Přečtení generického typu. – Java – Fórum – Programujte.com

Mám univerzální třídu pro DragNdrop listview. Chci jí udělat univerzální aby se dala použít pro veškeré typy Adapterů, nezáleží na tom, co zobrazují. Jsem trochu začátečník v generických typech. 

Třída, které nese informace pro konkrétní Adapter zobrazující se v ListView.

public class CategoryItem {
	
	public String name;
	public long categoryID;
	
	public CategoryItem(long categoryID, String name) {
		this.name = name;
		this.categoryID = categoryID;
	}

}

nebo například: 

public class OfferItem {

	public long ID;
	public String name;
	public int price;
	public int DPH;
	public long categoryID;

	public OfferItem(long ID, String name, int price, int DPH, long categoryID) {
		this.ID=ID;
		this.name=name;
		this.price=price;
		this.DPH=DPH;
		this.categoryID=categoryID;
	}

}

trochu upravené třída z GoogleDev pro DragNDrop listView, chtěl bych jí udělat univerzální, nezáleží na třídě s daty.

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/…/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.wesikprograming.cisnik.database;

import Interfaces.InterUpdate;
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ObjectAnimator;
import android.animation.TypeEvaluator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ListView;

import java.util.ArrayList;

import com.wesikprograming.cisnik.customedatatypes.CategoryItem;
import com.wesikprograming.cisnik.listViewAdapters.CategoryAdapter;

/**
 * The dynamic listview is an extension of listview that supports cell dragging
 * and swapping.
 *
 * This layout is in charge of positioning the hover cell in the correct location
 * on the screen in response to user touch events. It uses the position of the
 * hover cell to determine when two cells should be swapped. If two cells should
 * be swapped, all the corresponding data set and layout changes are handled here.
 *
 * If no cell is selected, all the touch events are passed down to the listview
 * and behave normally. If one of the items in the listview experiences a
 * long press event, the contents of its current visible state are captured as
 * a bitmap and its visibility is set to INVISIBLE. A hover cell is then created and
 * added to this layout as an overlaying BitmapDrawable above the listview. Once the
 * hover cell is translated some distance to signify an item swap, a data set change
 * accompanied by animation takes place. When the user releases the hover cell,
 * it animates into its corresponding position in the listview.
 *
 * When the hover cell is either above or below the bounds of the listview, this
 * listview also scrolls on its own so as to reveal additional content.
 * @param <T>
 */
public class DynamicListView<T> extends ListView {
	
	private final String tag = "DynamicListView";

    private final int SMOOTH_SCROLL_AMOUNT_AT_EDGE = 15;
    private final int MOVE_DURATION = 150;
    private final int LINE_THICKNESS = 15;

    public ArrayList<T> mCheeseList;

    private int mLastEventY = -1;

    private int mDownY = -1;
    private int mDownX = -1;

    private int mTotalOffset = 0;

    private boolean mCellIsMobile = false;
    private boolean mIsMobileScrolling = false;
    private int mSmoothScrollAmountAtEdge = 0;

    private final int INVALID_ID = -1;
    private long mAboveItemId = INVALID_ID;
    private long mMobileItemId = INVALID_ID;
    private long mBelowItemId = INVALID_ID;

    private BitmapDrawable mHoverCell;
    private Rect mHoverCellCurrentBounds;
    private Rect mHoverCellOriginalBounds;

    private final int INVALID_POINTER_ID = -1;
    private int mActivePointerId = INVALID_POINTER_ID;

    private boolean mIsWaitingForScrollFinish = false;
    private int mScrollState = OnScrollListener.SCROLL_STATE_IDLE;

    public DynamicListView(Context context) {
        super(context);
        init(context);
    }

    public DynamicListView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }

    public DynamicListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public void init(Context context) {
        setOnItemLongClickListener(mOnItemLongClickListener);
        setOnScrollListener(mScrollListener);
        DisplayMetrics metrics = context.getResources().getDisplayMetrics();
        mSmoothScrollAmountAtEdge = (int)(SMOOTH_SCROLL_AMOUNT_AT_EDGE / metrics.density);
    }

    /**
     * Listens for long clicks on any items in the listview. When a cell has
     * been selected, the hover cell is created and set up.
     */
    private AdapterView.OnItemLongClickListener mOnItemLongClickListener =
            new AdapterView.OnItemLongClickListener() {
                public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int pos, long id) {
                    mTotalOffset = 0;

                    int position = pointToPosition(mDownX, mDownY);
                    int itemNum = position - getFirstVisiblePosition();

