我想实现一个待办事项列表应用程序。我有三个活动：一个主要活动，一个添加活动和一个编辑活动。在我的主要活动中，有一个添加按钮和一个显示待办事项的列表视图。当我单击添加按钮时，将执行添加活动。在这个活动中，有一个任务的编辑文本、一个日期选择器和一个优先级微调器。单击确定按钮时，所有这些输入的值都将作为一行发送到主活动的列表视图。并且，当单击此列表中的项目时，将执行编辑活动并且用户可以更改值。另一个细节是，每次待办事项都根据它们的优先级排序，我会根据截止日期给它们不同的颜色。但是，我不知道如何为此安排自定义适配器。我的自定义适配器类给出了一个空指针异常。谁能帮我重新安排我的自定义适配器类？先感谢您。
主要活动：
public class MainActivity extends Activity {
protected static final String main = "mainTask";
private ToDoItemAdapter listAdapter;
ArrayList<String> listString;
ArrayList<ToDoItem> listItems;
private int pos;
public static final int ADD_TASKS = 1;
public static final int EDIT_TASKS = 2;
Button button;
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(savedInstanceState == null || !savedInstanceState.containsKey("key"))
{
listString = new ArrayList<String>();
listItems = new ArrayList<ToDoItem>();
}
else
{
listString = savedInstanceState.getStringArrayList("datas");
listItems = savedInstanceState.getParcelableArrayList("key");
}
initUI();
setListener();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private void initUI() {
getViewReferences();
initializeToDoList();
}
private void setListener() {
// TODO Auto-generated method stub
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent addTaskIntent = new Intent(MainActivity.this, AddActivity.class);
startActivityForResult(addTaskIntent, ADD_TASKS);
}
});
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
pos = arg2;
String sentTask = listItems.get(pos).getTask();
String sentDate = listItems.get(pos).getDeadline();
String sentPriority = listItems.get(pos).getPriority();
String sentStatus = listItems.get(pos).getStatus();
ArrayList<String> sentDatas = new ArrayList<String>();
sentDatas.add(sentTask);
sentDatas.add(sentDate);
sentDatas.add(sentPriority);
sentDatas.add(sentStatus);
Intent editTaskIntent = new Intent(MainActivity.this, EditingTask.class);
editTaskIntent.putExtra("mainTask", sentDatas);
startActivityForResult(editTaskIntent, EDIT_TASKS);
}
});
}
private void getViewReferences() {
// TODO Auto-generated method stub
button = (Button) findViewById(R.id.addButton);
listView = (ListView) findViewById(R.id.listView);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
private void initializeToDoList() {
// TODO Auto-generated method stub
//listItems = new ArrayList<ToDoItem>();
//listString = new ArrayList<String>();
listAdapter = new ToDoItemAdapter(this, R.layout.activity_main, listItems);
listView.setAdapter(listAdapter);
View noTaskView = findViewById(R.id.emptyToDoList);
listView.setEmptyView(noTaskView);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
if (resultCode == Activity.RESULT_OK) {
switch (requestCode) {
case ADD_TASKS:
try {
updateToDoList(data);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
case EDIT_TASKS:
try {
editToDoList(data);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
default:
break;
}
}
super.onActivityResult(requestCode, resultCode, data);
}
private void editToDoList(Intent data) throws ParseException {
// TODO Auto-generated method stub
String toDoEdited = EditingTask.edits;
ArrayList<String> listEdited = data.getStringArrayListExtra(toDoEdited);
if(listEdited.size() != 0)
{
String editedTask = listEdited.get(0);
String editedDeadline = listEdited.get(1);
String editedPriority = listEdited.get(2);
String editedStatus = listEdited.get(3);
listItems.get(pos).setTask(editedTask);
listItems.get(pos).setDeadline(editedDeadline);
listItems.get(pos).setPriority(editedPriority);
listItems.get(pos).setStatus(editedStatus);
}
else
{
listItems.remove(pos);
}
setTheAdapter();
}
private void setTheAdapter() throws ParseException {
// TODO Auto-generated method stub
sortListItems(listItems);
refreshListString(listString, listItems);
listAdapter.notifyDataSetChanged();
}
private void updateToDoList(Intent data) throws ParseException {
// TODO Auto-generated method stub
String task = AddActivity.tasks;
ArrayList<String> list = data.getStringArrayListExtra(task);
String addedTask = list.get(0);
String addedDeadline = list.get(1);
String addedPriority = list.get(2);
ToDoItem item = new ToDoItem(addedTask, addedDeadline ,"NOT DONE", addedPriority);
listItems.add(item);
setTheAdapter();
}
private void refreshListString(ArrayList<String> listString2,
ArrayList<ToDoItem> listItems2) {
listString2.clear();
int size = listItems2.size();
for(int i = 0; i < size; i++)
{
listString2.add(listItems2.get(i).toString());
}
}
private void sortListItems(ArrayList<ToDoItem> listItems2) {
int length = listItems2.size();
ToDoItem myItem;
for(int i = 0; i < length; i++)
{
for(int j = 1; j < (length-i); j++)
