如何添加一個OnClicklistener到這種類型的代碼

Question

我們的應用程序應該連接到一個SQL數據庫。它在我們的網絡中。該應用程序應該編輯數據庫中的數據。我們已經建立了連接，並且想要將一個onclicklistener設置爲Button，這會導致連接代碼連接。

這是我們已經得到了代碼：

public class Werte_aendern extends AppCompatActivity { 

TextView tvIP; 

String Textauslesen = tvIP.getText().toString(); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    tvIP = (TextView) findViewById(R.id.tvIP); 
    setContentView(R.layout.activity_werte_aendern); 
} 




    Connection con = null; 
    //private static String dbHost = "192.168.40.148"; // Hostname 
    String dbPort = "3306";  // Port -- Standard: 3306 
    String dbName = "wasserwerte"; // Datenbankname 
    String dbUser = "App";  // Datenbankuser 
    String dbPass = "fruitcake";  // Datenbankpasswort 

    private Werte_aendern(){ 
     try { 
      Class.forName("com.mysql.jdbc.Driver"); // Datenbanktreiber für JDBC Schnittstellen laden. 

      // Verbindung zur JDBC-Datenbank herstellen. 
      con = DriverManager.getConnection("jdbc:mysql://"+Textauslesen+":"+ dbPort+"/"+dbName+"?"+"user="+dbUser+"&"+"password="+dbPass); 
      // Statement createStatement(); 
      // SQLiteDatabase wasserwerte = 

     } catch (ClassNotFoundException e) { 
      Toast.makeText(getApplicationContext(), "Treiber nicht gefunden", Toast.LENGTH_SHORT).show(); 
     } catch (SQLException e) { 
      Toast.makeText(getApplicationContext(), "Verbindung nicht möglich", Toast.LENGTH_SHORT).show(); 
      Toast.makeText(getApplicationContext(), "SQLException: " + e.getMessage(), Toast.LENGTH_SHORT).show(); 
      Toast.makeText(getApplicationContext(), "SQLState: " + e.getSQLState(), Toast.LENGTH_SHORT).show(); 
      Toast.makeText(getApplicationContext(), "VendorError: " + e.getErrorCode(), Toast.LENGTH_SHORT).show(); 
     } 
    } 

} 

我們是菜鳥，但我們必須爲schoolproject做到這一點。
你能幫助我們嗎？

Answer 1

我已更新您的代碼。活動應始終命名爲[無論]活動。如果因爲我不會說德語（我認爲它是德語），所以「WerteAndern」是一個正確的名字。

public class WerteAendernActivity extends AppCompatActivity { 

    TextView tvIP; 

    // You should get the text from the View AFTER inflating the layout and find it with 
    // findViewById. Otherwise it's gonna crash. 
    String textauslesen; 
    private Button connectBtn; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // First you inflate the layout 
     setContentView(R.layout.activity_werte_aendern); 
     // Then you get the views 
     tvIP = (TextView) findViewById(R.id.tvIP); 
     // Probably should be somewhere else as there is no interesting text to retrieve from the 
     // view at the moment 
     textauslesen = tvIP.getText().toString(); 

     connectBtn = (Button) findViewById(R.id.connection_button); // ! You need to add a Button in your layout 
     connectBtn.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       // Add some test, ... if you're already connected 
       connectToDataBase(); 
      } 
     }); 
    } 

    Connection con = null; 
    //private static String dbHost = "192.168.40.148"; // Hostname 
    String dbPort = "3306";  // Port -- Standard: 3306 
    String dbName = "wasserwerte"; // Datenbankname 
    String dbUser = "App";  // Datenbankuser 
    String dbPass = "fruitcake";  // Datenbankpasswort 


    // Method to connect to the database. 
    // !!! You're not supposed to override the constructor of an Activity! 
    private void connectToDataBase() { 
     try { 
      Class.forName("com.mysql.jdbc.Driver"); // Datenbanktreiber für JDBC Schnittstellen laden. 

      // Verbindung zur JDBC-Datenbank herstellen. 
      con = DriverManager.getConnection("jdbc:mysql://" + textauslesen + ":" + dbPort + "/" + dbName + "?" + "user=" + dbUser + "&" + "password=" + dbPass); 
      // Statement createStatement(); 
      // SQLiteDatabase wasserwerte = 

     } catch (ClassNotFoundException e) { 
      Toast.makeText(getApplicationContext(), "Treiber nicht gefunden", Toast.LENGTH_SHORT).show(); 
      e.printStackTrace(); 
     } catch (SQLException e) { 
      Toast.makeText(getApplicationContext(), "Error! See Exception logs", Toast.LENGTH_SHORT).show(); 
      // The logs will be displayed in the Logcat window in Android Studio 
      e.printStackTrace(); 
     } 
    } 
}