错误:尝试调用虚拟方法';void android.widget.ListView.setAdapter(android.widget.ListAdapter)和#x27;关于空对象引用
我已经创建了一个使用适配器来绑定我的项目。但是,我不知道为什么在运行应用程序时会显示此错误(尝试在空对象引用上调用虚拟方法'void android.widget.ListView.setAdapter(android.widget.ListAdapter')) 我的适配器错误:尝试调用虚拟方法';void android.widget.ListView.setAdapter(android.widget.ListAdapter)和#x27;关于空对象引用,android,Android,我已经创建了一个使用适配器来绑定我的项目。但是,我不知道为什么在运行应用程序时会显示此错误(尝试在空对象引用上调用虚拟方法'void android.widget.ListView.setAdapter(android.widget.ListAdapter')) 我的适配器 package com.example.redir.wealthtrack; import android.app.Activity; import android.content.Context; import andr
package com.example.redir.wealthtrack;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import com.example.redir.wealthtrack.model.Receipt;
import com.example.redir.wealthtrack.model.Usage;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.ArrayList;
/**
* Created by User on 2/3/2016.
*/
public class UsageAdapter extends ArrayAdapter<Usage> {
private static final String TAG = "Usage" ;
ArrayList<Usage> list;
Context context;
public static final String LOGTAG = "EXPLORECE";
public UsageAdapter(Context context, int resource, ArrayList<Usage> lists){
super(context, resource, lists);
this.context = context;
this.list = lists;
}
public View getView(int position, View convertView, ViewGroup parent) {
Usage myusage = list.get(position);
LayoutInflater inflater =
(LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(R.layout.usage_item, null);
return view;
}
}
package com.example.redir.wealthtrack;
导入android.app.Activity;
导入android.content.Context;
导入android.graphics.Bitmap;
导入android.graphics.BitmapFactory;
导入android.net.Uri;
导入android.view.LayoutInflater;
导入android.view.view;
导入android.view.ViewGroup;
导入android.widget.ArrayAdapter;
导入android.widget.ImageView;
导入com.example.redir.wealthtrack.model.Receipt;
导入com.example.redir.wealthtrack.model.Usage;
导入java.io.FileNotFoundException;
导入java.io.InputStream;
导入java.util.ArrayList;
/**
*用户于2016年2月3日创建。
*/
公共类UsageAdapter扩展了ArrayAdapter{
私有静态最终字符串TAG=“用法”;
数组列表;
语境;
公共静态最终字符串LOGTAG=“EXPLORECE”;
public UseAdapter(上下文、int资源、ArrayList列表){
超级(上下文、资源、列表);
this.context=上下文;
this.list=列表;
}
公共视图getView(int位置、视图转换视图、视图组父视图){
用法myusage=list.get(位置);
充气机=
(LayoutInflater)context.getSystemService(Activity.LAYOUT\u flater\u SERVICE);
视图=充气机。充气(R.layout.usage\u项,空);
返回视图;
}
}
我的碎片
package com.example.redir.wealthtrack;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.text.Html;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.GridView;
import android.widget.ListView;
import android.widget.Toast;
import com.example.redir.wealthtrack.db.ReceiptsDataSource;
import com.example.redir.wealthtrack.db.UsageDataSource;
import com.example.redir.wealthtrack.model.Receipt;
import com.example.redir.wealthtrack.model.Usage;
import java.util.ArrayList;
import java.util.List;
/**
* A simple {@link Fragment} subclass.
*/
public class UsageFragment extends Fragment {
public UsageDataSource Usagedatasource;
ArrayAdapter<Usage> UsageAdapter;
ListView listView;
List<Usage> usages;
Usage selectedUsage;
public UsageFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
showToast(getActivity().getApplicationContext(), "Usage's history");
((MainActivity) getActivity()).setActionBarTitle("View Usage");
Usagedatasource = new UsageDataSource(getActivity().getApplicationContext());
Usagedatasource.open();
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_receipts, container, false);
usages = (List<Usage>) Usagedatasource.getAll();
UsageAdapter = new UsageAdapter(getActivity().getApplicationContext(),0, (ArrayList<Usage>) usages);
listView = (ListView) view.findViewById(R.id.listView3);
listView.setAdapter(UsageAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectedUsage = usages.get(position);
AlertDialog.Builder a_builder = new AlertDialog.Builder(getActivity());
a_builder.setMessage("Receipt/Bill captured on: " + selectedUsage.getUsagedate())
.setCancelable(false)
.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
AlertDialog alert = a_builder.create();
alert.setTitle(Html.fromHtml("<font color='#08ae9e'>Information</font>"));
alert.show();
}
});
listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
selectedUsage = usages.get(position);
AlertDialog.Builder a_builder = new AlertDialog.Builder(getActivity());
a_builder.setMessage("Are you sure you want to delete?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
deleteItem(selectedUsage);
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = a_builder.create();
alert.setTitle(Html.fromHtml("<font color='#08ae9e'>Alert!!</font>"));
alert.show();
return true;
}
});
return view;
}
public static void showToast(Context context, String text) {
Toast.makeText(context, text, Toast.LENGTH_LONG).show();