                    View selectedView = getChildAt(itemNum);
                    mMobileItemId = getAdapter().getItemId(position);
                    mHoverCell = getAndAddHoverView(selectedView);
                    selectedView.setVisibility(INVISIBLE);

                    mCellIsMobile = true;

                    updateNeighborViewsForID(mMobileItemId);

                    return true;
                }
            };

    /**
     * Creates the hover cell with the appropriate bitmap and of appropriate
     * size. The hover cell's BitmapDrawable is drawn on top of the bitmap every
     * single time an invalidate call is made.
     */
    private BitmapDrawable getAndAddHoverView(View v) {

        int w = v.getWidth();
        int h = v.getHeight();
        int top = v.getTop();
        int left = v.getLeft();

        Bitmap b = getBitmapWithBorder(v);

        BitmapDrawable drawable = new BitmapDrawable(getResources(), b);

        mHoverCellOriginalBounds = new Rect(left, top, left + w, top + h);
        mHoverCellCurrentBounds = new Rect(mHoverCellOriginalBounds);

        drawable.setBounds(mHoverCellCurrentBounds);

        return drawable;
    }

    /** Draws a black border over the screenshot of the view passed in. */
    private Bitmap getBitmapWithBorder(View v) {
        Bitmap bitmap = getBitmapFromView(v);
        Canvas can = new Canvas(bitmap);

        Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());

        Paint paint = new Paint();
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(LINE_THICKNESS);
        paint.setColor(Color.BLACK);

        can.drawBitmap(bitmap, 0, 0, null);
        can.drawRect(rect, paint);

        return bitmap;
    }

    /** Returns a bitmap showing a screenshot of the view passed in. */
    private Bitmap getBitmapFromView(View v) {
        Bitmap bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas (bitmap);
        v.draw(canvas);
        return bitmap;
    }

    /**
     * Stores a reference to the views above and below the item currently
     * corresponding to the hover cell. It is important to note that if this
     * item is either at the top or bottom of the list, mAboveItemId or mBelowItemId
     * may be invalid.
     */
    private void updateNeighborViewsForID(long itemID) {
        int position = getPositionForID(itemID);
        CategoryAdapter adapter = ((CategoryAdapter)getAdapter());
        mAboveItemId = adapter.getItemId(position - 1);
        mBelowItemId = adapter.getItemId(position + 1);
    }

    /** Retrieves the view in the list corresponding to itemID */
    public View getViewForID (long itemID) {
        int firstVisiblePosition = getFirstVisiblePosition();
        CategoryAdapter adapter = ((CategoryAdapter)getAdapter());
        for(int i = 0; i < getChildCount(); i++) {
            View v = getChildAt(i);
            int position = firstVisiblePosition + i;
            long id = adapter.getItemId(position);
            if (id == itemID) {
                return v;
            }
        }
        return null;
    }

    /** Retrieves the position in the list corresponding to itemID */
    public int getPositionForID (long itemID) {
        View v = getViewForID(itemID);
        if (v == null) {
            return -1;
        } else {
            return getPositionForView(v);
        }
    }

    /**
     *  dispatchDraw gets invoked when all the child views are about to be drawn.
     *  By overriding this method, the hover cell (BitmapDrawable) can be drawn
     *  over the listview's items whenever the listview is redrawn.
     */
    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        if (mHoverCell != null) {
            mHoverCell.draw(canvas);
        }
    }

    @Override
    public boolean onTouchEvent (MotionEvent event) {

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                mDownX = (int)event.getX();
                mDownY = (int)event.getY();
                mActivePointerId = event.getPointerId(0);
                break;
            case MotionEvent.ACTION_MOVE:
                if (mActivePointerId == INVALID_POINTER_ID) {
                    break;
                }

                int pointerIndex = event.findPointerIndex(mActivePointerId);

                mLastEventY = (int) event.getY(pointerIndex);
                int deltaY = mLastEventY - mDownY;

                if (mCellIsMobile) {
                    mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left,
                            mHoverCellOriginalBounds.top + deltaY + mTotalOffset);
                    mHoverCell.setBounds(mHoverCellCurrentBounds);
                    invalidate();

                    handleCellSwitch();

