我的问题是我的listView没有显示任何项目。我在SQLite数据库中输入了多列数据，我想在自定义列表视图中显示它，但是listView什么都没有显示。我认为问题出在我的自定义适配器中，尤其是在getView（）方法中。我用Log消息跟踪数据流，并将存储在数据库中的数据存储到ArrayList中，但似乎getView（）不会将值放入TextView中。我尝试了许多教程，但它总是使我成为“自定义数据类”并更改我的漏洞代码。请帮我。我已经在这个问题上待了几个星期了。
我的自定义适配器ListAdapter
import android.app.Activity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.ArrayList;
public class ListAdapter extends ArrayAdapter<String> {
private final Activity context;
private final ArrayList<String> items;
public ListAdapter(Activity context, ArrayList<String> items) {
super(context, R.layout.custom_list, items);
// TODO Auto-generated constructor stub
this.context=context;
this.items=items;
}
@Override
public int getCount() {
return items.size();
}
public View getView(int position, View view, ViewGroup parent) {
LayoutInflater inflater=context.getLayoutInflater();
View rowView=inflater.inflate(R.layout.custom_list, null,true);
TextView nameTV = rowView.findViewById(R.id.nameTV);
TextView priceTV = rowView.findViewById(R.id.priceTV);
//nameTV.setText(names[position]);
//priceTV.setText(prices[position].toString());
nameTV.setText(items.get(2*position));
priceTV.setText(items.get(2*position+1));
Log.d("ListAdapter", "nameTV.setText: items.get(2*position) "+nameTV+"/////////////////////////////");
Log.d("ListAdapter", "priceTV.setText: items.get(2*position) "+priceTV+"/////////////////////////////");
Log.d("ListAdapter", "getView : -----------------------------");
return rowView;
}
}
我的主要活动ListDataActivity
import android.content.Intent;
import android.database.Cursor;
import android.support.v4.view.MenuItemCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.support.v7.widget.SearchView;
import android.widget.Toast;
import java.util.ArrayList;
public class ListDataActivity extends AppCompatActivity {
DatabaseHelper databaseHelper;
ListView listView;
ArrayList<String> listData;
ListAdapter listAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_data);
databaseHelper = new DatabaseHelper(this);
listView = findViewById(R.id.listView);
listData = new ArrayList<String>();
listAdapter = new com.example.barcodescanner.ListAdapter(this,listData);
listView.setAdapter(listAdapter);
popListView();
}
private void popListView() {
Log.d("ListDataActivity","Displaying data in the ListView");
//get data and append to a list
Cursor data = databaseHelper.getData();
listData = new ArrayList<>();
while (data.moveToNext()) {
//get the data from the columns
//then add it to the ArrayList
listData.add(data.getString(1));
listData.add(data.getString(2));
Log.d("DatabaseHelper", "addData: Adding "+data.getString(1)+"+++++++++++++++++++++++++++++");
Log.d("DatabaseHelper", "addData: Adding "+data.getString(2)+"+++++++++++++++++++++++++++++");
//create the list adapter and set the adapter
//final ListAdapter adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listData);
listView.setAdapter(listAdapter);
//set an OnClickListener to the listView
//we can use Object for data type here
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
String name = adapterView.getItemAtPosition(i).toString();
String price = adapterView.getItemAtPosition(i).toString(); // we can use Object for data type here
Log.d("ListDataActivity", "onItemClick: You Clicked on " + name);
Cursor data = databaseHelper.getItemID(name); //get the id associated with that name
int itemID = -1;
while (data.moveToNext()){
itemID = data.getInt(0);
}
if (itemID > -1){
Log.d("ListDataActivity","onItemClick: the ID is : "+itemID);
Intent editScreenIntent = new Intent(ListDataActivity.this,EditDataActivity.class);
editScreenIntent.putExtra("id",itemID);
editScreenIntent.putExtra("name",name);
editScreenIntent.putExtra("price",price);
startActivity(editScreenIntent);
//finish();
}else {
toastMessage("No ID associate with this name");
}
}
});
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.search_menu,menu);
MenuItem searchItem = menu.findItem(R.id.item_search);
SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
ArrayList<String> userslist = new ArrayList<>();
for(String user : listData){
if(user.toLowerCase().contains(newText.toLowerCase())){
userslist.add(user);
}
}
//ArrayAdapter<String> adapter = new ArrayAdapter<>(ListDataActivity.this,
// android.R.layout.simple_list_item_1,userslist);
listView.setAdapter(listAdapter);
return true;
}
});
return super.onCreateOptionsMenu(menu);
}
//customized toast message
private void toastMessage(String message){
Toast.makeText(this,message,Toast.LENGTH_SHORT).show();
}
}
我的自定义列表布局custom_list
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<LinearLayout android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:id="@+id/nameTV"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Name"
android:textStyle="bold"
android:textAppearance="?android:attr/textAppearanceMedium"
android:layout_marginLeft="20dp"
android:layout_marginRight="100dp"
android:layout_marginTop="5dp"
android:textColor="#4d4d4d"
/>
<TextView
android:id="@+id/priceTV"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Price"
android:textStyle="bold"
android:textAppearance="?android:attr/textAppearanceMedium"
android:layout_marginLeft="20dp"
android:layout_marginRight="10dp"
android:layout_marginTop="5dp"
android:textColor="#4d4d4d"
/>
</LinearLayout>
</LinearLayout>
</android.support.constraint.ConstraintLayout>
活动列表数据
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ListDataActivity">
<ListView
android:id="@+id/listView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</ListView>
</android.support.constraint.ConstraintLayout>
在onCreate方法中，您将空的ArrayList传递到适配器中。然后，您调用popListView，然后将listData变量重新初始化为一个新对象（new ArrayList()）。因此，您的适配器永远不会收到任何数据。
在创建适配器之前，将呼叫移至popListView最多2行。
更新
创建一个新的类，如下所示：
class DataStructure {
private String name;
private String price;
DataStructure(String name, String price) {
this.name = name;
this.price = price;
}
String getName() {
return name;
}
String getPrice() {
return price;
}
}
然后用class ListAdapter extends ArrayAdapter<DataStructure>更改适配器类型
当您从数据库中读取时，创建一个新的DataStructure实例并将每个实例添加到列表中。