if(listItems2.get(j-1).getPriority().compareTo(listItems2.get(j).getPriority()) < 0)
{
myItem = listItems2.get(j-1);
listItems2.set(j-1, listItems2.get(j));
listItems2.set(j, myItem);
}
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putStringArrayList("datas", listString);
outState.putParcelableArrayList("key", listItems);
}
}
我的自定义适配器类：
public class ToDoItemAdapter extends ArrayAdapter<ToDoItem> {
Context context;
private int resource;
ArrayList<ToDoItem> todoItem;
public ToDoItemAdapter(Context context, int resource, ArrayList<ToDoItem> objects) {
super(context, resource, objects);
this.context = context;
this.resource = resource;
this.todoItem = objects;
}
@Override
public ToDoItem getItem(int position) {
return this.todoItem.get(position);
}
@Override
public int getCount() {
return this.todoItem.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
View row;
if (convertView == null)
{
/*todoView = new LinearLayout(getContext());
String inflater = Context.LAYOUT_INFLATER_SERVICE;
LayoutInflater li;
li = (LayoutInflater)getContext().getSystemService(inflater);
li.inflate(resource, todoView, true);
*/
LayoutInflater inflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = inflater.inflate(resource, parent, false);
}
else
{
row = convertView;
ListView list = (ListView) row.findViewById(R.id.listView);
int len = todoItem.size();
for(int i = 0; i < len; i++)
{
String deadline = todoItem.get(i).getDeadline();
String status = todoItem.get(i).getStatus();
String currentDate = findCurrentDate();
SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
Date data=null;
try {
data = sdf.parse(deadline);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Date current =null;
try {
current = sdf.parse(currentDate);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(status.equals("DONE"))
{
list.getChildAt(i).setBackgroundColor(0xff00ff00);
}
else
{
if(data.compareTo(current)>0 || data.compareTo(current)==0){
list.getChildAt(i).setBackgroundColor(0x01060018);
}else if(data.compareTo(current)<0){
list.getChildAt(i).setBackgroundColor(0x01060016);
}
}
}
}
return row;
}
private String findCurrentDate() {
// TODO Auto-generated method stub
Calendar cal = Calendar.getInstance();
int year = cal.get(Calendar.YEAR);
int month = cal.get(Calendar.MONTH);
int day = cal.get(Calendar.DAY_OF_MONTH);
String date = day+"-"+(month+1)+"-"+year;
return date;
}
}
主要的xml：
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity"
android:orientation="vertical">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/add_buton"
android:id="@+id/addButton"/>
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/listView"
></ListView>
<TextView android:id="@+id/emptyToDoList"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1.0"
android:gravity="center"
android:text="@string/no_task"
android:textColor="@color/warning" />
日志猫：
11-14 04:11:36.795: E/AndroidRuntime(1472): FATAL EXCEPTION: main
11-14 04:11:36.795: E/AndroidRuntime(1472): java.lang.NullPointerException
11-14 04:11:36.795: E/AndroidRuntime(1472): at com.example.enhancedtodolistapplication.ToDoItemAdapter.getView(ToDoItemAdapter.java:94)
待办事项类别：
public class ToDoItem implements Parcelable{
String task;
String deadline;
String status;
String priority;
public ToDoItem(String task, String deadline, String status, String priority) {
super();
this.task = task;
this.deadline = deadline;
this.status = status;
this.priority = priority;
}
private ToDoItem(Parcel in) {
task = in.readString();
deadline = in.readString();
status = in.readString();
priority = in.readString();
}
public String getTask() {
return task;
}
public void setTask(String task) {
this.task = task;
}
public String getDeadline() {
return deadline;
}
public void setDeadline(String deadline) {
this.deadline = deadline;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public String getPriority() {
return priority;
}
public void setPriority(String priority) {
this.priority = priority;
}
@Override
public String toString() {
return priority + " " + task + " " + deadline + " " + status;
}
@Override
public int describeContents() {
// TODO Auto-generated method stub
return 0;
}
@Override
public void writeToParcel(Parcel out, int flags) {
// TODO Auto-generated method stub
out.writeString(task);
out.writeString(deadline);
out.writeString(status);
out.writeString(priority);
}
public static final Parcelable.Creator<ToDoItem> CREATOR = new Parcelable.Creator<ToDoItem>() {
public ToDoItem createFromParcel(Parcel in) {
return new ToDoItem(in);
}
public ToDoItem[] newArray(int size) {
return new ToDoItem[size];
}
};
}