[英]Android: Checkbox in listview (how to create OnCheckedChangeListener in Adapter)
我正在创建一个待办事项列表应用程序,我对在列表适配器中使用复选框及其侦听器有疑问。 我在列表视图中的一行包含三个TextView和一个Checkbox。 当用户“选中”复选框时,我想更改单行的背景。 我已经读过我应该将复选框侦听器放在我的适配器类中,所以我做到了。 现在的问题是-当我在列表视图中添加几行并且未选中复选框时,所有这些都可以正常工作,但是当我添加一行时,请选中该复选框并尝试添加另一行时出现错误
java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“ void android.view.View.setBackgroundColor(int)”
以下是我的适配器的代码。 感谢您的任何建议。 我只是从Android编程开始,因此感谢您提前了解。
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;
}
}
下面是我的MainActivity类,该类从“ AddToDoTask”类获取单行元素的详细信息。
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;
}
}
您必须row
xml文件中添加布局,并将布局放入toDoHolder中,然后仅更改布局的背景色。 您可以访问子视图,例如
layout.findViewByID(int ID);
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