData！= null＆amp;＆amp;＆scan; = id）但我不确定如何从另一个活动调用数据库数据并执行比较
我在下面给出了一个例子，但它假设我正在检查是否存在与扫描的内容相似的值，以便可以将其输入sqlite数据库，这不是我想要的。
任何建议。
答案 0 :(得分：0)
您可以查看如下..
@Data
@Entity
@Table(name = "user_card")
public class UserCard implements Serializable {
@Id
@ManyToOne
@JoinColumn(name = "user_id", nullable = false)
private User user;
@Id
@ManyToOne
@JoinColumn(name = "card_id", nullable = false)
private Card card;
@Column(name = "cardCount", nullable = false)
private int cardCount;
}
答案 1 :(得分：0)
答案非常简单，您必须使用ID列的给定值进行选择查询，并像这样检查Cursor.getCount（）方法。
Cursor.getCount(); // returns number of rows from this query。
如果它返回0，那么那里有一些行意味着ID确实存在
public boolean Contains(String ID) {
Cursor cursor = null;
cursor = db.rowQuery("SELECT * FROM student_table WHERE ID === ? ", new String[]{ID});
if (cursor.getCount() == 0) {
return false;
}
return true;
}