2011.06.21（3）——— android 1.6 launcher研究之Drag&Drop模型-优快云博客

本文介绍了Android 1.6 Launcher中的Drag & Drop模型，包括DragLayer、DragController等关键类的作用及交互流程，深入探讨了拖拽操作的实现细节。

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2011.06.21（3）——— android 1.6 launcher研究之Drag&Drop模型
参考：[url]http://blog.youkuaiyun.com/stonecao/archive/2011/06/02/6462357.aspx[/url]
[url]http://blog.youkuaiyun.com/hmg25/archive/2011/03/02/6217659.aspx[/url]

研究了launcher的拖拽模型里面重要的类如下：

DragLayer：

public class DragLayer extends FrameLayout implements DragController {

}

DragController：


/*
 * Copyright (C) 2008 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/licenses/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.lp.launcher;

import android.view.View;

/**
 * Interface for initiating a drag within a view or across multiple views.
 *
 */
public interface DragController {

    /**
     * Interface to receive notifications when a drag starts or stops
     */
    interface DragListener {

        /**
         * A drag has begun
         * 
         * @param v The view that is being dragged
         * @param source An object representing where the drag originated
         * @param info The data associated with the object that is being dragged
         * @param dragAction The drag action: either {@link DragController#DRAG_ACTION_MOVE}
         *        or {@link DragController#DRAG_ACTION_COPY}
         */
        void onDragStart(View v, DragSource source, Object info, int dragAction);

        /**
         * The drag has eneded
         */
        void onDragEnd();
    }

    /**
     * Indicates the drag is a move.
     */
    public static int DRAG_ACTION_MOVE = 0;

    /**
     * Indicates the drag is a copy.
     */
    public static int DRAG_ACTION_COPY = 1;

    /**
     * Starts a drag
     * 
     * @param v The view that is being dragged
     * @param source An object representing where the drag originated
     * @param info The data associated with the object that is being dragged
     * @param dragAction The drag action: either {@link #DRAG_ACTION_MOVE} or
     *        {@link #DRAG_ACTION_COPY}
     */
    void startDrag(View v, DragSource source, Object info, int dragAction);

    /**
     * Sets the drag listner which will be notified when a drag starts or ends.
     */
    void setDragListener(DragListener l);

    /**
     * Remove a previously installed drag listener.
     */
    void removeDragListener(DragListener l);
}

DragSource：


/*
 * Copyright (C) 2008 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/licenses/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.lp.launcher;

import android.view.View;

/**
 * Interface defining an object that can originate a drag.
 *
 */
public interface DragSource {
    void setDragger(DragController dragger);
    void onDropCompleted(View target, boolean success);
}

DropTarget：


/*
 * Copyright (C) 2008 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/licenses/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.lp.launcher;

import android.graphics.Rect;

/**
 * Interface defining an object that can receive a drag.
 *
 */
public interface DropTarget {

    /**
     * Handle an object being dropped on the DropTarget
     * 
     * @param source DragSource where the drag started
     * @param x X coordinate of the drop location
     * @param y Y coordinate of the drop location
     * @param xOffset Horizontal offset with the object being dragged where the original touch happened
     * @param yOffset Vertical offset with the object being dragged where the original touch happened
     * @param dragInfo Data associated with the object being dragged
     * 
     */
    void onDrop(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo);

    void onDragEnter(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo);

    void onDragOver(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo);

    void onDragExit(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo);

    /**
     * Check if a drop action can occur at, or near, the requested location.
     * This may be called repeatedly during a drag, so any calls should return
     * quickly.
     * 
     * @param source DragSource where the drag started
     * @param x X coordinate of the drop location
     * @param y Y coordinate of the drop location
     * @param xOffset Horizontal offset with the object being dragged where the
     *            original touch happened
     * @param yOffset Vertical offset with the object being dragged where the
     *            original touch happened
     * @param dragInfo Data associated with the object being dragged
     * @return True if the drop will be accepted, false otherwise.
     */
    boolean acceptDrop(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo);

    /**
     * Estimate the surface area where this object would land if dropped at the
     * given location.
     * 
     * @param source DragSource where the drag started
     * @param x X coordinate of the drop location
     * @param y Y coordinate of the drop location
     * @param xOffset Horizontal offset with the object being dragged where the
     *            original touch happened
     * @param yOffset Vertical offset with the object being dragged where the
     *            original touch happened
     * @param dragInfo Data associated with the object being dragged
     * @param recycle {@link Rect} object to be possibly recycled.
     * @return Estimated area that would be occupied if object was dropped at
     *         the given location. Should return null if no estimate is found,
     *         or if this target doesn't provide estimations.
     */
    Rect estimateDropLocation(DragSource source, int x, int y, int xOffset, int yOffset, Object dragInfo, Rect recycle);
}