我是Android编程的新手。我想创建一个搜索活动，这确实是我无法实现的。以下是java代码，xml代码和我的logCat。 Logcat总是要求“强制关闭”。我正在android 2.2上构建这个应用程序。请帮忙。
这是searchActivity.java代码：
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jsonParser = new JSONParser();
ArrayList<HashMap<String, String>> schemeList;
private ListView lv;
// products JSONArray
JSONArray scheme_array = null;
EditText inputSearch;
ArrayAdapter<HashMap<String, String>> adapter;
// Inbox JSON url
private static final String INBOX_URL = "http://115.240.97.85/Schemes_NAV/schemes.json";
// ALL JSON node names
private static final String TAG_SCHEME = "scheme";
private static final String TAG_ID = "id";
private static final String TAG_FROM = "id_from";
private static final String TAG_SUBJECT = "subject";
private static final String TAG_LASTPRICE = "last_price";
private static final String TAG_CHANGE = "change";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mf_search);
// Hashmap for ListView
schemeList = new ArrayList<HashMap<String, String>>();
// Loading INBOX in Background Thread
new LoadInbox().execute();
ListView lv = (ListView)findViewById(R.id.mfList); // create a list view
inputSearch = (EditText) findViewById(R.id.EditText01);
adapter = new ArrayAdapter<HashMap<String, String>>(this, R.layout.mf_search, schemeList);
lv.setAdapter(adapter);
inputSearch.addTextChangedListener(new TextWatcher() {
@Override
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
// When user changed the Text
searchActivity.this.adapter.getFilter().filter(cs);
}
@Override
public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
int arg3) {
// TODO Auto-generated method stub
}
@Override
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
}
});
}
/**
* Background Async Task to Load all INBOX messages by making HTTP Request
* */
class LoadInbox extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(searchActivity.this);
pDialog.setMessage("Loading Schemes ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting Inbox JSON
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jsonParser.makeHttpRequest(INBOX_URL, "GET",
params);
// Check your log cat for JSON response
Log.d("Scheme JSON: ", json.toString());
try {
scheme_array= json.getJSONArray(TAG_SCHEME);
// looping through All messages
for (int i = 0; i < scheme_array.length(); i++) {
JSONObject c = scheme_array.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_ID);
String id_from = c.getString(TAG_FROM);
String subject = c.getString(TAG_SUBJECT);
String lastprice = c.getString(TAG_LASTPRICE);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_ID, id);
map.put(TAG_FROM, id_from);
map.put(TAG_SUBJECT, subject);
map.put(TAG_LASTPRICE, lastprice);
// adding HashList to ArrayList
schemeList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
searchActivity.this, schemeList,
R.layout.inbox_list_item, new String[] { TAG_FROM},
new int[] { R.id.from });
// updating listview
setListAdapter(adapter);
}
});
}
}}
以下显示xml，即inbox_list_item.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/from"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:paddingBottom="4dip"
android:paddingLeft="8dip"
android:paddingTop="8dip"
android:textColor="@android:color/white"
android:textSize="20dip"
/>
<CheckBox
android:id="@+id/CheckBox01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginRight="16dp"
android:clickable="true" />
这是我的mf_search.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/a"
android:orientation="vertical" >
<EditText
android:id="@+id/EditText01"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="@string/Search" >
</EditText>
<ListView
android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="378dp"
android:layout_weight="925.26"
android:clickable="true" >
</ListView>
<Button
android:id="@+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Add" />
这是我的LogCat
03-10 02:14:16.637: D/dalvikvm(569): GC_EXTERNAL_ALLOC freed 720 objects / 53960 bytes in 153ms
03-10 02:14:24.728: D/dalvikvm(569): GC_EXTERNAL_ALLOC freed 486 objects / 26136 bytes in 93ms
03-10 02:14:25.868: D/AndroidRuntime(569): Shutting down VM
03-10 02:14:25.868: W/dalvikvm(569): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
03-10 02:14:25.917: E/AndroidRuntime(569): FATAL EXCEPTION: main
03-10 02:14:25.917: E/AndroidRuntime(569): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nav2/com.example.nav2.searchActivity}: java.lang.NullPointerException
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.os.Handler.dispatchMessage(Handler.java:99)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.os.Looper.loop(Looper.java:123)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread.main(ActivityThread.java:4627)
03-10 02:14:25.917: E/AndroidRuntime(569): at java.lang.reflect.Method.invokeNative(Native Method)
03-10 02:14:25.917: E/AndroidRuntime(569): at java.lang.reflect.Method.invoke(Method.java:521)
03-10 02:14:25.917: E/AndroidRuntime(569): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-10 02:14:25.917: E/AndroidRuntime(569): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-10 02:14:25.917: E/AndroidRuntime(569): at dalvik.system.NativeStart.main(Native Method)
03-10 02:14:25.917: E/AndroidRuntime(569): Caused by: java.lang.NullPointerException
03-10 02:14:25.917: E/AndroidRuntime(569): at com.example.nav2.searchActivity.onCreate(searchActivity.java:82)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-10 02:14:25.917: E/AndroidRuntime(569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
03-10 02:14:25.917: E/AndroidRuntime(569): ... 11 more
03-10 02:14:30.177: I/Process(569): Sending signal. PID: 569 SIG: 9
答案 0 :(得分：1)
使用
ListView lv = (ListView) findViewById(android.R.id.list);
或
ListView lv=this.getListView();
而不是
ListView lv = (ListView)findViewById(R.id.mfList);
因为你在xml中有ListView标识android:id="@android:id/list"但是试图找到R.id.mfList
答案 1 :(得分：0)
使用ListView lv = (ListView) findViewById(android.R.id.list)，您可以在XML中看到您的列表ID为android:id="@android:id/list，但您的目标ListView lv = (ListView)findViewById(R.id.mfList)不存在