I am new to android development, experienced with Java. I am trying,
basically, to play around with OnClick events, using a button click to
change Layouts. I started by making two .xml files in my Layouts
folder of the project and just setting setContentView to the first xml
in onCreate and to the other xml in onClick. Through some searching I
found that another Activity and an Intent object. I tried this with
the following:
package org.Android.HelloAndroid;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class NextActivity extends Activity{
public void onCreate(Bundle bundle){
super.onCreate(bundle);
Button button = (Button) findViewById(R.id.goback);
button.setOnClickListener(new OnClickListener(){
public void onClick(View v){
Intent myIntent = new Intent(v.getContext(),
Hello_Android.class);
startActivityForResult(myIntent,0);
}
});
setContentView(R.layout.onclick);
}
}
package org.Android.HelloAndroid;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.*;
public class Hello_Android extends Activity{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle created) {
super.onCreate(created);
TextView tv = (TextView) findViewById(R.id.textview);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new OnClickListener(){
public void onClick(View v){
Intent myIntent = new
Intent(v.getContext(),NextActivity.class);
startActivityForResult(myIntent,0);
}
});
this.setContentView(R.layout.main);
}
}
When I run this I get the error:
"The application Hello_Android (process org.android.HelloAndroid) has
stopped unexpectedly. Please try again. Force Close."
I used logcat, which I will be the first to admit I am unfamiliar with
how to read, but what stood out was the java Stack trace,
E/AndroidRuntime( 180): Uncaught handler: thread main exiting due to
uncaught exception
E/AndroidRuntime( 180): java.lang.RuntimeException: Unable to start
activity ComponentInfo{org.Android.HelloAndroid/
org.Android.HelloAndroid.Hello_Android}:
java.lang.NullPointerException
E/AndroidRuntime( 180): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:
2496)
E/AndroidRuntime( 180): at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:
2512)
E/AndroidRuntime( 180): at android.app.ActivityThread.access
$2200(ActivityThread.java:119)
E/AndroidRuntime( 180): at android.app.ActivityThread
$H.handleMessage(ActivityThread.java:1863)
E/AndroidRuntime( 180): at
android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 180): at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 180): at
android.app.ActivityThread.main(ActivityThread.java:4363)
E/AndroidRuntime( 180): at
java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 180): at
java.lang.reflect.Method.invoke(Method.java:521)
E/AndroidRuntime( 180): at com.android.internal.os.ZygoteInit
$MethodAndArgsCaller.run(ZygoteInit.java:860)
E/AndroidRuntime( 180): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
E/AndroidRuntime( 180): at dalvik.system.NativeStart.main(Native
Method)
E/AndroidRuntime( 180): Caused by: java.lang.NullPointerException
E/AndroidRuntime( 180): at
org.Android.HelloAndroid.Hello_Android.onCreate(Hello_Android.java:17)
E/AndroidRuntime( 180): at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:
1047)
E/AndroidRuntime( 180): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:
2459)
What is the most interesting to me is the null pointer exception at
line 17 of Hello_Android.java, the line in question being:
button.setOnClickListener(new OnClickListener(){
I am not sure how this is throwing a null pointer exception though...
any help would be appreciated. Without the setOnClickListener call,
the application loads fine, the TextView and Button from my xml layout
file both appear.
--
You received this message because you are subscribed to the Google
Groups "Android Beginners" group.
NEW! Try asking and tagging your question on Stack Overflow at
http://stackoverflow.com/questions/tagged/android
To unsubscribe from this group, send email to
android-beginners+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/android-beginners?hl=en
