Thanks Jack,
Constraining the problem to a TextView rather than the whole row view
is a good idea, but the apparent cast problem has now moved to
holder.text = (MyUnderlinedTextView) convertView.findViewById
(R.id.text); And, changing the definition of the ViewHolder from
static class ViewHolder {
TextView text;
ImageView icon;
}
to
static class ViewHolder {
MyUnderlinedTextView text;
ImageView icon;
}
did not get rid of the apparent cast problem. Here's the current code
and stack trace. This evening I'll try changing the row's layout so
it references a MyUnderlinedTextView rather than a TextView. However
I was hoping that the seemingly simple addition of underlining
wouldn't require modification to the layout.
- - -
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.apis.view;
import android.app.ListActivity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.os.Bundle;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
/**
* Demonstrates how to write an efficient list adapter. The adapter
used in this example binds
* to an ImageView and to a TextView for each row in the list.
*
* To work efficiently the adapter implemented here uses two
techniques:
* - It reuses the convertView passed to getView() to avoid inflating
View when it is not necessary
* - It uses the ViewHolder pattern to avoid calling findViewById()
when it is not necessary
*
* The ViewHolder pattern consists in storing a data structure in the
tag of the view returned by
* getView(). This data structures contains references to the views we
want to bind data to, thus
* avoiding calls to findViewById() every time getView() is invoked.
*/
public class List14 extends ListActivity {
private static class MyUnderlinedTextView extends TextView {
public MyUnderlinedTextView(Context context) {
super(context);
}
public MyUnderlinedTextView(Context context, AttributeSet as) {
super(context, as);
}
public MyUnderlinedTextView(Context context, AttributeSet as,
int i)
{
super(context, as, i);
}
@Override
protected void onDraw(Canvas canvas){
super.onDraw(canvas);
// Would like to do some line drawing here (e.g., underlining
portions of text)
}
}
private static class EfficientAdapter extends BaseAdapter {
private LayoutInflater mInflater;
private Bitmap mIcon1;
private Bitmap mIcon2;
public EfficientAdapter(Context context) {
// Cache the LayoutInflate to avoid asking for a new one
each time.
mInflater = LayoutInflater.from(context);
// Icons bound to the rows.
mIcon1 = BitmapFactory.decodeResource(context.getResources
(), R.drawable.icon48x48_1);
mIcon2 = BitmapFactory.decodeResource(context.getResources
(), R.drawable.icon48x48_2);
}
/**
* The number of items in the list is determined by the number
of speeches
* in our array.
*
* @see android.widget.ListAdapter#getCount()
*/
public int getCount() {
return DATA.length;
}
/**
* Since the data comes from an array, just returning the
index is
* sufficent to get at the data. If we were using a more
complex data
* structure, we would return whatever object represents one
row in the
* list.
*
* @see android.widget.ListAdapter#getItem(int)
*/
public Object getItem(int position) {
return position;
}
/**
* Use the array index as a unique id.
*
* @see android.widget.ListAdapter#getItemId(int)
*/
public long getItemId(int position) {
return position;
}
/**
* Make a view to hold each row.
*
* @see android.widget.ListAdapter#getView(int,
android.view.View,
* android.view.ViewGroup)
*/
public View getView(int position, View convertView, ViewGroup
parent) {
// A ViewHolder keeps references to children views to
avoid unneccessary calls
// to findViewById() on each row.
ViewHolder holder;
// When convertView is not null, we can reuse it directly,
there is no need
// to reinflate it. We only inflate a new View when the
convertView supplied
// by ListView is null.
if (convertView == null) {
convertView = mInflater.inflate
(R.layout.list_item_icon_text, null);
// Creates a ViewHolder and store references to the
two children views
// we want to bind data to.
holder = new ViewHolder();
holder.text = (MyUnderlinedTextView)
convertView.findViewById(R.id.text);
holder.icon = (ImageView) convertView.findViewById
(R.id.icon);
convertView.setTag(holder);
} else {
// Get the ViewHolder back to get fast access to the
TextView
// and the ImageView.
holder = (ViewHolder) convertView.getTag();
}
// Bind the data efficiently with the holder.
