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當我有這樣的Android - getListView和setListAdapter與NullPointerException異常錯誤使用自定義佈局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff">
<com.ftni.core.ui.ActionBar
android:id="@+id/actionbar"
style="@style/ActionBar"/>
<TextView android:id="@+id/list_title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Title"
android:textStyle="bold"
android:textColor="#000000"
android:textSize="18sp"
android:padding="3px"/>
<ListView android:id="@id/android:list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:drawSelectorOnTop="false"/>
</LinearLayout>
，並在我的列表視圖（代碼之前，我改變了佈局正在）
private void buildListView()
{
ListView lv = getListView();
registerForContextMenu(lv);
lv.setTextFilterEnabled(true);
lv.clearChoices();
setListAdapter(new UserListAdapter(SuspendedUsersActivity.this, R.layout.useritem, users));
lv.setOnItemClickListener(clickListener);
}
佈局我試着先將呼叫移至setListAdapter，但我仍然得到NullPointerException。這裏的logcat的
FATAL EXCEPTION: main
java.lang.NullPointerException
at android.app.ListActivity.setListAdapter(ListActivity.java:267)
at com.myapp.backoffice.users.SuspendedUsersActivity.buildListView(SuspendedUsersActivity.java:140)
at com.myapp.backoffice.users.SuspendedUsersActivity.access$0(SuspendedUsersActivity.java:138)
at com.myapp.backoffice.users.SuspendedUsersActivity$2.handleMessage(SuspendedUsersActivity.java:194)
at android.os.Handler.dispatchMessage(Handler.java:99)
我有一種感覺，正在發生的事情是，我被告知默認ID是正確的（@id/android:list）不是默認的列表視圖正確的。
編輯：
下面是關於我如何設置的更多細節。
首先，我有一個繼承的活動，以確保用戶通過身份驗證。當我直接從這個類繼承時，一切正常。
public class ProtectedListActivity extends ListActivityBase {
boolean isAuthenticated = false;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Thread validationThread = new Thread()
{
@Override
public void run()
{
try
{
isAuthenticated = UserService.ValidateToken();
}
catch (FTNIServiceException e)
{
//eat it
}
finally
{
if (!isAuthenticated)
{
startActivity(new Intent(ProtectedListActivity.this, SignInActivity.class));
finish();
}
}
}
};
validationThread.start();
}
}
然後，我再擴展一步，將我的默認操作欄設置包裝到基類中。
public class ListWithActionBarActivity extends ProtectedListActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public void onContentChanged()
{
ActionBar actionBar = (ActionBar)findViewById(R.id.actionbar);
if (actionBar != null)
{
actionBar.setOnTitleClickListener(new OnClickListener() {
public void onClick(View v) {
startActivity(new Intent(ListWithActionBarActivity.this, SelectSiteActivity.class));
finish();
}
});
SiteModel site = PreferencesHelper.getSite();
actionBar.setTitle(site.Name + " (" + site.Abbreviation + ")");
actionBar.addAction(new IntentAction(ListWithActionBarActivity.this,
new Intent(ListWithActionBarActivity.this, MainMenuActivity.class),
R.drawable.ic_title_home_default));
}
}
public static Intent createIntent(Context context) {
Intent i = new Intent(context, MainMenuActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
return i;
}
protected Intent createShareIntent() {
final Intent intent = new Intent(Intent.ACTION_SEND);
intent.setType("text/plain");
intent.putExtra(Intent.EXTRA_TEXT, "Shared from the ActionBar widget.");
return Intent.createChooser(intent, "Share");
}
}
然後，因爲我具有由狀態分隔的用戶2所列出（懸浮或活性）我試圖將包裝一個除了基類操作欄。
public class UserBase extends ListWithActionBarActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
//setContentView(R.layout.queue);
super.onCreate(savedInstanceState);
ActionBar actionBar = (ActionBar)findViewById(R.id.actionbar);
actionBar.addAction(new UserStatusSelectorAction(UserBase.this));
}
}
最後，我們有我的活動。我已經省略了一些代碼，但是我保留了大部分代碼，以便在顯示加載屏幕時查看通過另一個線程檢索數據的方式，然後構建listview。
public class SuspendedUsersActivity extends ListWithActionBarActivity implements Runnable{
ProgressDialog progress;
ArrayList<UserModel> users;
int position;
@Override
public void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.queue);
super.onCreate(savedInstanceState);
TextView title = (TextView)findViewById(R.id.list_title);
title.setText("Suspended Users");
progress = ProgressDialog.show(SuspendedUsersActivity.this, "", "Loading...", true);
Thread thread = new Thread(SuspendedUsersActivity.this);
thread.start();
}
private void buildListView()
{
ListView lv = getListView();
//registerForContextMenu(lv);
lv.setTextFilterEnabled(true);
lv.clearChoices();
setListAdapter(new UserListAdapter(SuspendedUsersActivity.this, R.layout.useritem, users));
lv.setOnItemClickListener(clickListener);
}
private OnItemClickListener clickListener = new OnItemClickListener()
{
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
UserModel user = users.get(position);
SuspendedUserAction action = new SuspendedUserAction(SuspendedUsersActivity.this, user.UserId);
action.performAction(view);
}
};
@Override
public void run() {
// TODO Auto-generated method stub
SiteModel site = PreferencesHelper.getSite();
try
{
users = UserService.GetSuspendedUsers(site.SiteId);
}
catch (FTNIServiceException e)
{
// TODO Auto-generated catch block
Message message = new Message();
message.what = ActivityBase.RESULT_ERROR;
message.obj = e.getMessage();
handler.sendMessage(message);
return;
}
handler.sendEmptyMessage(ActivityBase.RESULT_DONE);
}
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch(msg.what)
{
case ActivityBase.RESULT_SUCCESS:
progress.dismiss();
startActivity(new Intent(SuspendedUsersActivity.this, SelectSiteActivity.class));
finish();
break;
case ActivityBase.RESULT_DONE:
buildListView();
ApplicationController app = (ApplicationController)getApplication();
app.setSuspendedUsersChanged(false);
progress.dismiss();
break;
case ActivityBase.RESULT_ERROR:
progress.dismiss();
new AlertDialog.Builder(SuspendedUsersActivity.this)
.setMessage(msg.obj.toString())
.setNeutralButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface arg0, int arg1) {
//do nothing
arg0.dismiss();
}
})
.show();
break;
}
}
};
}
它與ProtectedListActivity當我沒有設定一個內容視圖，但一切失敗的，不管是不是我設置的內容視圖和註釋掉動作條的東西。
'getListView（）'是從ListActivity繼承的內置方法。 http://developer.android.com/reference/android/app/ListActivity.html#getListView（） – Josh 2011-03-01 19:14:33
也許您的適配器返回空值。 – 2011-03-01 19:29:34