                    mIsMobileScrolling = false;
                    handleMobileCellScroll();

                    return false;
                }
                break;
            case MotionEvent.ACTION_UP:
                touchEventsEnded();
                break;
            case MotionEvent.ACTION_CANCEL:
                touchEventsCancelled();
                break;
            case MotionEvent.ACTION_POINTER_UP:
                /* If a multitouch event took place and the original touch dictating
                 * the movement of the hover cell has ended, then the dragging event
                 * ends and the hover cell is animated to its corresponding position
                 * in the listview. */
                pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                        MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                final int pointerId = event.getPointerId(pointerIndex);
                if (pointerId == mActivePointerId) {
                    touchEventsEnded();
                }
                break;
            default:
                break;
        }

        return super.onTouchEvent(event);
    }

    /**
     * This method determines whether the hover cell has been shifted far enough
     * to invoke a cell swap. If so, then the respective cell swap candidate is
     * determined and the data set is changed. Upon posting a notification of the
     * data set change, a layout is invoked to place the cells in the right place.
     * Using a ViewTreeObserver and a corresponding OnPreDrawListener, we can
     * offset the cell being swapped to where it previously was and then animate it to
     * its new position.
     */
    private void handleCellSwitch() {
        final int deltaY = mLastEventY - mDownY;
        int deltaYTotal = mHoverCellOriginalBounds.top + mTotalOffset + deltaY;

        View belowView = getViewForID(mBelowItemId);
        View mobileView = getViewForID(mMobileItemId);
        View aboveView = getViewForID(mAboveItemId);

        boolean isBelow = (belowView != null) && (deltaYTotal > belowView.getTop());
        boolean isAbove = (aboveView != null) && (deltaYTotal < aboveView.getTop());

        if (isBelow || isAbove) {

            final long switchItemID = isBelow ? mBelowItemId : mAboveItemId;
            View switchView = isBelow ? belowView : aboveView;
            final int originalItem = getPositionForView(mobileView);

            if (switchView == null) {
                updateNeighborViewsForID(mMobileItemId);
                return;
            }

            swapElements(mCheeseList, originalItem, getPositionForView(switchView));

            ((InterUpdate) getAdapter()).Update(mCheeseList);

            mDownY = mLastEventY;

            final int switchViewStartTop = switchView.getTop();

            mobileView.setVisibility(View.VISIBLE);
            switchView.setVisibility(View.INVISIBLE);

            updateNeighborViewsForID(mMobileItemId);

            final ViewTreeObserver observer = getViewTreeObserver();
            observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
                public boolean onPreDraw() {
                    observer.removeOnPreDrawListener(this);

                    View switchView = getViewForID(switchItemID);

                    mTotalOffset += deltaY;

                    int switchViewNewTop = switchView.getTop();
                    int delta = switchViewStartTop - switchViewNewTop;

                    switchView.setTranslationY(delta);

                    ObjectAnimator animator = ObjectAnimator.ofFloat(switchView,
                            View.TRANSLATION_Y, 0);
                    animator.setDuration(MOVE_DURATION);
                    animator.start();

                    return true;
                }
            });
        }
    }

    private <T> void swapElements(ArrayList<T> arrayList, int indexOne, int indexTwo) {
    	Log.e(tag, "swap");
    	
    	T temp = arrayList.get(indexOne);
        arrayList.set(indexOne, arrayList.get(indexTwo));
        arrayList.set(indexTwo, temp);
    }


    /**
     * Resets all the appropriate fields to a default state while also animating
     * the hover cell back to its correct location.
     */
    private void touchEventsEnded () {
        final View mobileView = getViewForID(mMobileItemId);
        if (mCellIsMobile|| mIsWaitingForScrollFinish) {
            mCellIsMobile = false;
            mIsWaitingForScrollFinish = false;
            mIsMobileScrolling = false;
            mActivePointerId = INVALID_POINTER_ID;

            // If the autoscroller has not completed scrolling, we need to wait for it to
            // finish in order to determine the final location of where the hover cell
            // should be animated to.
            if (mScrollState != OnScrollListener.SCROLL_STATE_IDLE) {
                mIsWaitingForScrollFinish = true;
                return;
            }

            mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left, mobileView.getTop());

