Java 从ListView获取子对象会导致在空对象引用上出现android.view.view.view.findViewById(int)
单击my activity_main.xml上的edit按钮时,它会在my main activity中激发此方法Java 从ListView获取子对象会导致在空对象引用上出现android.view.view.view.findViewById(int),java,android,android-layout,listview,Java,Android,Android Layout,Listview,单击my activity_main.xml上的edit按钮时,它会在my main activity中激发此方法 public void editActivity(View view) { editIds.clear(); //Check to see if any activities are ticked (checked) and grab the id if they are. for (int i = 0; i < adapter.getCount();
public void editActivity(View view) {
editIds.clear();
//Check to see if any activities are ticked (checked) and grab the id if they are.
for (int i = 0; i < adapter.getCount(); i++) {
CheckBox c = listView.getChildAt(i).findViewById(R.id.checkBox);
if (c.isChecked()) {
editIds.add(adapter.getItemId(i));
}
}
//If only one item is checked start the Edit activity
if (editIds.size() == 1) {
Intent intent = new Intent(this, EditActivity.class);
intent.putExtra("ID", String.valueOf(editIds.get(0)));
startActivityForResult(intent, 2);
}
//If more than 1 or none are checked inform the user
else {
String output = "VIEW / EDIT: Please select one activity.";
Toast.makeText(this, output, Toast.LENGTH_SHORT).show();
}
}
在列表的大小超过屏幕大小之前,所有这些都可以正常工作。一些研究表明,尽管我的自定义适配器包含整个列表视图的所有条目,但列表视图仅存储可见条目。我想这就是我出错的原因
如何使用选中项id填充ArrayList EditID,以便从SQLite db检索该记录或将其删除
我的适配器:
package com.example.activitytracker;
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.TextView;
public class ActivityAdapter extends CursorAdapter {
public ActivityAdapter(Context context, Cursor cursor) {
super(context, cursor, 0);
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
return LayoutInflater.from(context).inflate(R.layout.activity, parent, false);
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
// Find fields to populate in inflated template
TextView activityTitle = (TextView) view.findViewById(R.id.activityTitle);
TextView activityDescription = (TextView) view.findViewById(R.id.activityDescription);
TextView activityDate = (TextView) view.findViewById(R.id.activityDate);
// Extract properties from cursor
String activity = cursor.getString(cursor.getColumnIndexOrThrow("activity"));
String description = cursor.getString(cursor.getColumnIndexOrThrow("description"));
String date = cursor.getString(cursor.getColumnIndexOrThrow("date"));
// Shorten description for cleaner screen display
String displayValueOfDescription = description;
if (description.length() > 20) {
displayValueOfDescription = description.substring(0, 19) + "...";
}
// Create UK date format for screen display
String yearDB = date.substring(0, 4);
String monthDB = date.substring(5, 7);
String dayDB = date.substring(8, 10);
String dateDB = dayDB + "-" + monthDB + "-" + yearDB;
// Populate fields with extracted properties
activityTitle.setText(activity);
activityDescription.setText(String.valueOf(displayValueOfDescription));
activityDate.setText(String.valueOf(dateDB));
}
public void update(Cursor cursor) {
this.swapCursor(cursor);
this.notifyDataSetChanged();
}
}
My layout_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:theme="@style/AppTheme">
<include
android:id="@+id/toolbar"
layout="@layout/toolbar" />
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="@string/activity"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="18sp"
android:textStyle="italic"
android:padding="5dp"
android:layout_weight="4"/>
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="@string/description"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="18sp"
android:textStyle="italic"
android:padding="5dp"
android:layout_weight="6"/>
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="@string/date"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="18sp"
android:textStyle="italic"
android:padding="5dp"
android:layout_weight="3"/>
</LinearLayout>
<LinearLayout
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.1">
<ListView
android:id="@+id/listView"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme">
<Button
android:id="@+id/edit"
android:onClick="editActivity"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/edit" />
<Button
android:id="@+id/delete"
android:onClick="deleteActivity"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/delete" />
</LinearLayout>
</LinearLayout>
编辑
我已将此代码添加到适配器中
checked.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
// Do the stuff you want for the case when the row TextView is clicked
// you may want to set as the tag for the TextView the position paremeter of the `getView` method and then retrieve it here
Integer realPosition = (Integer) v.getTag();
// using realPosition , now you know the row where this TextView was clicked
Log.d("CLICKEDCHECK", "POS=" + v.getId());
}
});
我正在记录getId,但无论我选中什么复选框,这都是一样的。如何获取该复选框的记录id?然后我可以从数组列表中添加或删除它们。
编辑
使用来自devgianlu的代码进行更新
无论选中哪个框进行编辑或删除,代码都会返回相同的id
