My app crashes when I use the OnClicklistener for a button even when it's empty
My activity is this: it is a LogInActivity that uses a layout with the same name, when I add activity listeners for buttons, the app crashes please help me this is from the last two days.
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.view.View.OnClickListener;
import java.io.Serializable;
public class LogInActivity extends ActionBarActivity {
private Button signUpButton;
private Button logInButton;
private Intent signUpChoiceIntent;
private OnClickListener signupListener;
private HumLogController humLogController;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setIntentAndButton();
setContentView(R.layout.activity_log_in);
}
private void setIntentAndButton(){
signUpChoiceIntent = new Intent (this , SignUpChoiceActivity.class);
signUpButton = (Button) findViewById(R.id.firstSignupButton);
logInButton = (Button) findViewById(R.id.firstLoginButton);
signupListener = new OnClickListener() {
@Override
public void onClick(View v) {
}
};
signUpButton.setOnClickListener(signupListener);
}
}
Layout file, two buttons create the whole problem:
<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=".LogInActivity"
android:background="#ff0aff62"
android:id="@+id/logInRelativeLayout">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/logInUsernameField"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="126dp"
android:textSize="30sp"
android:background="#ffffffff"
android:hint="@string/username_field_hint_text"
android:lines="1"
android:singleLine="true"
android:maxLength="40" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:id="@+id/logInPasswordField"
android:hint="@string/password_field_hint_text"
android:textSize="30sp"
android:background="#ffffffff"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"
android:layout_marginTop="176dp"
android:lines="1"
android:singleLine="true"
android:maxLength="15" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/sign_in_button_text"
android:id="@+id/firstLoginButton"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"
android:layout_marginTop="226dp"
android:background="#fff54d70"
android:textSize="30sp"
android:textColor="#ffffffff" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/sign_up_button_text"
android:id="@+id/firstSignupButton"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginTop="376dp"
android:textSize="30sp"
android:background="#ff0aff62"
android:textColor="#ff000000"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/or_text"
android:id="@+id/textView"
android:textSize="30sp"
android:layout_below="@+id/firstLoginButton"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_marginTop="306dp"
android:layout_marginLeft="136dp"
android:layout_marginStart="136dp"/>
//I am not missing the /relative layout closing tag, it is just not here
And this is the stack trace:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.praduman.humlog/com.example.praduman.humlog.LogInActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.access$600(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.praduman.humlog.LogInActivity.setIntentAndButton(LogInActivity.java:41)
at com.example.praduman.humlog.LogInActivity.onCreate(LogInActivity.java:26)
at android.app.Activity.performCreate(Activity.java:5133)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.access$600(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
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3 answers
Try the following:
public class LogInActivity extends ActionBarActivity {
private Button signUpButton;
private Button logInButton;
private Intent signUpChoiceIntent;
private OnClickListener signupListener;
private HumLogController humLogController;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_log_in);
setIntentAndButton();
}
private void setIntentAndButton(){
signUpChoiceIntent = new Intent (this , SignUpChoiceActivity.class);
signUpButton = (Button) findViewById(R.id.firstSignupButton);
logInButton = (Button) findViewById(R.id.firstLoginButton);
signupListener = new OnClickListener() {
@Override
public void onClick(View v) {
System.out.println("clicked");
}
};
signUpButton.setOnClickListener(signupListener);
}
}
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protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setIntentAndButton();
setContentView(R.layout.activity_log_in);
}
Should be:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_log_in);
setIntentAndButton();
}
The reason is that if you don't set the content view resource, all findViewByID methods will return null.
You can also shorten this:
signupListener = new OnClickListener() {
@Override
public void onClick(View v) {
}
};
signUpButton.setOnClickListener(signupListener);
:
signUpButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
}
};
);
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You call setIntentAndButton()
- where you connect the listeners - before you call setContentView()
. This way, the buttons weren't created when you try to attach listeners, but the calls findViewById
will not return null
. You need to create your view before trying to manipulate objects with it.
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_log_in);
setIntentAndButton();
}
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