Java Android:listview中的复选框(如何在适配器中创建OnCheckedChangeListener)
我正在创建一个待办事项列表应用程序,我有一个关于在列表适配器中使用复选框及其侦听器的问题。listview中的单行包含三个文本视图和一个复选框。我想在用户选中复选框时更改单行的背景。我已经读到,我应该在我的适配器类中放入复选框侦听器,所以我就这样做了。现在问题来了——当我在listview中添加几行并对所有行都不选中复选框时,所有行都可以正常工作,但当我添加一行时,选中复选框并尝试添加另一行时,我会出错 java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“void android.view.view.setBackgroundColor(int)” 下面是我的适配器的代码。谢谢你的建议。我只是从Android编程开始,所以感谢您提前理解Java Android:listview中的复选框(如何在适配器中创建OnCheckedChangeListener),java,android,listview,checkbox,adapter,Java,Android,Listview,Checkbox,Adapter,我正在创建一个待办事项列表应用程序,我有一个关于在列表适配器中使用复选框及其侦听器的问题。listview中的单行包含三个文本视图和一个复选框。我想在用户选中复选框时更改单行的背景。我已经读到,我应该在我的适配器类中放入复选框侦听器,所以我就这样做了。现在问题来了——当我在listview中添加几行并对所有行都不选中复选框时,所有行都可以正常工作,但当我添加一行时,选中复选框并尝试添加另一行时,我会出错 java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法
public class ToDoAdapter extends ArrayAdapter<ToDoTask> {
ArrayList<ToDoTask> objects;
Context context;
int resource;
public ToDoAdapter(@NonNull Context context, @LayoutRes int resource, @NonNull ArrayList<ToDoTask> objects) {
super(context, resource, objects);
this.objects = objects;
this.context = context;
this.resource = resource;
}
@Override
public View getView(final int position, View convertView, final ViewGroup parent) {
View view = convertView;
ToDoHolder toDoHolder = null;
if (view == null) {
LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = layoutInflater.inflate(R.layout.row, parent, false);
toDoHolder = new ToDoHolder();
toDoHolder.rowTitle = (TextView) view.findViewById(R.id.rowTitle);
toDoHolder.rowDesc = (TextView) view.findViewById(R.id.rowDesc);
toDoHolder.rowDate = (TextView) view.findViewById(R.id.rowDate);
toDoHolder.rowIsDone = (CheckBox) view.findViewById(R.id.rowCheckBoxDone);
toDoHolder.rowIsDone.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
if(checked){
parent.getChildAt(position).setBackgroundColor(Color.parseColor("#8FE370"));
}
else
parent.getChildAt(position).setBackgroundColor(Color.WHITE);
}
});
view.setTag(toDoHolder);
} else {
toDoHolder = (ToDoHolder) view.getTag();
}
ToDoTask object = objects.get(position);
toDoHolder.rowTitle.setText(object.getTitle());
toDoHolder.rowDesc.setText(object.getDescription());
toDoHolder.rowDate.setText(object.getDate());
toDoHolder.rowIsDone.setChecked(object.getDone());
return view;
}
static class ToDoHolder {
TextView rowTitle;
TextView rowDesc;
TextView rowDate;
CheckBox rowIsDone;
}
}
公共类ToLoadAdapter扩展了ArrayAdapter{
阵列列表对象;
语境;
智力资源;
公共ToDoAdapter(@NonNull上下文上下文、@LayoutRes int-resource、@NonNull数组列表对象){
超级(上下文、资源、对象);
this.objects=对象;
this.context=上下文;
这个资源=资源;
}
@凌驾
公共视图getView(最终整型位置、视图转换视图、最终视图组父视图){
视图=转换视图;
ToDoHolder ToDoHolder=null;
如果(视图==null){
LayoutInflater LayoutInflater=(LayoutInflater)context.getSystemService(context.LAYOUT\u INFLATER\u SERVICE);
视图=布局更平坦。充气(R.layout.row,父级,false);
toDoHolder=新toDoHolder();
toDoHolder.rowTitle=(TextView)view.findViewById(R.id.rowTitle);
toDoHolder.rowDesc=(TextView)view.findViewById(R.id.rowDesc);
toDoHolder.rowDate=(TextView)view.findViewById(R.id.rowDate);
toDoHolder.rowsdone=(复选框)view.findViewById(R.id.rowCheckBoxDone);
toDoHolder.rowsdone.setOnCheckedChangeListener(新建CompoundButton.OnCheckedChangeListener()){
@凌驾
已更改复选框时的公共无效(CompoundButton CompoundButton,布尔值已选中){
如果(选中){
parent.getChildAt(position.setBackgroundColor(Color.parseColor(“#8FE370”));
}
其他的
父.getChildAt(位置).setBackgroundColor(颜色.白色);
}
});
view.setTag(toDoHolder);
}否则{
toDoHolder=(toDoHolder)view.getTag();
}
ToDoTask object=objects.get(位置);
toDoHolder.rowTitle.setText(object.getTitle());
toDoHolder.rowDesc.setText(object.getDescription());
toDoHolder.rowDate.setText(object.getDate());
toDoHolder.rowsdone.setChecked(object.getDone());
返回视图;
}
静态类ToDoHolder{
文本视图行标题;
文本视图行描述;
text查看行日期;
罗伊斯敦;
}
}
下面是我的MainActivity类,它从“AddToToTask”类获取单行元素的详细信息
public类MainActivity扩展了AppCompatActivity{
私有最终int请求代码=1;
ArrayList lista=新的ArrayList();
ToDoAdapter适配器=空;
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
按钮按钮=(按钮)findViewById(R.id.ButtonAd);
ListView ListView=(ListView)findViewById(R.id.ListView);
adapter=newtodoadapter(this,R.layout.row,lista);
setAdapter(适配器);
setOnClickListener(新视图.OnClickListener(){
@凌驾
公共void onClick(视图){
Intent Intent=new Intent(getApplicationContext(),addToToTask.class);
startActivityForResult(意图、请求代码);
}
});
