Android Studio：PutExtra＆amp; GetStringExtra与在线数据库（没有价值）

Question

我是移动应用程序开发的初学者，目前我正在进行登录（在线数据库）和Register.I想通过使用putExtra和getStringExtra将一些参数传递给下一个活动。以下是我的两项活动代码：

登录：

的

的

public class Login extends AppCompatActivity implements View.OnClickListener {
Button bLogin;
TextView registerLink;
EditText etUsername, etPassword;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);

    bLogin = (Button) findViewById(R.id.bLogin);
    etUsername = (EditText) findViewById(R.id.etUsername);
    etPassword = (EditText) findViewById(R.id.etPassword);
    registerLink = (TextView) findViewById(R.id.tvRegisterLink);


    bLogin.setOnClickListener(this);
    registerLink.setOnClickListener(this);



}

@Override
public void onClick(View view) {
    switch (view.getId()) {
        case R.id.bLogin:
            String Username = etUsername.getText().toString();
            String Password = etPassword.getText().toString();
            Toast.makeText(this, "Loginin...", Toast.LENGTH_SHORT).show();
            new Authenticate(this).execute(Username, Password);





            break;
        case R.id.tvRegisterLink:
            Intent registerIntent = new Intent(Login.this, Register.class);
            startActivity(registerIntent);
            break;
    }
}






public void ParentLogin()
{

    String Username = etUsername.getText().toString();
    String Password = etPassword.getText().toString();
    Intent Main = new Intent(Login.this, MainActivity.class);
    Main.putExtra("class","Parent");
    Main.putExtra("username",Username);
    Main.putExtra("password",Password);
    startActivity(Main);

}
public void NannyLogin()
{

    String Username = etUsername.getText().toString();
    String Password = etPassword.getText().toString();
    Intent Main = new Intent(Login.this, MainActivity.class);
    Main.putExtra("class", "Nanny");
    Main.putExtra("username",Username);
    Main.putExtra("password",Password);
    startActivity(Main);

}

public class Authenticate extends AsyncTask<String, Void, String> {

    private Context context;

    public Authenticate(Context context) {
        this.context = context;
    }

    @Override
    protected void onPreExecute() {

    }
    @Override
    protected String doInBackground(String... arg0) {
        String Username = arg0[0];
        String Password = arg0[1];

        String link;
        String data;
        BufferedReader bufferedReader;
        String result;

        try {

            data = "?username=" + URLEncoder.encode(Username, "UTF-8");
            data += "&password=" + URLEncoder.encode(Password, "UTF-8");


            link = "http://juliusgoh.comxa.com/Authenticate.php" + data;
            URL url = new URL(link);
            HttpURLConnection con = (HttpURLConnection) url.openConnection();

            bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
            result = bufferedReader.readLine();
            return result;
        } catch (Exception e) {
            return ("Exception: " + e.getMessage());
        }

    }

    @Override
    protected void onPostExecute(String result) {
        if (result != null) {
            try {
                JSONObject jsonObj = new JSONObject(result);
                String query_result = jsonObj.getString("query_result");
                switch (query_result) {
                    case "PSUCCESS":
                        Toast.makeText(context, "Login Successfully....Parent", Toast.LENGTH_SHORT).show();
                        ParentLogin();
                        break;
                    case "NSUCCESS":
                        Toast.makeText(context, "Login Successfully....Nanny", Toast.LENGTH_SHORT).show();
                        NannyLogin();
                        break;
                    case "FAILURE":
                        Toast.makeText(context, "Wrong Data. Login failed.", Toast.LENGTH_SHORT).show();
                        break;
                    default:
                        Toast.makeText(context, "Couldn't connect to remote database.", Toast.LENGTH_SHORT).show();
                        break;
                }
            } catch (JSONException e) {
                e.printStackTrace();
                Toast.makeText(context, "Error parsing JSON data.", Toast.LENGTH_SHORT).show();
            }
        } else {
            Toast.makeText(context, "Couldn't get any JSON data.", Toast.LENGTH_SHORT).show();
        }
    }
}

的

第二项活动：

的

的

公共类MainActivity扩展了AppCompatActivity {

public String job;
public String username;
public String password;
TextView qwe;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    qwe = (TextView)findViewById(R.id.asd);
    Intent intent = new Intent();
    String strValue = intent.getStringExtra("class");
    String strValue1 = intent.getStringExtra("username");
    String strValue2 = intent.getStringExtra("password");
    qwe.setText(strValue);
      }

的

代码工作正常，但在第二个活动中它没有显示任何内容。我猜它通过＆＃34;＆＃34; null argument.But我不知道如何解决它。请提供一些建议。 TQ <3

Answer 1

我找到了问题的解决方案，我的第二个活动应该输入Intent intent = getIntent（）;而不是Intent intent = new Intent;