When I try extending the View class to a subclass that will underline portions of the text drawn by ListView, 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 the Canvas of ListView items 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(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; 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 // by ListView is 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( 723): at android.widget.ListView.fillFromTop (ListView.java:664) E/AndroidRuntime( 723): at android.widget.ListView.layoutChildren (ListView.java:1481) E/AndroidRuntime( 723): at android.widget.AbsListView.onLayout (AbsListView.java:1113) E/AndroidRuntime( 723): at android.view.View.layout(View.java:6133) E/AndroidRuntime( 723): at android.widget.FrameLayout.onLayout (FrameLayout.java:333) E/AndroidRuntime( 723): at android.view.View.layout(View.java:6133) E/AndroidRuntime( 723): at android.widget.LinearLayout.setChildFrame (LinearLayout.java:1119) E/AndroidRuntime( 723): at android.widget.LinearLayout.layoutVertical (LinearLayout.java:998) E/AndroidRuntime( 723): at android.widget.LinearLayout.onLayout (LinearLayout.java:918) E/AndroidRuntime( 723): at android.view.View.layout(View.java:6133) E/AndroidRuntime( 723): at android.widget.FrameLayout.onLayout (FrameLayout.java:333) E/AndroidRuntime( 723): at android.view.View.layout(View.java:6133) E/AndroidRuntime( 723): at android.view.ViewRoot.performTraversals (ViewRoot.java:929) E/AndroidRuntime( 723): at android.view.ViewRoot.handleMessage (ViewRoot.java:1482) E/AndroidRuntime( 723): at android.os.Handler.dispatchMessage (Handler.java:99) E/AndroidRuntime( 723): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime( 723): at android.app.ActivityThread.main (ActivityThread.java:3948) E/AndroidRuntime( 723): at java.lang.reflect.Method.invokeNative (Native Method) E/AndroidRuntime( 723): at java.lang.reflect.Method.invoke (Method.java:521) E/AndroidRuntime( 723): at com.android.internal.os.ZygoteInit $MethodAndArgsCaller.run(ZygoteInit.java:782) E/AndroidRuntime( 723): at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:540) E/AndroidRuntime( 723): at dalvik.system.NativeStart.main(Native Method) I/Process ( 564): Sending signal. PID: 723 SIG: 3 - - - Initially I tried posting this question to the Android Beginners group (as I'm a Java novice), but got no responses. Anyone here have any suggestions? Thanks and best regards, Greg --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