这是更新的ActivityAdapter
package com.example.activitytracker;
import android.content.Context;
import android.database.Cursor;
import android.util.SparseBooleanArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CursorAdapter;
import android.widget.TextView;
public class ActivityAdapter extends CursorAdapter {
private final SparseBooleanArray checked = new SparseBooleanArray();
public ActivityAdapter(Context context, Cursor cursor) {
super(context, cursor, 0);
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
return LayoutInflater.from(context).inflate(R.layout.activity, parent, false);
}
@Override
public void bindView(View view, Context context, final Cursor cursor) {
// Find fields to populate in inflated template
TextView activityTitle = (TextView) view.findViewById(R.id.activityTitle);
TextView activityDescription = (TextView) view.findViewById(R.id.activityDescription);
TextView activityDate = (TextView) view.findViewById(R.id.activityDate);
CheckBox check = (CheckBox) view.findViewById(R.id.checkBox);
check.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
checked.put(cursor.getPosition(), isChecked);
}
});
// Extract properties from cursor
String activity = cursor.getString(cursor.getColumnIndexOrThrow("activity"));
String description = cursor.getString(cursor.getColumnIndexOrThrow("description"));
String date = cursor.getString(cursor.getColumnIndexOrThrow("date"));
// Shorten description for cleaner screen display
String displayValueOfDescription = description;
if (description.length() > 20) {
displayValueOfDescription = description.substring(0, 19) + "...";
}
// Create UK date format for screen display
String yearDB = date.substring(0, 4);
String monthDB = date.substring(5, 7);
String dayDB = date.substring(8, 10);
String dateDB = dayDB + "-" + monthDB + "-" + yearDB;
// Populate fields with extracted properties
activityTitle.setText(activity);
activityDescription.setText(String.valueOf(displayValueOfDescription));
activityDate.setText(String.valueOf(dateDB));
}
public boolean isChecked(int pos) {
return checked.get(pos, false);
}
public void update(Cursor cursor) {
this.swapCursor(cursor);
this.notifyDataSetChanged();
}
}
以及我对MainActivity中isChecked方法的调用
public void editActivity(View view) {
editIds.clear();
//Check to see if any activities are ticked (checked) and grab the id if they are.
// Add checked items to deleteIds
for (int i = 0; i < adapter.getCount(); i++) {
if (adapter.isChecked(i)) {
editIds.add(adapter.getItemId(i));
Log.d("EDITACT", "ID="+adapter.getItemId(i) + "size="+editIds.size());
}
}
//If only one item is checked start the Edit activity
if (editIds.size() == 1) {
Intent intent = new Intent(this, EditActivity.class);
intent.putExtra("ID", String.valueOf(editIds.get(0)));
startActivityForResult(intent, 2);
}
//If more than 1 or none are checked inform the user
else {
String output = "VIEW / EDIT: Please select one activity.";
Toast.makeText(this, output, Toast.LENGTH_SHORT).show();
}
}
进一步更新
我的ActivityAdapter现在看起来像这样
package com.example.activitytracker;
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import java.util.ArrayList;
import java.util.List;
class Activities {
private boolean checked = false;
private DBManager dbManager;
Cursor cursor = dbManager.fetch();
public Activities(Cursor cursor) {
List<Activities> items = new ArrayList<>();
while (cursor.moveToNext()){
items.add(new Activities(cursor));
}
}
}
public class ActivityAdapter extends BaseAdapter {
private final List<Activities> items;
private final LayoutInflater inflater;
public ActivityAdapter(Context context, List<Activities> items) {
this.items = items;
this.inflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(R.layout.activity, parent, false);
}
final Activities item = items.get(position);
CheckBox checkBox = convertView.findViewById(R.id.checkBox);
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// item.isChecked() = isChecked;
}
});
// *** Bind the data to the view ***
return convertView;
}
public boolean isChecked(int pos) {
// return items.get(pos).checked;
return true;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
}
此外,现在我的适配器在启动时没有填充我的listView,对适配器的任何调用都会使应用程序崩溃
这里是我用来检查listview中复选框的地方,然后刷新适配器。我不知道现在该怎么办
deleteIds.clear();
// Add checked items to deleteIds
for (int i = 0; i < adapter.getCount(); i++) {
CheckBox c = listView.getChildAt(i).findViewById(R.id.checkBox);
if (c.isChecked()) {
deleteIds.add(adapter.getItemId(i));
}
}
//Check to see if any activities are ticked (checked)
if (deleteIds.size() > 0) {
//If there are checked activities a dialog is displayed for user to confirm
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure you want to delete?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
for (int i = 0; i < deleteIds.size(); i++) {
dbManager.delete(deleteIds.get(i));
adapter.update(dbManager.fetch());
}
