java - 将图像从对话框拖放到 Activity 时出现问题

Question

我不断收到NullPointerException。我无法将图像从我的对话框 fragment 获取到我的主要 Activity 。对话框中的项目拖到主 Activity 中。但是，当我删除图像时，应用程序崩溃了，因为它没有获取我拖动的图像。那么如何将图像从我的对话框拖放到我的主要 Activity 中？请帮我解决这个问题。

Main Activity

public class MainActivity extends AppCompatActivity implements View.OnDragListener, View.OnLongClickListener {

    private static final String TAG = MainActivity.class.getSimpleName();
    private ImageView imageView;
    private static final String IMAGE_VIEW_TAG = "ONION";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViews();
        implementEvents();

    }

    private void findViews() {
        imageView = findViewById(R.id.image_view);
        imageView.setTag(IMAGE_VIEW_TAG);
    }


    //Implement long click and drag listener
    private void implementEvents() {
        imageView.setOnLongClickListener(this);

        findViewById(R.id.Imgbutton10).setOnDragListener(this);
        findViewById(R.id.Imgbutton11).setOnDragListener(this);
        findViewById(R.id.Imgbutton12).setOnDragListener(this);
        findViewById(R.id.Imgbutton13).setOnDragListener(this);
        findViewById(R.id.Imgbutton14).setOnDragListener(this);
    }

    @Override
    public boolean onLongClick(View view) {
        ClipData.Item item = new ClipData.Item((CharSequence) view.getTag());
        String[] mimeTypes = {ClipDescription.MIMETYPE_TEXT_PLAIN};

        ClipData data = new ClipData(view.getTag().toString(), mimeTypes, item);
        View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);

        view.startDrag(data,shadowBuilder,view,0);
        view.setVisibility(View.INVISIBLE);
        return true;
    }

    @Override
    public boolean onDrag(View view, DragEvent event) {
            int action = event.getAction();

            switch (action) {
                case DragEvent.ACTION_DRAG_STARTED:

                    if (event.getClipDescription().hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) {
                        return true;
                    }

                    return false;

                case DragEvent.ACTION_DRAG_ENTERED:
                    view.getBackground().setColorFilter(Color.DKGRAY, PorterDuff.Mode.SRC_IN);
                    view.invalidate();
                    return true;

                case DragEvent.ACTION_DRAG_LOCATION:
                    // Ignore the event
                    return true;

                case DragEvent.ACTION_DRAG_EXITED:
                    view.getBackground().clearColorFilter();
                    view.invalidate();
                    return true;

                case DragEvent.ACTION_DROP:
                    ClipData.Item item = event.getClipData().getItemAt(0);
                    String dragData = item.getText().toString();
                    Toast.makeText(this, "Dragged data is " + dragData, Toast.LENGTH_SHORT).show();
                    view.getBackground().clearColorFilter();
                    view.invalidate();

                    View v = (View) event.getLocalState();
                    ViewGroup owner = (ViewGroup) v.getParent();
                    owner.removeView(v);
                    LinearLayout container = (LinearLayout) view;
                    container.addView(v);
                    v.setVisibility(View.VISIBLE);

                    return true;

                case DragEvent.ACTION_DRAG_ENDED:
                    view.getBackground().clearColorFilter();
                    view.invalidate();
                    if (event.getResult())
                        Toast.makeText(this, "The drop was handled.", Toast.LENGTH_SHORT).show();

                    else
                        Toast.makeText(this, "The drop didn't work.", Toast.LENGTH_SHORT).show();

                    return true;

                default:
                    Log.e("DragDrop Example", "Unknown action type received by OnDragListener.");
                    break;
            }
            return false;
        }
}

Dialog Fragment

public class VegyFrag extends DialogFragment implements View.OnLongClickListener,View.OnDragListener {

    private static final String Tag = "VegyFrag";
    private ImageView imageView;
    private static final String IMAGE_VIEW_TAG = "ONION";

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View myView = inflater.inflate(R.layout.dialog_add, container, false);
        imageView = myView.findViewById(R.id.ic2);
        imageView.setTag(IMAGE_VIEW_TAG);
        implementEvents();
        return myView;
    }


    private void implementEvents() {
        //add or remove any view that you don't want to be dragged
        imageView.setOnLongClickListener(this);
   ((MainActivity)getActivity()).findViewById(R.id.Imgbutton10).setOnDragListener(this);
        ((MainActivity)getActivity()).findViewById(R.id.Imgbutton11).setOnDragListener(this);
        ((MainActivity)getActivity()).findViewById(R.id.Imgbutton12).setOnDragListener(this);
        ((MainActivity)getActivity()).findViewById(R.id.Imgbutton13).setOnDragListener(this);
        ((MainActivity)getActivity()).findViewById(R.id.Imgbutton14).setOnDragListener(this);

    }

    @Override
    public boolean onLongClick(View view) {
        ClipData.Item item = new ClipData.Item((CharSequence) view.getTag());
        String[] mimeTypes = {ClipDescription.MIMETYPE_TEXT_PLAIN};

        ClipData data = new ClipData(view.getTag().toString(), mimeTypes, item);
        View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);

        view.startDrag(data,shadowBuilder,view,0);
        view.setVisibility(View.INVISIBLE);
        getDialog().dismiss();
        return true;
    }

    @Override
    public boolean onDrag(View view, DragEvent event) {
        int action = event.getAction();

        switch (action) {
            case DragEvent.ACTION_DRAG_STARTED:

                if (event.getClipDescription().hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) {
                    return true;

                }
                return false;

            case DragEvent.ACTION_DRAG_ENTERED:
                view.getBackground().setColorFilter(Color.DKGRAY, PorterDuff.Mode.SRC_IN);
                view.invalidate();
                return true;

            case DragEvent.ACTION_DRAG_LOCATION:
                return true;

            case DragEvent.ACTION_DRAG_EXITED:
                view.getBackground().clearColorFilter();
                view.invalidate();
                return true;

            case DragEvent.ACTION_DROP:
                ClipData.Item item = event.getClipData().getItemAt(0);
                String dragData = item.getText().toString();
                view.getBackground().clearColorFilter();
                view.invalidate();

                View v = (View) event.getLocalState();
                ViewGroup owner = (ViewGroup) v.getParent();
                owner.removeView(v);
                LinearLayout container = (LinearLayout) view;
                container.addView(v);
                v.setVisibility(View.VISIBLE);

                return true;

            case DragEvent.ACTION_DRAG_ENDED:
                view.getBackground().clearColorFilter();
                view.invalidate();
                return true;

            default:
                Log.e("DragDrop Example", "Unknown action type received by OnDragListener.");
                break;
        }
        return false;
    }

}

提前谢谢

Answer 1

我也找不到使用 DialogFragment 执行此操作的方法，因此我找到了解决方法。 DialogFragments 的问题是，当对话框关闭时， View 会被破坏，因此您会遇到 NPE。为了解决这个问题，我向底层 fragment 的 View 添加了一个看起来像对话框的 View (使用 CardView)。当需要显示“对话框”时，我只需将可见性设置为 View.VISIBLE，当需要隐藏它时，我将其设置为 View.GONE。这使得您拖动的 View 能够保留与 fragment 相同的上下文的一部分，并且当隐藏“对话框”时它不会被破坏。