[java] setContentView(R.layout.main); error

package com.elfapp;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener {

    private Button btn_Login;
    private EditText et_UserName;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        btn_Login = (Button) findViewById(R.id.button_login);
        btn_Login.setOnClickListener(this);

        et_UserName = (EditText) findViewById(R.id.editText_userName);
    }

    public void onClick(View v) {
        if (v.equals(btn_Login)) {
                // skriver ut en toast när man klickar på knappen
            Toast.makeText(MainActivity.this, "Ansluter till server...", Toast.LENGTH_SHORT).show();

                // används i debuggern för att påvisa att programmet exekverat hit
            Log.v("ThisApp", "onClick Successful");

                // TODO skickar det som står i et_UserName till controller (genom TCP/IP), som ska kolla om användaren finns
            // send et_UserName.getText().toString() to controller

                // if(username exists)
            Intent intent = new Intent(this, RoomActivity.class);
            this.startActivity(intent);
        }
    }

}

I'm getting an error on the line containing setContentView(R.layout.main); Not sure about what the error/exception is because I'm not used to working in Eclipse..

is this already solved?

i also had this problem. I solved it just by cleaning the project.

Project>Clean>Clean projects selected below>Check [your project's name]

Simply:

1. Right click on your project.

2. Go to properties.

3. Select android (second option in the Left panel).

4. Click "add..." (in library), select your project.

5. Click ok.

6. And finally, clean your project.

If this doesn't work, make sure that "android-support-v7-appcompat" is in your Project Explorer.

If it isn't there, you can add it by importing a simple project from: C:/android-sdks\extras\android\support\v7\appcompat

This just happend to me a minute ago, but after researching a while, and read this post I notice this.

There is a custom R class with you app name, so when you try to import the missing class (in Eclipse, press Ctrl + Shift + O to import missing classes (Cmd + Shift + O on Mac)), you should see two posible classes the normal:

import android.R;

And a custom class with your project namespace:

import com.yourname.yourapp.R;

If you choose the custom class, problem solved!

Step 1 : import android.*;

Step 2 : clean your project

Step 3 : Enjoy !!!

use code : setContentView(R.layout.activity_main); instead ofsetContentView(R.layout.main);

if you have multiple packages with different classes then it will be confusing: try this:

import package_name_from_AndroidManifest.R;

This problem usually happen if eclipse accidentally compile the main.xml incorrectly. The easiest solution is to delete R.java inside gen directory. Once we delete, than eclipse will generate the new R.java base on the latest main.xml

Using NetBeans 7.0:

If you fix imports before R.java has been generated for your project (before building it the first time) it will add the line:

import android.R;

which will override the local R.java that you are trying to reference.

Deleting that line resolved the errors for me.