Ch. 4 MyView RuntimeException

jimw · July 27th, 2009, 09:45 PM

I'm interested in extending the View class to make a new UI class, much like the Ch. 4 MyView. So I'm trying to get MyView.java to work. But I keep getting a RuntimeException with few clues as to a solution, so I'd appreciate any advice.

I took the code snippet for the Ch. 4 MyView and created a simple Activity wrapper. Then I created a main.xml that should instantiate one MyView.

Here's the error:
----
Exception occurred: java.lang.RuntimeException (uncaught)"thread=<3> main", android.app.ActivityThread.performLaunchActivity() , line=2,141 bci=620
---
The problem seems seems to occur early; the jdb traceback is not obvious:

-------------
[1] android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2,141)
[2] android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2,157)
[3] android.app.ActivityThread.access$1800 (ActivityThread.java:112)
[4] android.app.ActivityThread$H.handleMessage (ActivityThread.java:1,581)
[5] android.os.Handler.dispatchMessage (Handler.java:88)
[6] android.os.Looper.loop (Looper.java:123)
[7] android.app.ActivityThread.main (ActivityThread.java:3,739)

java.lang.reflect.Method.invokeNative (native method)
[9] java.lang.reflect.Method.invoke (Method.java:515)
[10] com.android.internal.os.ZygoteInit$MethodAndArgsCa ller.run (ZygoteInit.java:739)
[11] com.android.internal.os.ZygoteInit.main (ZygoteInit.java:497)
[12] dalvik.system.NativeStart.main (native method)
--------------

There are basically three files for this application: MyView.java from the book, my wrapper MyViewActivity.java, and the layout main.xml. Here are the latter two:

-------------------------------- MyViewActivity.java

Code:

package com.jw.MyView;

import java.util.*;
import java.text.*;
import java.lang.*;
import android.app.*;
import android.widget.*;
import android.os.Bundle;

public class MyViewActivity extends Activity {

    private	MyView myView;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

	myView = (MyView) findViewById(R.id.myView);
    }

}

And here's main.xml:

-----------
{code]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/topLinLayout"
android:orientation="vertical">

<MyView android:id="@+id/myView">
</MyView>

</LinearLayout>
[/code]

sierawsk · July 27th, 2009, 11:09 PM

You didn't mention anything about your manifest file. You should post that also.

jimw · July 28th, 2009, 12:18 AM

I did forget the manifest file but here it is:

Code:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.jw.MyView"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MyViewActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
    <uses-sdk android:minSdkVersion="2" />
</manifest>

And here's strings.xml too:

Code:

<?xml version="1.0" encoding="utf-8"?>
<!-- $Id: strings.xml,v 1.7 2009/07/27 00:24:24 jim Exp $ -->

<resources>
  <string name="app_name">MyView</string>
  <string name="main_title">MyView Dev</string>
</resources>

sierawsk · July 28th, 2009, 11:14 AM

Ok, Jim. I think that your problem is inside your main.xml file. The MyView element isn't composed using the correct formats.

1) Since you created a custom View, I think you need to use the extended name of com.jw.MyView.MyView inside the XML.
2) Also, you need to add layout_width and layout_height rules. So the main.xml file should look like this:

Code:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

<com.jw.MyView.MyView 
    android:id="@+id/myView"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />

</LinearLayout>

Jeff S.

jimw · July 28th, 2009, 12:37 PM

Jeff, I am quite impressed that you were able to debug this code hands-off, and fingered both of my errors. I don't know how long it would have taken me to discover the fixes myself, but I know it would have been quite a while.

Hats off to you, and many thanks!

Jim