holder.text.setText(DATA[position]);
holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 :
mIcon2);
return convertView;
}
static class ViewHolder {
MyUnderlinedTextView text;
ImageView icon;
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setListAdapter(new EfficientAdapter(this));
}
private static final String[] DATA = {
"Abbaye de Belloc", "Abbaye du Mont des Cats", "Abertam",
"Abondance", "Ackawi", "Acorn", "Adelost", "Affidelice au
Chablis",
"Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre",
" ... ",
"Zanetti Grana Padano", "Zanetti Parmigiano Reggiano"};
}
- - -
D/AndroidRuntime( 721): Shutting down VM
W/dalvikvm( 721): threadid=3: thread exiting with uncaught exception
(group=0x4000fe70)
E/AndroidRuntime( 721): Uncaught handler: thread main exiting due to
uncaught exception
E/AndroidRuntime( 721): java.lang.ClassCastException:
android.widget.TextView
E/AndroidRuntime( 721): at
com.example.android.apis.view.List14$EfficientAdapter.getView
(List14.java:130)
E/AndroidRuntime( 721): at android.widget.AbsListView.obtainView
(AbsListView.java:1269)
E/AndroidRuntime( 721): at android.widget.ListView.makeAndAddView
(ListView.java:1623)
E/AndroidRuntime( 721): at android.widget.ListView.fillDown
(ListView.java:607)
E/AndroidRuntime( 721): at android.widget.ListView.fillFromTop
(ListView.java:664)
E/AndroidRuntime( 721): at android.widget.ListView.layoutChildren
(ListView.java:1481)
E/AndroidRuntime( 721): at android.widget.AbsListView.onLayout
(AbsListView.java:1113)
E/AndroidRuntime( 721): at android.view.View.layout(View.java:6133)
E/AndroidRuntime( 721): at android.widget.FrameLayout.onLayout
(FrameLayout.java:333)
E/AndroidRuntime( 721): at android.view.View.layout(View.java:6133)
E/AndroidRuntime( 721): at android.widget.LinearLayout.setChildFrame
(LinearLayout.java:1119)
E/AndroidRuntime( 721): at android.widget.LinearLayout.layoutVertical
(LinearLayout.java:998)
E/AndroidRuntime( 721): at android.widget.LinearLayout.onLayout
(LinearLayout.java:918)
E/AndroidRuntime( 721): at android.view.View.layout(View.java:6133)
E/AndroidRuntime( 721): at android.widget.FrameLayout.onLayout
(FrameLayout.java:333)
E/AndroidRuntime( 721): at android.view.View.layout(View.java:6133)
E/AndroidRuntime( 721): at android.view.ViewRoot.performTraversals
(ViewRoot.java:929)
E/AndroidRuntime( 721): at android.view.ViewRoot.handleMessage
(ViewRoot.java:1482)
E/AndroidRuntime( 721): at android.os.Handler.dispatchMessage
(Handler.java:99)
E/AndroidRuntime( 721): at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 721): at android.app.ActivityThread.main
(ActivityThread.java:3948)
E/AndroidRuntime( 721): at java.lang.reflect.Method.invokeNative
(Native Method)
E/AndroidRuntime( 721): at java.lang.reflect.Method.invoke
(Method.java:521)
E/AndroidRuntime( 721): at com.android.internal.os.ZygoteInit
$MethodAndArgsCaller.run(ZygoteInit.java:782)
E/AndroidRuntime( 721): at com.android.internal.os.ZygoteInit.main
(ZygoteInit.java:540)
E/AndroidRuntime( 721): at dalvik.system.NativeStart.main(Native
Method)
I/Process ( 564): Sending signal. PID: 721 SIG: 3
- - -
Thanks again and best regards,
Greg
On Jul 29, 11:55 am, Jack Ha <[email protected]> wrote:
> Don't do this:
>
> UnderlinedView underlinedView = (UnderlinedView) convertView;
>
> Instead create your own MyUnderlinedTextView class by extending
> TextView.
