MultiSelect Spinner or dialog to choose multiple items

MultiselectDialog.java

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

/**
 * Created by arthtilva
 */
public class MultiSelectDialog {
    String[] _items = null;
    boolean[] mSelection = null;
    boolean[] mSelectionAtStart = null;
    String _itemsAtStart = null;
    ArrayAdapter<String> simple_adapter;
    Activity activity;
    Button button;
    String prompt;
    String positiveText = "Done";
    String negativeText = "Cancel";

    public MultiSelectDialog(Activity activity, Button button, String prompt) {
        if (button == null) {
            throw new NullPointerException("Initialize Button before MultiSelectDialog !!!");
        }
        this.activity = activity;
        this.button = button;
        this.prompt = prompt;
        simple_adapter = new ArrayAdapter<String>(activity, R.layout.category_spinner);
    }

    public void setButtonsText(String positiveText, String negativeText) {
        this.positiveText = positiveText;
        this.negativeText = negativeText;
    }

    public void showMultiDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(activity);
        builder.setMultiChoiceItems(_items, mSelection, new DialogInterface.OnMultiChoiceClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int which, boolean isChecked) {
                if (mSelection != null && which < mSelection.length) {
                    mSelection[which] = isChecked;
                    simple_adapter.clear();
                    simple_adapter.add(buildSelectedItemString());
                } else {
                    throw new IllegalArgumentException("Argument 'which' is out of bounds.");
                }
            }
        });


        builder.setPositiveButton(positiveText, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                System.arraycopy(mSelection, 0, mSelectionAtStart, 0, mSelection.length);
                _itemsAtStart = getSelectedItemsAsString();
                if (_itemsAtStart.length() == 0) {
                    button.setText(prompt);
                } else {
                    button.setText(_itemsAtStart);
                }
                //TODO:MapActivity.setCount(getSelectedIndices().size());

            }
        });
        builder.setNegativeButton(negativeText, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                simple_adapter.clear();
                simple_adapter.add(_itemsAtStart);
                System.arraycopy(mSelectionAtStart, 0, mSelection, 0, mSelectionAtStart.length);
            }
        });
        builder.show();
    }

    private String buildSelectedItemString() {
        StringBuilder sb = new StringBuilder();
        boolean foundOne = false;

        for (int i = 0; i < _items.length; ++i) {
            if (mSelection[i]) {
                if (foundOne) {
                    sb.append(", ");
                }
                foundOne = true;

                sb.append(_items[i]);
            }
        }
        return sb.toString();
    }

    public String getSelectedItemsAsString() {
        StringBuilder sb = new StringBuilder();
        boolean foundOne = false;
        for (int i = 0; i < _items.length; ++i) {
            if (mSelection[i]) {
                if (foundOne) {
                    sb.append(", ");
                }
                foundOne = true;
                sb.append(_items[i]);
            }
        }
        return sb.toString();
    }

    public void setItems(String[] items) {
        _items = items;
        mSelection = new boolean[_items.length];
        mSelectionAtStart = new boolean[_items.length];
        simple_adapter.clear();
        simple_adapter.add(_items[0]);
        Arrays.fill(mSelection, false);
        mSelection[0] = true;
        mSelectionAtStart[0] = true;
        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setItems(List<String> items) {
        _items = items.toArray(new String[items.size()]);
        mSelection = new boolean[_items.length];
        mSelectionAtStart = new boolean[_items.length];
        simple_adapter.clear();
        simple_adapter.add(_items[0]);
        Arrays.fill(mSelection, false);
        mSelection[0] = true;
        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setSelection(String[] selection) {
        for (String cell : selection) {
            for (int j = 0; j < _items.length; ++j) {
                if (_items[j].equals(cell)) {
                    mSelection[j] = true;
                    mSelectionAtStart[j] = true;
                }
            }
        }
        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setSelection(List<String> selection) {
        for (int i = 0; i < mSelection.length; i++) {
            mSelection[i] = false;
            mSelectionAtStart[i] = false;
        }
        for (String sel : selection) {
            for (int j = 0; j < _items.length; ++j) {
                if (_items[j].equals(sel)) {
                    mSelection[j] = true;
                    mSelectionAtStart[j] = true;
                }
            }
        }
        simple_adapter.clear();
        simple_adapter.add(buildSelectedItemString());

        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setSelection(int index) {
        for (int i = 0; i < mSelection.length; i++) {
            mSelection[i] = false;
            mSelectionAtStart[i] = false;
        }
        if (index >= 0 && index < mSelection.length) {
            mSelection[index] = true;
            mSelectionAtStart[index] = true;
        } else {
            throw new IllegalArgumentException("Index " + index + " is out of bounds.");
        }
        simple_adapter.clear();
        simple_adapter.add(buildSelectedItemString());
        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setSelection(int[] selectedIndices) {
        for (int i = 0; i < mSelection.length; i++) {
            mSelection[i] = false;
            mSelectionAtStart[i] = false;
        }
        for (int index : selectedIndices) {
            if (index >= 0 && index < mSelection.length) {
                mSelection[index] = true;
                mSelectionAtStart[index] = true;
            } else {
                throw new IllegalArgumentException("Index " + index + " is out of bounds.");
            }
        }
        simple_adapter.clear();
        simple_adapter.add(buildSelectedItemString());

        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public void setClearSelection() {
        for (int i = 0; i < mSelection.length; i++) {
            mSelection[i] = false;
            mSelectionAtStart[i] = false;
        }
        simple_adapter.clear();
        simple_adapter.add(buildSelectedItemString());

        _itemsAtStart = getSelectedItemsAsString();
        if (_itemsAtStart.length() == 0) {
            button.setText(prompt);
        } else {
            button.setText(_itemsAtStart);
        }
    }

    public List<String> getSelectedStrings() {
        List<String> selection = new LinkedList<String>();
        for (int i = 0; i < _items.length; ++i) {
            if (mSelection[i]) {
                selection.add(_items[i]);
            }
        }
        return selection;
    }

    public List<Integer> getSelectedIndices() {
        List<Integer> selection = new LinkedList<Integer>();
        for (int i = 0; i < _items.length; ++i) {
            if (mSelection[i]) {
                selection.add(i);
            }
        }
        return selection;
    }
}

    /*============= XML Code=============*/
    <?xml version="1.0" encoding="utf-8"?>
<Button xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@android:id/text1"
        style="?android:attr/spinnerItemStyle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/transparent"
        android:ellipsize="marquee"
        android:singleLine="true"
        android:textColor="@color/white" />