我希望在用户在我的Android应用程序的屏幕布局顶部的搜索框中键入时过滤列表视图。为此，我使用textwatcher添加了一些代码并运行了我的应用程序，但现在它开始给出错误了它没有过滤列表。请帮我解决这个错误，并为我提供自动列表过滤搜索的完美代码.Thanx
logcat的：
03-05 20:51:34.560: E/log_tag(897): Error is:java.lang.ClassC
astException: android.widget.TextView
03-05 20:51:38.009: D/AndroidRuntime(897): Shutting down VM
03-05 20:51:38.009: W/dalvikvm(897): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
03-05 20:51:38.029: E/AndroidRuntime(897): FATAL EXCEPTION: main
03-05 20:51:38.029: E/AndroidRuntime(897): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.FirstProject/com.example.FirstProject.Trains}: java.lang.NullPointerException
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.os.Handler.dispatchMessage(Handler.java:99)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.os.Looper.loop(Looper.java:123)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread.main(ActivityThread.java:4627)
03-05 20:51:38.029: E/AndroidRuntime(897): at java.lang.reflect.Method.invokeNative(Native Method)
03-05 20:51:38.029: E/AndroidRuntime(897): at java.lang.reflect.Method.invoke(Method.java:521)
03-05 20:51:38.029: E/AndroidRuntime(897): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-05 20:51:38.029: E/AndroidRuntime(897): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-05 20:51:38.029: E/AndroidRuntime(897): at dalvik.system.NativeStart.main(Native Method)
03-05 20:51:38.029: E/AndroidRuntime(897): Caused by: java.lang.NullPointerException
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.Activity.findViewById(Activity.java:1637)
03-05 20:51:38.029: E/AndroidRuntime(897): at com.example.FirstProject.Trains. <init> (Trains.java:29)
03-05 20:51:38.029: E/AndroidRuntime(897): at java.lang.Class.newInstanceImpl(Native Method)
03-05 20:51:38.029: E/AndroidRuntime(897): at java.lang.Class.newInstance(Class.java:1429)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
03-05 20:51:38.029: E/AndroidRuntime(897): ... 11 more
java文件的代码：
package com.example.FirstProject;
import android.app.ListActivity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Filterable;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
public class City extends ListActivity{
protected ArrayAdapter adapter;
ListView lv;
Cursor cursor;
protected String[] cities = {"Mumbai","Nashik","Pune","Nagpur","Kolhapur","Aurangabad","Amravati"};
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.screen1);
try{
filterText = (EditText) findViewById(R.id.textView1);
filterText.addTextChangedListener(filterTextWatcher);
}
catch(Exception e)
{
Log.e("log_tag", "Error is:"+e.toString());
}
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, cities);
//ListView City = (ListView) findViewById(android.R.id.list);
setListAdapter(adapter);
}
private TextWatcher filterTextWatcher = new TextWatcher() {
@Override
public void afterTextChanged(Editable s) {
lv.setFilterText(s.toString());
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before,
int count) {
((Filterable) adapter).getFilter().filter(s);
}
};
private TextView filterText;
public void onListItemClick(ListView parent, View view, int position, long id) {
super.onListItemClick(parent, view, position, id);
switch(position)
{
case 0: Intent i = new Intent(this, Mumbai.class);
startActivity(i);
break;
}
}
@Override
protected void onDestroy() {
super.onDestroy();
filterText.removeTextChangedListener(filterTextWatcher);
}
}
xml文件的代码：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/City"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText android:id="@+building_list/search_box"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="type to filter"
android:inputType="text"
android:maxLines="1"/>
<ListView
android:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<!-- Preview: listitem=@android:layout/simple_list_item_1 -->
</ListView>
</LinearLayout>
答案 0 :(得分：2)
03-05 20:51:38.029: E/AndroidRuntime(897): Caused by: java.lang.NullPointerException
03-05 20:51:38.029: E/AndroidRuntime(897): at android.app.Activity.findViewById(Activity.java:1637)
03-05 20:51:38.029: E/AndroidRuntime(897): at com.example.FirstProject.Trains. <init> (Trains.java:29)
您正尝试从初始化程序中findViewById()拨打Activity。这不行。在之后 findViewById()之前，您无法致电setContentView()。
答案 1 :(得分：0)
TextView不是EditView。 （因此不能施放，因此抛出classcastexception）
在XML中，将textView1声明为EditText。