>
> holder.text = (MyUnderlinedTextView) convertView.findViewById
> (R.id.text);
>
> --
> Jack Ha
> Open Source Development Center
> ・T・ ・ ・Mobile・ stick together
>
> The views, opinions and statements in this email are those of
> the author solely in their individual capacity, and do not
> necessarily represent those of T-Mobile USA, Inc.
>
> On Jul 28, 7:54 pm, greg <[email protected]> wrote:
>
> > When I try extending the View class to a subclass that will underline
> > portions of the text drawn byListView, the code compiles okay but
> > results in a runtime exception apparently due to an improper class
> > cast. Does anyone see what I've done wrong or have suggestions about
> > getting access to theCanvasofListViewitems so portions of text can
> > be underlined?
>
> > Here is the code, which is the Efficient Adapter View/List example
> > from ApiDemos with an added UnderlinedView class.
>
> > - - -
>
> > /*
> > * Copyright (C) 2008 The Android Open Source Project
> > *
> > * Licensed under the Apache License, Version 2.0 (the "License");
> > * you may not use this file except in compliance with the License.
> > * You may obtain a copy of the License at
> > *
> > * http://www.apache.org/licenses/LICENSE-2.0
> > *
> > * Unless required by applicable law or agreed to in writing, software
> > * distributed under the License is distributed on an "AS IS" BASIS,
> > * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
> > implied.
> > * See the License for the specific language governing permissions and
> > * limitations under the License.
> > */
>
> > package com.example.android.apis.view;
>
> > import android.app.ListActivity;
> > import android.content.Context;
> > import android.graphics.Bitmap;
> > import android.graphics.BitmapFactory;
> > import android.graphics.Canvas;
> > import android.os.Bundle;
> > import android.util.AttributeSet;
> > import android.view.LayoutInflater;
> > import android.view.View;
> > import android.view.ViewGroup;
> > import android.widget.BaseAdapter;
> > import android.widget.ImageView;
> > import android.widget.TextView;
>
> > /**
> > * Demonstrates how to write an efficient list adapter. The adapter
> > used in this example binds
> > * to an ImageView and to a TextView for each row in the list.
> > *
> > * To work efficiently the adapter implemented here uses two
> > techniques:
> > * - It reuses the convertView passed to getView() to avoid inflating
> > View when it is not necessary
> > * - It uses the ViewHolder pattern to avoid calling findViewById()
> > when it is not necessary
> > *
> > * The ViewHolder pattern consists in storing a data structure in the
> > tag of the view returned by
> > * getView(). This data structures contains references to the views we
> > want to bind data to, thus
> > * avoiding calls to findViewById() every time getView() is invoked.
> > */
> > public class List14 extends ListActivity {
>
> > private static class UnderlinedView extends View {
> > public UnderlinedView(Context context) {
> > super(context);
> > }
> > public UnderlinedView(Context context, AttributeSet as) {
> > super(context, as);
> > }
> > public UnderlinedView(Context context, AttributeSet as, int
> > i) {
> > super(context, as, i);
> > }
> > @Override
> > protected void onDraw(Canvascanvas) {
> > super.onDraw(canvas);
>
> > // Would like to do some line drawing here (e.g.,
> > underlining
> > portions of text)
> > }
> > }
>
> > private static class EfficientAdapter extends BaseAdapter {
> > private LayoutInflater mInflater;
> > private Bitmap mIcon1;
> > private Bitmap mIcon2;
>
> > public EfficientAdapter(Context context) {
> > // Cache the LayoutInflate to avoid asking for a new one
> > each time.
> > mInflater = LayoutInflater.from(context);
>
> > // Icons bound to the rows.
> > mIcon1 = BitmapFactory.decodeResource(context.getResources
> > (), R.drawable.icon48x48_1);
> > mIcon2 = BitmapFactory.decodeResource(context.getResources
> > (), R.drawable.icon48x48_2);
> > }
>
> > /**
> > * The number of items in the list is determined by the number
> > of speeches
> > * in our array.
> > *
> > * @see android.widget.ListAdapter#getCount()
> > */
> > public int getCount() {
> > return DATA.length;
> > }
>
> > /**
> > * Since the data comes from an array, just returning the
> > index is
> > * sufficent to get at the data. If we were using a more
> > complex data
> > * structure, we would return whatever object represents one
> > row in the
> > * list.
