Problems with page transition

Asked

Viewed 165 times

-2

I’m trying to create a simple event to change page by clicking the button, but whenever I run the application it crashes when it opens.

Mainactivity:

package com.app.agrandesacada;

import android.support.v4.app.Fragment;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;

public class MainActivity extends Activity {
private Button btnAlunos;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btnAlunos=(Button)findViewById(R.id.btnaluno);

    btnAlunos.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
        Intent i = new Intent("com.app.agrandesacada.AlunoActivity");
        startActivity(i);
        finish();

        }
    });

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}


}

Manifestxml:

<?xml version="1.0" encoding="utf-8"?>


<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.app.agrandesacada.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="com.app.agrandesacada.AlunoActivity"
        android:label="@string/title_activity_aluno" >
        <intent-filter>
            <action android:name="com.app.agrandesacada.AlunoActivity" />

            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
</application>

Error:

04-29 20:45:51.941: D/androidruntime(511): Shutting down VM 04-29 20:45:51.941: W/dalvikvm(511): threadid=1: thread exiting with uncaught Exception (group=0x40015560) 04-29 20:45:51.961: E/androidruntime(511): FATAL EXCEPTION: main 04-29 20:45:51.961: E/Androidruntime(511): java.lang.Runtimeexception: Unable to start Activity Componentinfo{com.app.agrandesacada/com.app.agrandesacada.Mainactivity}: java.lang.Nullpointerexception 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread.performLaunchActivity(Activitythread.java:1647) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread.handleLaunchActivity(Activitythread.java:1663) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread.access$1500(Activitythread.java:117) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread$H.handleMessage(Activitythread.java:931) 04-29 20:45:51.961: E/Androidruntime(511): at android.os.Handler.dispatchMessage(Handler.java:99) 04-29 20:45:51.961: E/Androidruntime(511): at android.os.Looper.loop(Looper.java:123) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread.main(Activitythread.java:3683) 04-29 20:45:51.961: E/Androidruntime(511): at java.lang.reflect.Method.invokeNative(Native Method) 04-29 20:45:51.961: E/Androidruntime(511): at java.lang.reflect.Method.invoke(Method.java:507) 04-29 20:45:51.961: E/Androidruntime(511): at com.android.Internal.os.Zygoteinit$Methodandargscaller.run(Zygoteinit.java:839) 04-29 20:45:51.961: E/Androidruntime(511): at com.android.Internal.os.Zygoteinit.main(Zygoteinit.java:597) 04-29 20:45:51.961: E/Androidruntime(511): at Dalvik.system.Nativestart.main(Native Method) 04-29 20:45:51.961: E/Androidruntime(511): Caused by: java.lang.Nullpointerexception 04-29 20:45:51.961: E/Androidruntime(511): at com.app.agrandesacada.MainActivity.onCreate(Mainactivity.java:24) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 04-29 20:45:51.961: E/Androidruntime(511): at android.app.Activitythread.performLaunchActivity(Activitythread.java:1611) 04-29 20:45:51.961: E/Androidruntime(511): ... 11 more

He gives Nullpointexception but I don’t understand why.

java android
  • 2

    Give a debug and see where the execution really stops, because if the crash before the app runs it is very likely to be in the first lines.

  • 1

    Complementing the @Furflez comment, look to write methods onCreate onStart and onResume of Activity and put several log on them, to know how far the code can run.

2 answers

3

Install your Intent as follows:

Intent intent = new Intent(this, AlunoActivity.class);

  • Unfortunately it didn’t work, still with the same mistake yet :/

1

I was able to solve it, I was writing in xml Fragment and not in Activity so he was giving Nullpointerexception, because I couldn’t find the id btnaluno in xml Activity.

Browser other questions tagged java android

You are not signed in. Login or sign up in order to post.