我知道有很多人问过同样的事情，但我不知道发生了什么。我正在尝试制作像this这样的函数
它由2 EditText s，2 ListView和1个按钮组成。对于我的应用程序，用户将输入放在EditText内（1表示用户位置，另1表示目的地）我包含ListView的目的是当用户输入输入1或2个字母时，listView显示建议有关字母的地方。但是，ListView被隐藏 - 只有当用户将输入放入EditText时，它才会显示列表。
我的代码没有显示任何错误，但是当我运行logCat时给我这个：
07-02 15:57:39.160: E/AndroidRuntime(5545): FATAL EXCEPTION: main
07-02 15:57:39.160: E/AndroidRuntime(5545): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.series3/com.example.series3.FindMePlace}: java.lang.NullPointerException
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.os.Handler.dispatchMessage(Handler.java:99)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.os.Looper.loop(Looper.java:123)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread.main(ActivityThread.java:3683)
07-02 15:57:39.160: E/AndroidRuntime(5545): at java.lang.reflect.Method.invokeNative(Native Method)
07-02 15:57:39.160: E/AndroidRuntime(5545): at java.lang.reflect.Method.invoke(Method.java:507)
07-02 15:57:39.160: E/AndroidRuntime(5545): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-02 15:57:39.160: E/AndroidRuntime(5545): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-02 15:57:39.160: E/AndroidRuntime(5545): at dalvik.system.NativeStart.main(Native Method)
07-02 15:57:39.160: E/AndroidRuntime(5545): Caused by: java.lang.NullPointerException
07-02 15:57:39.160: E/AndroidRuntime(5545): at com.example.series3.FindMePlace.onCreate(FindMePlace.java:80)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
07-02 15:57:39.160: E/AndroidRuntime(5545): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
07-02 15:57:39.160: E/AndroidRuntime(5545): ... 11 more
认真地说我真的没有想法我错了。请帮我解决这个问题 这是我的代码：
FindMePlace.java
public class FindMePlace extends Activity {
// ------------------------------------------------------------------
// Declaration
public static UkmRoute selectedPath = null;
final DatabaseHandler db = new DatabaseHandler(this);
private EditText filterText = null;
private EditText filterText2 = null;
ArrayAdapter<String> adapter = null;
final ArrayList<String> results = new ArrayList<String>();
final ArrayList<String> results_id = new ArrayList<String>();
Button search;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.findmeplace);
// final Intent c = new Intent(FindMePlace.this,
// QSLocationDetail.class);
// ------------------------------------------------------------------
// Link editText to layout item
filterText = (EditText) findViewById(R.id.search_Location);
filterText.addTextChangedListener(filterTextWatcher);
filterText2 = (EditText) findViewById(R.id.search_Destination);
filterText2.addTextChangedListener(filterTextWatcher);
/*populateFromLocation();
populateToDestination();*/
// Reading location
Log.d("Reading", "Reading all location ..");
List<UkmRoute> location = db.getAllUKMRoute();
for (UkmRoute k : location) {
results.add(k.getFromLocation());
results_id.add(k.getID());
}
// Set list arrayAdapter to adapter
if (!filterText.getText().toString().equals(""))
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, results);
else {
ArrayList<String> r = new ArrayList<String>();
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, r);
}
// adapter = new ArrayAdapter<String>(this, R.layout.list_item,
// R.id.textView1, results);
setListAdapter(adapter);
// Set ListView from ListActivity
ListView lv = getListView();
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// When clicked, show a toast with the TextView text
Toast.makeText(getApplicationContext(),
((TextView) view).getText(), Toast.LENGTH_SHORT).show();
Log.d("test", "position:" + position);
Log.d("test",
"actualname:"
+ db.getUkmRouteByFrom(
adapter.getItem(position))
.getFromLocation());
// String poiID = results_id.get(position);
String poiID = db.getUkmRouteByFrom(adapter.getItem(position))
.getID();
setSelectedPoi(poiID);
// startActivity(c);
}
});
//-------------------------------------------------------------------------------
List<UkmRoute> destination = db.getAllUKMRoute();
for (UkmRoute k : destination) {
results.add(k.getToDestination());
results_id.add(k.getID());
}
if (!filterText2.getText().toString().equals(""))
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, results);
else {
ArrayList<String> r = new ArrayList<String>();
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, r);
}
setListAdapter(adapter);
// Set ListView from ListActivity
ListView lv2 = getListView();
lv2.setTextFilterEnabled(true);
// Set click event from listView