> > *
> > * @see android.widget.ListAdapter#getItem(int)
> > */
> > public Object getItem(int position) {
> > return position;
> > }
>
> > /**
> > * Use the array index as a unique id.
> > *
> > * @see android.widget.ListAdapter#getItemId(int)
> > */
> > public long getItemId(int position) {
> > return position;
> > }
>
> > /**
> > * Make a view to hold each row.
> > *
> > * @see android.widget.ListAdapter#getView(int,
> > android.view.View,
> > * android.view.ViewGroup)
> > */
> > public View getView(int position, View convertView, ViewGroup
> > parent) {
> > // A ViewHolder keeps references to children views to
> > avoid unneccessary calls
> > // to findViewById() on each row.
> > ViewHolder holder;
> > UnderlinedView underlinedView = (UnderlinedView)
> > convertView;
>
> > // When convertView is not null, we can reuse it directly,
> > there is no need
> > // to reinflate it. We only inflate a new View when the
> > convertView supplied
> > // byListViewis null.
> > if (convertView == null) {
> > convertView = mInflater.inflate
> > (R.layout.list_item_icon_text, null);
> > underlinedView = (UnderlinedView)convertView;
>
> > // Creates a ViewHolder and store references to the
> > two children views
> > // we want to bind data to.
> > holder = new ViewHolder();
> > holder.text = (TextView) underlinedView.findViewById
> > (R.id.text);
> > holder.icon = (ImageView) underlinedView.findViewById
> > (R.id.icon);
>
> > underlinedView.setTag(holder);
> > } else {
> > // Get the ViewHolder back to get fast access to the
> > TextView
> > // and the ImageView.
> > holder = (ViewHolder) underlinedView.getTag();
> > }
>
> > // Bind the data efficiently with the holder.
> > holder.text.setText(DATA[position]);
> > holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 :
> > mIcon2);
>
> > return underlinedView;
> > }
>
> > static class ViewHolder {
> > TextView text;
> > ImageView icon;
> > }
> > }
>
> > @Override
> > public void onCreate(Bundle savedInstanceState) {
> > super.onCreate(savedInstanceState);
> > setListAdapter(new EfficientAdapter(this));
> > }
>
> > private static final String[] DATA = {
> > "Abbaye de Belloc", "Abbaye du Mont des Cats", "Abertam",
> > "Abondance", "Ackawi", "Acorn", "Adelost", "Affidelice au
> > Chablis",
> > "Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre",
> > "... a lot more strings are defined in original ApiDemos
> > sample ...",
> > "Yarra Valley Pyramid", "Yorkshire Blue", "Zamorano",
> > "Zanetti Grana Padano", "Zanetti Parmigiano Reggiano"};
>
> > }
>
> > - - -
>
> > The stack trace from logcat suggests a problem with the class cast in
> > line 127, which is the cast after the row's XML inflation in getView:
>
> > convertView = mInflater.inflate
> > (R.layout.list_item_icon_text, null);
> > underlinedView = (UnderlinedView)convertView;
>
> > D/AndroidRuntime( 723): Shutting down VM
>
> > W/dalvikvm( 723): threadid=3: thread exiting with uncaught exception
> > (group=0x4000fe70)
>
> > E/AndroidRuntime( 723): Uncaught handler: thread main exiting due to
> > uncaught exception
>
> > E/AndroidRuntime( 723): java.lang.ClassCastException:
> > android.widget.LinearLayout
>
> > E/AndroidRuntime( 723): at
> > com.example.android.apis.view.List14$EfficientAdapter.getView
> > (List14.java:127)
>
> > E/AndroidRuntime( 723): at android.widget.AbsListView.obtainView
> > (AbsListView.java:1269)
>
> > E/AndroidRuntime( 723): at android.widget.ListView.makeAndAddView
> > (ListView.java:1623)
>
> > E/AndroidRuntime( 723): at android.widget.ListView.fillDown
> > (ListView.java:607)
>
> > E/AndroidRuntime(
>
> ...
>
> read more »
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