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
deleteIds.clear();
dialog.cancel();
}
}).show();
}
}
非常感谢您迄今为止的帮助。这是我编写的一段代码,用于将所有光标数据放入对象中,然后将这些对象绑定到视图。这样,控制复选框状态就容易多了
public class CustomItem {
public boolean checked = false;
public CustomItem(Cursor cursor) {
// Get yuor data and put it in the object
}
}
public class CustomAdapter extends BaseAdapter {
private final List<CustomItem> items;
private final LayoutInflater inflater;
public CustomAdapter(Context context, List<CustomItem> items) {
this.items = items;
this.inflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(/* Your layout ID */, parent, false);
}
final CustomItem item = items.get(position);
CheckBox checkBox = convertView.findViewById(R.id.checkBox);
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
item.checked = isChecked;
}
});
// *** Bind the data to the view ***
return convertView;
}
public boolean isChecked(int pos) {
return items.get(pos).checked;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
}
Cursor cursor = ....;
List<CustomItem> items = new ArrayList<>();
while (cursor.moveToNext())
items.add(new CustomItem(cursor));
Adapter adapter = new BaseAdapter(this /* Your activity */, items);
listView.setAdapter(adapter);
for (int i = 0; i < adapter.getCount(); i++) {
System.out.println(i + " IS " + adapter.isChecked(i));
}
您正在尝试在适配器创建视图之前获取该视图。您应该保存适配器本身的复选框状态。@devgianlu在列表超出屏幕之前,它都会工作。我不知道如何在适配器中保存复选框状态。如果可以的话,一个小的示例代码将非常好。谢谢。My ide不喜欢此行public void onCheckedChangedCompoundButton buttonView、boolean isChecked{checked.putcursor.getPosition、isChecked;}checked和游标抛出错误通过更改复选框变量名称修复,因为它与SparseBooleanArray共享。光标所在的行中仍有错误。IDE说我应该将变量设为final。?我必须在bindView中将光标设为final,并更改复选框的变量。无论勾选哪个框,始终返回相同的ID。我想我的更改可能是问题的原因。当我遍历所有适配器项时,只有最后一项被标记为选中。我的项不是按数据库ID顺序显示的,而是按时间顺序降序显示的,这有什么区别吗?
package com.example.activitytracker;
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import java.util.ArrayList;
import java.util.List;
class Activities {
private boolean checked = false;
private DBManager dbManager;
Cursor cursor = dbManager.fetch();
public Activities(Cursor cursor) {
List<Activities> items = new ArrayList<>();
while (cursor.moveToNext()){
items.add(new Activities(cursor));
}
}
}
public class ActivityAdapter extends BaseAdapter {
private final List<Activities> items;
private final LayoutInflater inflater;
public ActivityAdapter(Context context, List<Activities> items) {
this.items = items;
this.inflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(R.layout.activity, parent, false);
}
final Activities item = items.get(position);
CheckBox checkBox = convertView.findViewById(R.id.checkBox);
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// item.isChecked() = isChecked;
}
});
// *** Bind the data to the view ***
return convertView;
}
public boolean isChecked(int pos) {
// return items.get(pos).checked;
return true;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
}
deleteIds.clear();
// Add checked items to deleteIds
for (int i = 0; i < adapter.getCount(); i++) {
CheckBox c = listView.getChildAt(i).findViewById(R.id.checkBox);
if (c.isChecked()) {
deleteIds.add(adapter.getItemId(i));
}
}
//Check to see if any activities are ticked (checked)
if (deleteIds.size() > 0) {
//If there are checked activities a dialog is displayed for user to confirm
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure you want to delete?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
for (int i = 0; i < deleteIds.size(); i++) {
dbManager.delete(deleteIds.get(i));
adapter.update(dbManager.fetch());
}
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
deleteIds.clear();
dialog.cancel();
}
}).show();
}
}
public class CustomItem {
public boolean checked = false;
public CustomItem(Cursor cursor) {
// Get yuor data and put it in the object
}
}
public class CustomAdapter extends BaseAdapter {
private final List<CustomItem> items;
private final LayoutInflater inflater;
public CustomAdapter(Context context, List<CustomItem> items) {
this.items = items;
this.inflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(/* Your layout ID */, parent, false);
}
final CustomItem item = items.get(position);
CheckBox checkBox = convertView.findViewById(R.id.checkBox);
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
item.checked = isChecked;
}
});
// *** Bind the data to the view ***
return convertView;
}
public boolean isChecked(int pos) {
return items.get(pos).checked;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int position) {
return items.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
}
Cursor cursor = ....;
List<CustomItem> items = new ArrayList<>();
while (cursor.moveToNext())
items.add(new CustomItem(cursor));
Adapter adapter = new BaseAdapter(this /* Your activity */, items);
listView.setAdapter(adapter);
for (int i = 0; i < adapter.getCount(); i++) {
System.out.println(i + " IS " + adapter.isChecked(i));
}