}
private void deleteItem(Usage selectedUsage) {
Usagedatasource.removeUsage(selectedUsage);
showToast(getActivity().getApplicationContext(), "Usage deleted");
UsageAdapter.notifyDataSetChanged();
UsageAdapter.notifyDataSetInvalidated();
refreshDisplay();
}
private void refreshDisplay() {
usages = Usagedatasource.getAll();
UsageAdapter.clear();
UsageAdapter.addAll(usages);
}
}
package com.example.redir.wealthtrack;
导入android.app.AlertDialog;
导入android.content.Context;
导入android.content.DialogInterface;
导入android.os.Bundle;
导入android.support.v4.app.Fragment;
导入android.text.Html;
导入android.view.LayoutInflater;
导入android.view.view;
导入android.view.ViewGroup;
导入android.widget.AdapterView;
导入android.widget.ArrayAdapter;
导入android.widget.GridView;
导入android.widget.ListView;
导入android.widget.Toast;
导入com.example.redir.wealthrack.db.ReceiptsDataSource;
导入com.example.redir.wealthtrack.db.UsageDataSource;
导入com.example.redir.wealthtrack.model.Receipt;
导入com.example.redir.wealthtrack.model.Usage;
导入java.util.ArrayList;
导入java.util.List;
/**
*一个简单的{@link Fragment}子类。
*/
公共类UsageFragment扩展了片段{
公共用途数据源UsageDataSource;
ArrayAdapter UsageAdapter;
列表视图列表视图;
列出用途;
使用选择教育;
公共用途片段(){
//必需的空公共构造函数
}
@凌驾
创建视图上的公共视图(布局、充气机、视图组容器、,
Bundle savedInstanceState){
super.onCreate(savedInstanceState);
showToast(getActivity().getApplicationContext(),“使用历史”);
((MainActivity)getActivity()).setActionBarTitle(“查看用法”);
Usagedatasource=新的Usagedatasource(getActivity().getApplicationContext());
Usagedatasource.open();
//为该碎片膨胀布局
视图=充气机。充气(R.layout.fragment_收据,容器,假);
usages=(List)Usagedatasource.getAll();
UsageAdapter=新UsageAdapter(getActivity().getApplicationContext(),0,(ArrayList)usages);
listView=(listView)view.findViewById(R.id.listView3);
setAdapter(UsageAdapter);
setOnItemClickListener(新的AdapterView.OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView父对象、视图、整型位置、长id){
selectedUsage=usages.get(位置);
AlertDialog.Builder a_Builder=新建AlertDialog.Builder(getActivity());
a_builder.setMessage(“在:+selectedUsage.getUsagedate()上捕获的收据/票据”)
.setCancelable(错误)
.setPositiveButton(“确定”,新的DialogInterface.OnClickListener(){
@凌驾
public void onClick(DialogInterface dialog,int which){
}
});
AlertDialog alert=a_builder.create();
alert.setTitle(Html.fromHtml(“信息”));
alert.show();
}
});
setOnItemLongClickListener(新的AdapterView.OnItemLongClickListener(){
@凌驾
公共布尔值长单击(AdapterView父项、视图、整型位置、长id){
selectedUsage=usages.get(位置);
AlertDialog.Builder a_Builder=新建AlertDialog.Builder(getActivity());
a_builder.setMessage(“确实要删除吗?”)
.setCancelable(错误)
.setPositiveButton(“是”,新的DialogInterface.OnClickListener(){
@凌驾
public void onClick(DialogInterface dialog,int which){
删除项(selectedUsage);
}
})
.setNegativeButton(“否”,新的DialogInterface.OnClickListener(){
@凌驾
public void onClick(DialogInterface dialog,int which){
dialog.cancel();
}
});
AlertDialog alert=a_builder.create();
alert.setTitle(Html.fromHtml(“alert!!”));
alert.show();
返回true;
}
});
返回视图;
}
公共静态void showtoos(上下文上下文)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Medium Text"
android:id="@+id/textView2"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="70dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Medium Text"
android:id="@+id/textView3"
android:layout_below="@+id/textView2"
android:layout_centerHorizontal="true"
android:layout_marginTop="57dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Medium Text"
android:id="@+id/textView4"
android:layout_centerVertical="true"
android:layout_alignStart="@+id/textView3" />
</RelativeLayout>
<LinearLayout 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"
tools:context=".ReceiptFragment"
android:weightSum="1">
<!-- TODO: Update blank fragment layout -->
<GridView
android:layout_width="wrap_content"
android:layout_height="503dp"
android:id="@+id/gridView"
android:numColumns="auto_fit"
android:horizontalSpacing="5dp"
android:columnWidth="120dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:layout_marginTop="70dp"
android:padding="8dp"
/>
</LinearLayout>
public List<Usage> getAll() {
List<Usage> usages = new ArrayList<Usage>();
Cursor cursor = database.query(WealthDBOpenHelper.TABLE_USAGE, allColumns,
null, null, null, null, null);
if (cursor.getCount() > 0) {
while (cursor.moveToNext()) {
Usage usage = new Usage();
usage.setUsagedate(cursor.getString(cursor.getColumnIndex(WealthDBOpenHelper.COLUMN_USAGE_DATE)));
usage.setAmount(cursor.getDouble(cursor.getColumnIndex(WealthDBOpenHelper.COLUMN_AMOUNT)));
usage.setCategory(cursor.getString(cursor.getColumnIndex(WealthDBOpenHelper.COLUMN_CATEGORY)));
usages.add(usage);
}
}
return usages;
}
GridView gridView;
gridView = (GridView) view.findViewById(R.id.gridView);
gridView.setAdapter(UsageAdapter);
tools:context=".UsageFragment"