Android Studio MainActivity.java 中的多个 onCreate 方法

Question

For a school project I am creating a simple app. However, I run into one problem to finalize the app.

I've been trying to make two buttons on my main layout. The buttons are supposed to open a second layout, one called barcode_scanner.xml and another called vragen.xml

However, only the first button opens the scanner. The second button does not do anything.

This is my current code from MainActivity.java

package com.kvprasad.zbarbarcodescanner;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button scannerButton;

@Override
        //Barcodescanner knop
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Button next = (Button) findViewById(R.id.scannerButton);
            next.setOnClickListener(new View.OnClickListener() {
                public void onClick(View view) {
                    Intent myIntent = new Intent(view.getContext(), BarcodeScanner.class);
                    startActivityForResult(myIntent, 0);
                }
            });
        }




    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }








public class bovenbouw extends MainActivity{

    @Override
                public void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);
                    setContentView(R.layout.activity_main);
                    Button next = (Button) findViewById(R.id.bovenbutton);
                    next.setOnClickListener(new View.OnClickListener() {
                        public void onClick(View view) {
                            Intent myIntent = new Intent(view.getContext(), Vragen.class);
                            startActivityForResult(myIntent, 0);}});}}}

I don't see any problems in the code. What am I possibly doing wrong? Thank you.

Answer 1

Do not make multiple onCreate methods for the same activity. Handle all your button clicks in the same onCreate method. What you can do is this:

package com.kvprasad.zbarbarcodescanner;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

private Button scannerButton;

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@Override
//Barcodescanner knop
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button next1 = (Button) findViewById(R.id.scannerButton);
    next.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            Intent myIntent = new Intent(view.getContext(), BarcodeScanner.class);
            startActivityForResult(myIntent, 0);
        }
    });

    Button next2 = (Button) findViewById(R.id.bovenbutton);
    next.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            Intent myIntent = new Intent(view.getContext(), Vragen.class);
            startActivityForResult(myIntent, 0);}

        });
    }
}

Answer 2

You don't need 2 onCreate() methods for two buttons. As both of them are in the same layout, you can set onClickListener on both of them in one method only.

public class MainActivity extends AppCompatActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button next = (Button) findViewById(R.id.scannerButton);
        next.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                Intent myIntent = new Intent(this, BarcodeScanner.class);
                startActivityForResult(myIntent, 0);
            }
        });

        Button next1 = (Button) findViewById(R.id.bovenbutton);
        next.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                Intent myIntent = new Intent(this, Vragen.class);
                startActivityForResult(myIntent, 1); 
                //Make sure the second parameter is not 0, so that you can differentiate between them in onActivityReult method.
            }
        });
    }
}

Answer 3

You don't have to create another class for vragen.class after bovenbutton is pressed. just create another button for bovenbutton in the main class oncreate method besides the scanner_button

@Override
//Barcodescanner knop
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button next = (Button) findViewById(R.id.scannerButton);
    Button vragen = (Button) findViewById(R.id.bovenbutton);//button for vragen
    next.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            Intent myIntent = new Intent(view.getContext(), BarcodeScanner.class);
            startActivityForResult(myIntent, 0);
        }
    });
   //here goes the onclicklistener for vragen button
   vragen.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            Intent myIntent = new Intent(view.getContext(), Vragen.class);
            startActivityForResult(myIntent, 0);
        }
    });
}

Answer 4

You're not supposed to register two Activities in single .java file. You must create separate Activity.

Answer 5

package com.example.photosapp

import android.support.v7.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}