Rookie error with OnClickListener

Question

Rookie error with OnClickListener

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#1 by (1 votes)
#2 by (0 votes)

1

I'm starting now in development for android. I'm trying to implement an onclicklistener on a button and it does not work at all, I've already followed step by step the video lessons from here, from youtube, and always from the error when compiling, what can it be? below is my java, xml, and logcat code:

Code

package com.example.treino;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

    Button button;
    TextView textView;

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

        button = (Button) findViewById(R.id.button1);
        textView = (TextView) findViewById(R.id.textView1);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText("wow!");
            }
        });
    }
}

XML

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.treino.MainActivity$PlaceholderFragment" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="59dp"
        android:text="Button" />

</RelativeLayout>

Log

05-26 19:22:33.703: D/AndroidRuntime(25773): Shutting down VM
05-26 19:22:33.703: W/dalvikvm(25773): threadid=1: thread exiting with uncaught exception (group=0x41f1dd40)
05-26 19:22:33.706: E/AndroidRuntime(25773): FATAL EXCEPTION: main
05-26 19:22:33.706: E/AndroidRuntime(25773): Process: com.example.treino, PID: 25773
05-26 19:22:33.706: E/AndroidRuntime(25773): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.treino/com.example.treino.MainActivity}: java.lang.NullPointerException
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread.access$800(ActivityThread.java:139)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.os.Handler.dispatchMessage(Handler.java:102)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.os.Looper.loop(Looper.java:136)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread.main(ActivityThread.java:5102)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at java.lang.reflect.Method.invokeNative(Native Method)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at java.lang.reflect.Method.invoke(Method.java:515)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at dalvik.system.NativeStart.main(Native Method)
05-26 19:22:33.706: E/AndroidRuntime(25773): Caused by: java.lang.NullPointerException
05-26 19:22:33.706: E/AndroidRuntime(25773):    at com.example.treino.MainActivity.onCreate(MainActivity.java:28)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.Activity.performCreate(Activity.java:5248)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
05-26 19:22:33.706: E/AndroidRuntime(25773):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
05-26 19:22:33.706: E/AndroidRuntime(25773):    ... 11 more
05-26 19:22:35.598: I/Process(25773): Sending signal. PID: 25773 SIG: 9
05-26 19:25:13.048: D/AndroidRuntime(26448): Shutting down VM
05-26 19:25:42.291: D/AndroidRuntime(26858): Shutting down VM
05-26 19:25:42.291: W/dalvikvm(26858): threadid=1: thread exiting with uncaught exception (group=0x41f1dd40)
05-26 19:25:42.294: E/AndroidRuntime(26858): FATAL EXCEPTION: main
05-26 19:25:42.294: E/AndroidRuntime(26858): Process: com.example.treino, PID: 26858
05-26 19:25:42.294: E/AndroidRuntime(26858): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.treino/com.example.treino.MainActivity}: java.lang.NullPointerException
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread.access$800(ActivityThread.java:139)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.os.Handler.dispatchMessage(Handler.java:102)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.os.Looper.loop(Looper.java:136)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread.main(ActivityThread.java:5102)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at java.lang.reflect.Method.invokeNative(Native Method)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at java.lang.reflect.Method.invoke(Method.java:515)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at dalvik.system.NativeStart.main(Native Method)
05-26 19:25:42.294: E/AndroidRuntime(26858): Caused by: java.lang.NullPointerException
05-26 19:25:42.294: E/AndroidRuntime(26858):    at com.example.treino.MainActivity.onCreate(MainActivity.java:23)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.Activity.performCreate(Activity.java:5248)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
05-26 19:25:42.294: E/AndroidRuntime(26858):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
05-26 19:25:42.294: E/AndroidRuntime(26858):    ... 11 more
05-26 19:25:43.807: I/Process(26858): Sending signal. PID: 26858 SIG: 9

java android

asked by anonymous 24.05.2014 / 03:26

2 answers

Problem importing new libraries to Java Use of Nested Attributes with relationship table "has_many through"

score 1 · Answer 1

1

Fixed

As Piovezan said, it was just switching activity_main to fragment_main in the method below:

setContentView(R.layout.activity_main);

27.05.2014 / 03:48

score 0 · Answer 2

I believe your NullPointerException error is in the line where you have this statement: Button button1 = (Button)findViewById(R.id.button1);

You probably forgot to declare a button in your xml file with the name button1 .

In this question link I explain about button . If you can solve your problem post here saying that you have succeeded.