            ObjectAnimator hoverViewAnimator = ObjectAnimator.ofObject(mHoverCell, "bounds",
                    sBoundEvaluator, mHoverCellCurrentBounds);
            hoverViewAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator valueAnimator) {
                    invalidate();
                }
            });
            hoverViewAnimator.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationStart(Animator animation) {
                    setEnabled(false);
                }

                @Override
                public void onAnimationEnd(Animator animation) {
                    mAboveItemId = INVALID_ID;
                    mMobileItemId = INVALID_ID;
                    mBelowItemId = INVALID_ID;
                    mobileView.setVisibility(VISIBLE);
                    mHoverCell = null;
                    setEnabled(true);
                    invalidate();
                }
            });
            hoverViewAnimator.start();
        } else {
            touchEventsCancelled();
        }
    }

    /**
     * Resets all the appropriate fields to a default state.
     */
    private void touchEventsCancelled () {
        View mobileView = getViewForID(mMobileItemId);
        if (mCellIsMobile) {
            mAboveItemId = INVALID_ID;
            mMobileItemId = INVALID_ID;
            mBelowItemId = INVALID_ID;
            mobileView.setVisibility(VISIBLE);
            mHoverCell = null;
            invalidate();
        }
        mCellIsMobile = false;
        mIsMobileScrolling = false;
        mActivePointerId = INVALID_POINTER_ID;
    }

    /**
     * This TypeEvaluator is used to animate the BitmapDrawable back to its
     * final location when the user lifts his finger by modifying the
     * BitmapDrawable's bounds.
     */
    private final static TypeEvaluator<Rect> sBoundEvaluator = new TypeEvaluator<Rect>() {
        public Rect evaluate(float fraction, Rect startValue, Rect endValue) {
            return new Rect(interpolate(startValue.left, endValue.left, fraction),
                    interpolate(startValue.top, endValue.top, fraction),
                    interpolate(startValue.right, endValue.right, fraction),
                    interpolate(startValue.bottom, endValue.bottom, fraction));
        }

        public int interpolate(int start, int end, float fraction) {
            return (int)(start + fraction * (end - start));
        }
    };

    /**
     *  Determines whether this listview is in a scrolling state invoked
     *  by the fact that the hover cell is out of the bounds of the listview;
     */
    private void handleMobileCellScroll() {
        mIsMobileScrolling = handleMobileCellScroll(mHoverCellCurrentBounds);
    }

    /**
     * This method is in charge of determining if the hover cell is above
     * or below the bounds of the listview. If so, the listview does an appropriate
     * upward or downward smooth scroll so as to reveal new items.
     */
    public boolean handleMobileCellScroll(Rect r) {
        int offset = computeVerticalScrollOffset();
        int height = getHeight();
        int extent = computeVerticalScrollExtent();
        int range = computeVerticalScrollRange();
        int hoverViewTop = r.top;
        int hoverHeight = r.height();

        if (hoverViewTop <= 0 && offset > 0) {
            smoothScrollBy(-mSmoothScrollAmountAtEdge, 0);
            return true;
        }

        if (hoverViewTop + hoverHeight >= height && (offset + extent) < range) {
            smoothScrollBy(mSmoothScrollAmountAtEdge, 0);
            return true;
        }

        return false;
    }

    public void setCheeseList(ArrayList<T> cheeseList) {
        mCheeseList = cheeseList;
    }

    /**
     * This scroll listener is added to the listview in order to handle cell swapping
     * when the cell is either at the top or bottom edge of the listview. If the hover
     * cell is at either edge of the listview, the listview will begin scrolling. As
     * scrolling takes place, the listview continuously checks if new cells became visible
     * and determines whether they are potential candidates for a cell swap.
     */
    private AbsListView.OnScrollListener mScrollListener = new AbsListView.OnScrollListener () {

        private int mPreviousFirstVisibleItem = -1;
        private int mPreviousVisibleItemCount = -1;
        private int mCurrentFirstVisibleItem;
        private int mCurrentVisibleItemCount;
        private int mCurrentScrollState;

        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                             int totalItemCount) {
            mCurrentFirstVisibleItem = firstVisibleItem;
            mCurrentVisibleItemCount = visibleItemCount;

            mPreviousFirstVisibleItem = (mPreviousFirstVisibleItem == -1) ? mCurrentFirstVisibleItem
                    : mPreviousFirstVisibleItem;
            mPreviousVisibleItemCount = (mPreviousVisibleItemCount == -1) ? mCurrentVisibleItemCount
                    : mPreviousVisibleItemCount;

            checkAndHandleFirstVisibleCellChange();
            checkAndHandleLastVisibleCellChange();

            mPreviousFirstVisibleItem = mCurrentFirstVisibleItem;
            mPreviousVisibleItemCount = mCurrentVisibleItemCount;
        }

