java.lang.NullPointerException：尝试调用空对象引用的虚拟方法'int android.view.View.getImportantForAccessibility（）'
我试图根据input字段， ArrayList和ListView放在一起的购物清单应用程序。 该应用程序将基于Fragments 。 但是，我遇到了一个问题，我不知道如何解决它。
我在Google和StackOverflow上都find了一些信息。 但是，我没有得到它的工作。 现在希望我可以得到我的代码的帮助。
我在Android开发方面相对缺乏经验。
提前致谢
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中
<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>
日志
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)
在你的public View getView方法的改变return null; return convertView; 。
#use return convertView;
码：
public View getView(final int position, View convertView, ViewGroup parent) { convertView = null; if (convertView == null) { LayoutInflater mInflater = (LayoutInflater) context .getSystemService(Activity.LAYOUT_INFLATER_SERVICE); convertView = mInflater.inflate(R.layout.list_item, null); TextView tv = (TextView) convertView.findViewById(R.id.name); Button rm_btn = (Button) convertView.findViewById(R.id.rm_btn); Model m = modelList.get(position); tv.setText(m.getName()); // click listiner for remove button คลิกลบปุ่ม rm_btn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { modelList.remove(position); notifyDataSetChanged(); } }); } ///#use return convertView; return convertView; }
在你的baseadapter类构造函数尝试初始化LayoutInflater ，通常我喜欢这种方式，
public ClassBaseAdapter(Context context,ArrayList<Integer> listLoanAmount) { this.context = context; this.listLoanAmount = listLoanAmount; this.layoutInflater = LayoutInflater.from(context); }
在类的顶部创buildLayoutInflatervariables，希望这会对你有所帮助