lv2.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// When clicked, show a toast with the TextView text
Toast.makeText(getApplicationContext(),
((TextView) view).getText(), Toast.LENGTH_SHORT).show();
Log.d("test", "position:" + position);
Log.d("test",
"actualname:"
+ db.getUkmRouteByTo(adapter.getItem(position))
.getFromLocation());
// String poiID = results_id.get(position);
String poiID = db.getUkmRouteByTo(adapter.getItem(position))
.getID();
setSelectedPoi(poiID);
// startActivity(c);
}
});
}
// Initiate database data
public void initiateDb() {
DatabaseHandler myDbHandler = new DatabaseHandler(this);
try {
myDbHandler.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHandler.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
Log.d("Initiate",
"UKM Route Count: " + myDbHandler.getUkmRouteCount());
myDbHandler.close();
}
// ------------------------------------------------------------------
private ListView getListView() {
// TODO Auto-generated method stub
return null;
}
private void setListAdapter(ArrayAdapter<String> adapter2) {
// TODO Auto-generated method stub
}
private TextWatcher filterTextWatcher = new TextWatcher() {
public void afterTextChanged(Editable s) {
}
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
}
public void onTextChanged(CharSequence s, int start, int before,
int count) {
if (!filterText.getText().toString().equals(""))
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, results);
else {
ArrayList<String> r = new ArrayList<String>();
adapter = new ArrayAdapter<String>(FindMePlace.this,
R.layout.list_item, R.id.textView1, r);
}
setListAdapter(adapter);
adapter.getFilter().filter(s);
}
};
@Override
protected void onDestroy() {
super.onDestroy();
filterText.removeTextChangedListener(filterTextWatcher);
}
public UkmRoute getSelectedPoi() {
return selectedPath;
}
public void setSelectedPoi(String ID_route) {
selectedPath = db.getUkmRoute(ID_route);
Log.d("test2", "ID_route:" + db.getUkmRoute(ID_route).getID());
Log.d("test2", "FromLocation:" + db.getUkmRoute(ID_route).getFromLocation());
// kene buat if else ke kalau nk tmbah part Destination?
// Closing db
db.close();
}
}
findmeplace.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".FindMePlace" >
<EditText
android:id="@+id/search_Destination"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/search_box"
android:layout_centerVertical="true"
android:ems="10"
android:hint="@string/edittext_hint1"
android:inputType="text"
android:maxLines="1" />
<EditText
android:id="@+id/search_Location"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="138dp"
android:ems="10"
android:hint="@string/edittext_hint"
android:inputType="text"
android:maxLines="1" >
<requestFocus />
</EditText>
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignRight="@+id/search_box"
android:layout_marginBottom="71dp"
android:text="@string/searchbutton" />
<ListView
android:id="@+id/inputLocation"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/search_Location"
android:layout_below="@+id/search_Location"
android:layout_marginLeft="32dp"
android:layout_marginTop="20dp" >
</ListView>
<ListView
android:id="@+id/inputDestination"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/search_Destination"
android:layout_below="@+id/search_Destination"
android:layout_marginTop="15dp" >
</ListView>
</RelativeLayout>
LIST_ITEM
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/textView1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dp"
android:textSize="16sp" >
</TextView>
答案 0 :(得分：1)
您的列表视图未初始化。
ListView lv = getListView(); // lv is null
http://developer.android.com/reference/android/app/ListActivity.html
ListActivity的默认布局包含屏幕中央的单个全屏列表。但是，如果需要，可以通过在onCreate（）中使用setContentView（）设置自己的视图布局来自定义屏幕布局。 为此，您自己的视图必须包含一个ID为“@android：id / list”的ListView对象（如果它在代码中则列出）
如果扩展ListActivity，您可以拥有单个列表视图。
<ListView
android:id="@android:id/list"
您的课程不会延长ListActivtiy。确保延长ListActivity
如果您延长Activity，则应执行以下操作
ListView lv = (ListView) findViewById(R.id.inputLocation);
lv.setAdapter(adapter);
你也有以下方法，什么都不做，应该删除。
private ListView getListView() {
// TODO Auto-generated method stub
return null;
}
private void setListAdapter(ArrayAdapter<String> adapter2) {
// TODO Auto-generated method stub
}
答案 1 :(得分：0)
您的getListView（）方法返回硬编码的null。在setTextFilterEnabled
下面的NPE一行答案 2 :(得分：0)
您尚未展开ListActivity，因此无法使用getListView() ..
如果您不延长id，则应ListActivity找到它。
如果您的列表的id等于list，则：
ListView lv = (ListView) findViewById(R.id.list);
顺便说一下，它可以有id ..
我认为ListActivity只限制了list ..我不喜欢这种行为。
但ListActivity有一些很好的方法可以使用列表，但我更喜欢Activity ...