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            mCurrentScrollState = scrollState;
            mScrollState = scrollState;
            isScrollCompleted();
        }

        /**
         * This method is in charge of invoking 1 of 2 actions. Firstly, if the listview
         * is in a state of scrolling invoked by the hover cell being outside the bounds
         * of the listview, then this scrolling event is continued. Secondly, if the hover
         * cell has already been released, this invokes the animation for the hover cell
         * to return to its correct position after the listview has entered an idle scroll
         * state.
         */
        private void isScrollCompleted() {
            if (mCurrentVisibleItemCount > 0 && mCurrentScrollState == SCROLL_STATE_IDLE) {
                if (mCellIsMobile && mIsMobileScrolling) {
                    handleMobileCellScroll();
                } else if (mIsWaitingForScrollFinish) {
                    touchEventsEnded();
                }
            }
        }

        /**
         * Determines if the listview scrolled up enough to reveal a new cell at the
         * top of the list. If so, then the appropriate parameters are updated.
         */
        public void checkAndHandleFirstVisibleCellChange() {
            if (mCurrentFirstVisibleItem != mPreviousFirstVisibleItem) {
                if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                    updateNeighborViewsForID(mMobileItemId);
                    handleCellSwitch();
                }
            }
        }

        /**
         * Determines if the listview scrolled down enough to reveal a new cell at the
         * bottom of the list. If so, then the appropriate parameters are updated.
         */
        public void checkAndHandleLastVisibleCellChange() {
            int currentLastVisibleItem = mCurrentFirstVisibleItem + mCurrentVisibleItemCount;
            int previousLastVisibleItem = mPreviousFirstVisibleItem + mPreviousVisibleItemCount;
            if (currentLastVisibleItem != previousLastVisibleItem) {
                if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                    updateNeighborViewsForID(mMobileItemId);
                    handleCellSwitch();
                }
            }
        }
    };
}

A teď nastává problém potřebuji Generický typ překonvertovat zase do daného typu pro určitý adapter, abych s ním mohl pracovat?

Ahoj, neni mi moc jasne o co se presne snazis ale prijde mi, ze pouzivas genericke typy na neco k cemu nejsou urcene.

Pro objasneni: kdyz pises neco genericky, tak je to vetsinou proto, ze ocekavas, ze dana implementace by se opakovala pro ruzne typy, takze to napises genericky, mas to v kodu jednou a pak to pouzivas na ruznych mistech a finalni typ se misto generickeho dosadi pri prekladu.

Prijde mi ponekud podivne zjistovat jakeho konrektniho typu je genericky typ, pokud opravdu neco takoveho potrebujes tak muzes pomoci instanceof zjistit jaky typ se tam aktualne pouziva ale tim zadratujes svou implementaci s konkretnim typem (typy) a uz to neni tak uplne genericke.

Myslim, ze by bylo mnohem lepsi kdyby jsi ve vsech "adapterech" podedil stejnou abstraktni tridu a presunul spolecny kod do teto tridy, pripadne pokud takovy kod neexistuje tak jen implementoval jeden interface (ani nemusi obsahovat zadne metody). Pak namisto generika tam budes pracovat s interfacem nebo abstraktni tridou a mas jistotu, ze tam budou jen hrusky/jabka, ktere implementuji ten interface a ne nejaka brambora.

Popis problému ještě jednou: Mám třídu CustomListView, které dědí z ListView. Rád bych udělal něco takového: dané třídě dám ArrayList<?> s daty potřebnými k vykreslení ListView, když bude uživatel přehazovat položky v seznamu, tak ona třída přehodí pouze prvky v arraylistu, s obsahem arraylistu vůbec nepracuje. poté pošle daný ArrayList<?> s daty do příslušného adaptéru, kde se data převedou na klasický např.: ArrayList<MenuItem> 

Tak jsem to vyřešil že třída pracuje pouze s indexy prvků a  poté zavolá metodu v adaptéru aby je tam přehodila tam a vykreslila. Nicméně díky :)