Hi all,
I am rather new to Android programming in general and am having
particular difficulty with the xml/java UI shuffle... I have a layout
which I would like to use as the view displayed when a custom, view
class is instantiated in the activity class. This much works fine by
simply calling
setContentView(R.layout.mylayout) ;
in the activity or from the custom view class through a handle to the
activity. The trouble comes when I wish to interact with the widgets
on the layout-- I've tried getting a handle on the buttons with
myButton = (Button) findViewById(R.id.mybuttonid);
and separately with
Button myButton = new Button(contextHandle);
myButton = (Button) findViewById(R.layout.mybuttonid);
but in both cases whenever I try to call any methods from the assumed
myButton object I get a NullPointerException in the logcat report;
evidently myButton is not properly instantiated in either case given
above. What is the proper way to instantiate components of a view in a
case like this that combines xml and java so that they can call
methods dynamically?
Below is my code--
MyActivity Class:
<code>
package com.ccg.myactivity;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
public class MyActivity extends Activity implements
OnClickListener {
private boolean touched = false;
private RadioButton myRB;
private Button runB;
private CustomView myView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mainlayout);
myRB = (RadioButton) findViewById(R.id.testrb);
runB = (Button) findViewById(R.id.goButton);
//set onClick listeners for activity class
runB.setOnClickListener(this);
}
public void onResume(){
super.onResume();
}
public void onClick(View v) {
// do something when the button is clicked
if (myRB.isChecked()){
setContentView(R.layout.mylayout);
myView = new CustomView(this,this); //passing in activity
and context
//handles to custom View class
//myView.getAnotherB().setOnClickListener(this); //
commented out as we
//don't want to register the custom view's button with the Activty
class's
//OnClickListener; instead it should be registered with the custom
View class's own
//OnClickListener implementation.
}
else{
Log.d("me","alt click");
}
}
}</code>
CustomView Class:
<code>
package com.ccg.myactivity;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.*;
import android.view.View.OnClickListener;
public class CustomView extends View implements OnClickListener{
private Button anotherB;
private Context contextHandle;
private Activity actHandle;
public CustomView(Context context, Activity act) {
super(context);
contextHandle = context;
actHandle = act;
//anotherB = new Button(contextHandle); //this shouldn't be
necessary for
//instantiation from XML widget
initCustomView();
}
public void initCustomView(){
anotherB = (Button) findViewById(R.id.nextbutton);
anotherB.setOnClickListener(this);
}
public Button getAnotherB(){
return anotherB;
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.d("me", "Got the custom click!");
}
}</code>
mainlayout.xml from which the default view is made:
<code>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="@+id/widget474"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android";
android:orientation="vertical">
<RadioGroup android:id="@+id/widget30"
android:orientation="horizontal"
android:layout_x="2dip" android:layout_y="57dip"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<RadioButton android:layout_height="wrap_content" android:id="@+id/
testrb"
android:textSize="15sp" android:text="Run"
android:layout_width="wrap_content"
android:textColor="#ffff99ff"></RadioButton>
</RadioGroup>
<Button android:layout_width="wrap_content" android:text="@string/
RUN"
android:id="@+id/goButton" android:layout_height="wrap_content"
android:layout_x="222dip" android:layout_y="110dip"></Button>
</LinearLayout>
</code>
mylayout.xml from which the custom view's layout is created:
<code>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="@+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android";
android:orientation="vertical">
<Button android:id="@+id/nextbutton"
android:layout_height="wrap_content"
android:layout_width="wrap_content" android:text="work!!!"
>
</Button>
</LinearLayout>
</code>
okay, if anybody can explain why any method calls from the button
object anotherB (anotherB.setOnClickListener(this) above, but also the
simpler anotherB.bringToFront()) cause a force close and a
nullpointerexception in logcat with the above implementation I would
be most appreciative.
thanks!
CCJ
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