}
@凌驾
受保护的void onActivityResult(int请求代码、int结果代码、意图数据){
super.onActivityResult(请求代码、结果代码、数据);
字符串标题、说明、日期;
布尔isDone;
if(requestCode==1){
if(null!=数据){
title=data.getStringExtra(“title”);
description=data.getStringExtra(“description”);
日期=data.getStringExtra(“日期”);
isDone=data.getBooleanExtra(“完成”,false);
添加(新ToDoTask(标题、说明、日期、isDone));
adapter.notifyDataSetChanged();
}
}
}
}
公共类到加载适配器扩展了ArrayAdapter{
私有ArrayList对象;
私人语境;
私有int资源;
私有SparseBooleanArray checkedPositions=新SparseBooleanArray();
公共ToDoAdapter(@NonNull上下文上下文、@LayoutRes int-resource、@NonNull数组列表对象){
超级(上下文、资源、对象);
this.objects=对象;
this.context=上下文;
这个资源=资源;
}
@凌驾
公共视图getView(int位置、视图转换视图、视图组父视图){
托多霍尔德托多霍尔德;
if(convertView==null){
LayoutInflater LayoutInflater=LayoutInflater.from(上下文);
convertView=LayoutFlater.充气(R.layout.row,父级,false);
toDoHolder=新toDoHolder();
toDoHolder.rowTitle=(TextView)convertView.findViewById(R.id.rowTitle);
toDoHolder.rowDesc=(TextView)convertView.findViewById(R.id.rowDesc);
toDoHolder.rowDate=(TextView)convertView.findViewById(R.id.rowDate);
toDoHolder.rowsdone=(复选框)convertView.findViewById(R.id.rowCheckBoxDone);
setTag(toDoHolder);
}否则{
toDoHolder=(toDoHolder)convertView.getTag();
}
toDoHolder.rowTitle.setTag(位置);
toDoHolder.rowsdone.setTag(convertView);
toDoHolder.rowsdone.setOnCheckedChangeListener(新建CompoundButton.OnCheckedChangeListener())
public class MainActivity extends AppCompatActivity {
private final int requestCode = 1;
ArrayList<ToDoTask> lista = new ArrayList<>();
ToDoAdapter adapter = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = (Button) findViewById(R.id.buttonAdd);
ListView listView = (ListView) findViewById(R.id.listView);
adapter = new ToDoAdapter(this, R.layout.row, lista);
listView.setAdapter(adapter);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), AddToDoTask.class);
startActivityForResult(intent, requestCode);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
String title, description, date;
Boolean isDone;
if (requestCode == 1) {
if (null != data) {
title = data.getStringExtra("title");
description = data.getStringExtra("description");
date = data.getStringExtra("date");
isDone = data.getBooleanExtra("done", false);
lista.add(new ToDoTask(title, description, date, isDone));
adapter.notifyDataSetChanged();
}
}
}
public class ToDoAdapter extends ArrayAdapter<ToDoTask> {
private ArrayList<ToDoTask> objects;
private Context context;
private int resource;
private SparseBooleanArray checkedPositions = new SparseBooleanArray();
public ToDoAdapter(@NonNull Context context, @LayoutRes int resource, @NonNull ArrayList<ToDoTask> objects) {
super(context, resource, objects);
this.objects = objects;
this.context = context;
this.resource = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ToDoHolder toDoHolder;
if (convertView == null) {
LayoutInflater layoutInflater = LayoutInflater.from(context);
convertView = layoutInflater.inflate(R.layout.row, parent, false);
toDoHolder = new ToDoHolder();
toDoHolder.rowTitle = (TextView) convertView.findViewById(R.id.rowTitle);
toDoHolder.rowDesc = (TextView) convertView.findViewById(R.id.rowDesc);
toDoHolder.rowDate = (TextView) convertView.findViewById(R.id.rowDate);
toDoHolder.rowIsDone = (CheckBox) convertView.findViewById(R.id.rowCheckBoxDone);
convertView.setTag(toDoHolder);
} else {
toDoHolder = (ToDoHolder) convertView.getTag();
}
toDoHolder.rowTitle.setTag(position);
toDoHolder.rowIsDone.setTag(convertView);
toDoHolder.rowIsDone.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
View view = (View) compoundButton.getTag();
TextView title = (TextView) view.findViewById(R.id.rowTitle);
int pos = (int) title.getTag();
if (checked) {
checkedPositions.put(pos, true);
view.setBackgroundColor(Color.parseColor("#8FE370"));
} else {
checkedPositions.put(pos, false);
view.setBackgroundColor(Color.WHITE);
}
}
});
ToDoTask object = objects.get(position);
toDoHolder.rowTitle.setText(object.getTitle());
toDoHolder.rowDesc.setText(object.getDescription());
toDoHolder.rowDate.setText(object.getDate());
toDoHolder.rowIsDone.setChecked(object.getDone() || checkedPositions.get(position));
return convertView;
}
private class ToDoHolder {
private TextView rowTitle;
private TextView rowDesc;
private TextView rowDate;
private CheckBox rowIsDone;
}
}
layout.findViewByID(int ID);