Ich versuche, eine Einkaufslisten-App basierend auf Eingabefeldern ArrayList
und zusammenzustellen ListView
. Die App basiert auf Fragments
. Ich bin jedoch auf ein Problem gestoßen und weiß nicht, wie ich es lösen soll.
Ich habe mich sowohl bei Google als auch bei StackOverflow umgesehen und einige Informationen gefunden. Ich habe es jedoch nicht zum Laufen gebracht. Jetzt hoffe ich, dass ich Hilfe mit meinem Code bekommen kann.
Ich bin relativ unerfahren in der Android-Entwicklung.
Main.java
import java.util.ArrayList;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
import android.view.MenuItem;
public class Main extends FragmentActivity {
ArrayList<Detail> items = new ArrayList<Detail>();
FragmentManager FM;
FragmentTransaction FT;
Input input = new Input();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
replaceFragment(R.id.container, input);
}
public void replaceFragment(int container, Fragment fragment){
FM = getFragmentManager();
FT = FM.beginTransaction();
FT.replace(container, fragment);
FT.commit();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
ListAdapter.java
public class ListAdapter extends BaseAdapter {
Context context;
ArrayList<Detail> items;
public ListAdapter(Context context, ArrayList<Detail> items) {
this.context = context;
this.items = items;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return items.indexOf(getItem(position));
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null){
LayoutInflater lInflater = (LayoutInflater)context.getSystemService(
Activity.LAYOUT_INFLATER_SERVICE);
convertView = lInflater.inflate(R.layout.list_row, null);
}
TextView title = (TextView)convertView.findViewById(R.id.itemTitle);
CheckBox done = (CheckBox)convertView.findViewById(R.id.itemDone);
Detail detail_position = items.get(position);
title.setText(detail_position.getTitle());
done.setChecked(detail_position.isDone());
return null;
}
}
List.java
import java.util.ArrayList;
import android.app.ListFragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
public class List extends ListFragment implements OnItemClickListener{
ArrayList<Detail> items;
ListAdapter adapter;
private onClickListener OCL;
interface onClickListener{
public void onItemClick(int id);
}
public List(ArrayList<Detail> items) {
this.items = items;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.list_layout, container, false);
return root;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if(items != null){
adapter = new ListAdapter(getActivity(), items);
setListAdapter(adapter);
getListView().setOnItemClickListener(this);
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
if(OCL != null){
OCL.onItemClick(position);
}
}
}
list_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:id="@+id/android:list"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</ListView>
</LinearLayout>
list_row
<?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="horizontal"
android:padding="10dp" >
<TextView
android:id="@+id/itemTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="0.96"
android:text="Medium Text"
android:textAppearance="?android:attr/textAppearanceMedium" />
<CheckBox
android:id="@+id/itemDone"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Done" />
</LinearLayout>
activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
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="com.example.com.hermods.lab2_2.Main" >
</RelativeLayout>
Log
02-19 09:10:47.421: E/AndroidRuntime(12745): Process: com.example.com.hermods.lab2_2, PID: 12745
02-19 09:10:47.421: E/AndroidRuntime(12745): java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.AbsListView.obtainView(AbsListView.java:2360)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.ListView.makeAndAddView(ListView.java:1864)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.ListView.fillDown(ListView.java:698)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.ListView.fillFromTop(ListView.java:759)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.ListView.layoutChildren(ListView.java:1673)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.AbsListView.onLayout(AbsListView.java:2148)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.Choreographer.doCallbacks(Choreographer.java:580)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.Choreographer.doFrame(Choreographer.java:550)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.os.Handler.handleCallback(Handler.java:739)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.os.Handler.dispatchMessage(Handler.java:95)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.os.Looper.loop(Looper.java:135)
02-19 09:10:47.421: E/AndroidRuntime(12745): at android.app.ActivityThread.main(ActivityThread.java:5221)
02-19 09:10:47.421: E/AndroidRuntime(12745): at java.lang.reflect.Method.invoke(Native Method)
02-19 09:10:47.421: E/AndroidRuntime(12745): at java.lang.reflect.Method.invoke(Method.java:372)
02-19 09:10:47.421: E/AndroidRuntime(12745): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
02-19 09:10:47.421: E/AndroidRuntime(12745): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
android
android-layout
android-fragments
android-listview
user2734182
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return items.indexOf(getItem(position));
gleich a istposition
in Ihrem Fall? Das erste, was Sie ausprobieren müssen, ist, den Konstruktor aus zu entfernenList
.Antworten:
public View getView
Wechseln Siereturn null;
in Ihrer Methode zureturn convertView;
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convertView
das jemals so seinnull
sollte? Hat es eine besondere Bedeutung?View
. Wenn Sie zurückkehrennull
, erhalten Sie genau dieselbe Fehlermeldung.#verwenden
return convertView;
Code:
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in Ihrer baseadapter Klasse Konstruktor versuchen zu initialisieren LayoutInflater , normalerweise bevorzugt i auf diese Weise,
Ich hoffe, dies wird Ihnen helfen, wenn Sie oben in der Klasse die Variable LayoutInflater erstellen
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Es tritt manchmal auf, wenn wir in einer Fragmentaktivität einen benutzerdefinierten Adapter verwenden. und wir geben ein Nullobjekt zurück, dh eine Nullansicht, damit die Aktivität verwirrt wird, welche Ansicht geladen werden soll, weshalb diese Ausnahme auftritt
Zeigt die Position an, an der die Ansicht geändert werden soll
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