Android Button cannot find method in Activity

Question

I have a Android button that I have set the onClick attribute to the login() method in it's respective Activity. Here is the layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="io.github.james_parsons.fblafashionapp.LoginActivity">

    <EditText
        android:layout_width="300dp"
        android:layout_height="wrap_content"
        android:inputType="textEmailAddress"
        android:ems="10"
        android:id="@+id/email"
        android:hint="@string/email_hint"
        android:singleLine="true"
        android:layout_below="@+id/loginTitle"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="55dp"
        android:textColor="@color/text_secondary" />

    <Button
        android:layout_width="120dp"
        android:layout_height="wrap_content"
        android:text="@string/login_button_text"
        android:id="@+id/loginButton"
        android:background="@color/primary"
        android:layout_marginTop="55dp"
        android:layout_below="@+id/password"
        android:layout_centerHorizontal="true"
        android:elevation="2dp"
        android:onClick="login"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/login_title"
        android:id="@+id/loginTitle"
        android:textColor="@color/text_primary"
        android:textSize="28sp"
        android:gravity="center_vertical|center_horizontal"
        android:layout_alignParentTop="true"
        android:layout_alignParentEnd="true"
        android:layout_marginTop="10dp" />

    <EditText
        android:layout_width="300dp"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/password"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:hint="@string/password_hint"
        android:textColor="@color/text_secondary" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceSmall"
        android:id="@+id/error"
        android:layout_below="@+id/loginButton"
        android:layout_centerHorizontal="true"
        android:textColor="@color/error"
        android:layout_marginTop="30dp" />

</RelativeLayout>

Here is my Activity:

package io.github.james_parsons.fblafashionapp;

import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.view.Menu;
import android.view.MenuItem;

import com.parse.LogInCallback;
import com.parse.ParseException;
import com.parse.ParseUser;

public class LoginActivity extends Activity {

    public EditText email;
    public EditText password;

    public TextView error;

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

    @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_login, 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 void login() {
        email = (EditText) findViewById(R.id.email);
        password = (EditText) findViewById(R.id.password);
        error = (TextView) findViewById(R.id.error);

        ParseUser.logInInBackground(email.getText().toString(), password.getText().toString(), new LogInCallback() {
            @Override
            public void done(ParseUser user, ParseException e) {
                if (user != null) {
                    // Success
                } else {
                    error.setText("Error logging in. Please try again later.");
                }
            }
        });
    }
}

Here is my manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="io.github.james_parsons.fblafashionapp" >

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <application
        android:name=".Global"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".LoginActivity"
            android:label="@string/title_activity_login" >
        </activity>
    </application>

</manifest>

The exception looks like this:

09-25 11:42:04.533    2094-2094/io.github.james_parsons.fblafashionapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: io.github.james_parsons.fblafashionapp, PID: 2094
    java.lang.IllegalStateException: Could not find method login(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.widget.Button with id 'loginButton'
            at android.view.View$DeclaredOnClickListener.resolveMethod(View.java:4479)
            at android.view.View$DeclaredOnClickListener.onClick(View.java:4443)
            at android.view.View.performClick(View.java:5198)
            at android.view.View$PerformClick.run(View.java:21147)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:148)
            at android.app.ActivityThread.main(ActivityThread.java:5417)
            at java.lang.reflect.Method.invoke(Native Method)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Why can't Android find my method? The only method the layout can find is setListFooter from android.preference.PreferenceActivity.

Answer 1

In addition, the View parameter needs to be passed because the method is to be accessed by a view(Button). It would very well work without the parameter if the method is being called within another method.

Answer 2

Your login() method signature should contain View parameter.

    public void login(View view) {
    email = (EditText) findViewById(R.id.email);
    password = (EditText) findViewById(R.id.password);
    error = (TextView) findViewById(R.id.error);

    ParseUser.logInInBackground(email.getText().toString(), password.getText().toString(), new LogInCallback() {
        @Override
        public void done(ParseUser user, ParseException e) {
            if (user != null) {
                // Success
            } else {
                error.setText("Error logging in. Please try again later.");
            }
        }
    });
}

Answer 3

Your public void login() method has the wrong signature. It needs to take a View as a parameter.