android - 如何将一个活动中的自定义数组列表传递给另一个活动

Question

我有一个 todolist 应用程序，我无法将一个活动中的自定义列表传递给另一个活动。我使用数据包装器，但是当我单击添加按钮时，程序给出了 nullpointerexception。

这是 AddItem.java

  okButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View arg0) {

            ArrayList<Entry> itemList = new ArrayList<Entry>();

            task = editText1.getText().toString();
            priorityLevel = spinner.getSelectedItem().toString();
            status = toggleButton.getText().toString();

            int day = datePicker.getDayOfMonth();
            int month = datePicker.getMonth() + 1;
            int year = datePicker.getYear();

            date = day + "/" + month + "/" + year;





            itemList.add(new Entry(task, priorityLevel, date, status));

            Intent okIntent = new Intent();
            okIntent.putExtra("item",new DataWrapper(itemList));
            setResult(Activity.RESULT_OK, okIntent);
            finish();
        }
    });

和 MainActivity.java

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == Activity.RESULT_OK) {

        switch (requestCode) {
        case ADD_NOTE:
            Log.w("1", "one");

            DataWrapper dw = (DataWrapper) getIntent().getSerializableExtra("item");

            Log.w("2", "two");

            entryList = dw.getEntryList();

            Log.w("3", "three");

            //String extraName = AddItem.code;
            //ArrayList<Entry> list = data.getParcelableArrayListExtra(extraName);
            todoItems.addAll(entryList);

            Log.w("4", "four");

            todoArrayAdapter.notifyDataSetChanged();

            Log.w("5", "five");

            break;

Answer 1

ArrayList 实现可序列化

您可以使用意图

ArrayList<String> mylist = new ArrayList<String>();  
Intent intent = new Intent(ActivityName.this, Second.class);
intent.putStringArrayListExtra("key", mylist);
startActivity(intent);

检索

Intent i = getIntent();  
ArrayList<String> list = i.getStringArrayListExtra("key");

Answer 2

实现 Parcelable 接口。http://bimbim.in/post/2010/09/27/Android-Passing-object-from-one-activity-to-another.aspx

Answer 3

代替

DataWrapper dw = (DataWrapper) getIntent().getSerializableExtra("item");

和

DataWrapper dw = (DataWrapper) data.getSerializableExtra("item");

在 onActivityResult()...