android Launcher源碼解析04：DeleteZone

       DeleteZone是launcher中比較簡單的一部分，其操作為

• 長按案頭上某個表徵圖後，會出現如下內容：1）dock欄消失；2）原dock欄位置出現一個垃圾箱圖案；
• 將該表徵圖拖動到垃圾箱位置後，會發現如下內容：1）垃圾箱表徵圖變為開啟；2）垃圾箱周圍出現一片紅色地區；3）表徵圖變為紅色；
• 將該表徵圖放到垃圾箱位置後，該表徵圖會被從案頭中刪除；

        查看DeleteZone的源碼，只要搞清楚了以上3個步驟是如何?的，那麼就理解了他的代碼了。 1）建構函式

public DeleteZone(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public DeleteZone(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);                final int srcColor = context.getResources().getColor(R.color.delete_color_filter);        mTrashPaint.setColorFilter(new PorterDuffColorFilter(srcColor, PorterDuff.Mode.SRC_ATOP));        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.DeleteZone, defStyle, 0);        mOrientation = a.getInt(R.styleable.DeleteZone_direction, ORIENTATION_HORIZONTAL);        a.recycle();    }    @Override    protected void onFinishInflate() {        super.onFinishInflate();        mTransition = (TransitionDrawable) getDrawable();    }

        這裡主要完成三項工作：1）構造對象；2）建立紅色地區的濾鏡顏色為紅色；3）判斷方向，這個是在launcher.xml中設定的方向。

    <com.xuxm.demo.launcher.DeleteZone        android:id="@+id/delete_zone"        android:layout_width="@dimen/delete_zone_size"        android:layout_height="@dimen/delete_zone_size"        android:paddingTop="@dimen/delete_zone_padding"        android:layout_gravity="top|center_horizontal"        android:scaleType="center"        android:src="@drawable/delete_zone_selector"        android:visibility="invisible"        launcher:direction="horizontal"        />

         同時需要注意到這裡的圖片並不是一張圖片，而是一個TransitionDrawable，其內容為：

<transition xmlns:android="http://schemas.android.com/apk/res/android">    <item android:drawable="@drawable/trashcan"  />    <item android:drawable="@drawable/trashcan_hover"  /></transition>

          這裡，他可以動態切換顯示的圖片，這也是你看到的垃圾箱關閉與開啟兩種顯示方式的根源。其實現在這幾個函數中實現：

   public void onDragEnter(DragSource source, int x, int y, int xOffset, int yOffset,            DragView dragView, Object dragInfo) {        mTransition.reverseTransition(TRANSITION_DURATION);        dragView.setPaint(mTrashPaint);    }    public void onDragOver(DragSource source, int x, int y, int xOffset, int yOffset,            DragView dragView, Object dragInfo) {    }    public void onDragExit(DragSource source, int x, int y, int xOffset, int yOffset,            DragView dragView, Object dragInfo) {        mTransition.reverseTransition(TRANSITION_DURATION);        dragView.setPaint(null);    }

        這裡，當被拖動表徵圖進入到DeleteZone地區時，表徵圖變為垃圾箱開啟中狀態，如果表徵圖離開了DeleteZone地區時，垃圾箱恢複為垃圾箱關閉狀態；dragView.setPaint(mTrashPaint);這一句是設定被拖動表徵圖顯示為紅色。

2）刪除表徵圖     當你將表徵圖放到垃圾箱地區後，就會刪除該表徵圖。這裡需要區別不同的表徵圖來源區域和不同的表徵圖類型，分別進行刪除。如果是對於檔案夾，需要先將檔案夾中的內容刪除，然後再刪除該檔案夾。

 public void onDrop(DragSource source, int x, int y, int xOffset, int yOffset,            DragView dragView, Object dragInfo) {        final ItemInfo item = (ItemInfo) dragInfo;        if (item.container == -1) return;        if (item.container == LauncherSettings.Favorites.CONTAINER_DESKTOP) {            if (item instanceof LauncherAppWidgetInfo) {                mLauncher.removeAppWidget((LauncherAppWidgetInfo) item);            }        } else {            if (source instanceof UserFolder) {                final UserFolder userFolder = (UserFolder) source;                final UserFolderInfo userFolderInfo = (UserFolderInfo) userFolder.getInfo();                // Item must be a ShortcutInfo otherwise it couldn't have been in the folder                // in the first place.                userFolderInfo.remove((ShortcutInfo)item);            }        }        if (item instanceof UserFolderInfo) {            final UserFolderInfo userFolderInfo = (UserFolderInfo)item;            LauncherModel.deleteUserFolderContentsFromDatabase(mLauncher, userFolderInfo);            mLauncher.removeFolder(userFolderInfo);        } else if (item instanceof LauncherAppWidgetInfo) {            final LauncherAppWidgetInfo launcherAppWidgetInfo = (LauncherAppWidgetInfo) item;            final LauncherAppWidgetHost appWidgetHost = mLauncher.getAppWidgetHost();            if (appWidgetHost != null) {                final int appWidgetId = launcherAppWidgetInfo.appWidgetId;                // Deleting an app widget ID is a void call but writes to disk before returning                // to the caller...                new Thread("deleteAppWidgetId") {                    public void run() {                        appWidgetHost.deleteAppWidgetId(launcherAppWidgetInfo.appWidgetId);                    }                }.start();            }        }        LauncherModel.deleteItemFromDatabase(mLauncher, item);    }

         之前在測試公司產品時，發現直接將表徵圖從檔案夾中直接拖動到垃圾箱刪除後，會發現檔案夾內顯示出現問題，究其原因就是未考慮到直接從檔案夾中刪除中的問題。

3）長按表徵圖開始拖動及結束拖動

public void onDragStart(DragSource source, Object info, int dragAction) {        final ItemInfo item = (ItemInfo) info;        if (item != null) {            mTrashMode = true;            createAnimations();            final int[] location = mLocation;            getLocationOnScreen(location);            /**             * mRight\mLeft\mBottom\mTop屬保護域，             * 需通過getRight()\getLeft()\getBottom()\getTop()來訪問             * modify by author             */            mRegion.set(location[0], location[1], location[0] + getRight() - getLeft(),                    location[1] + getBottom() - getTop());            mDragController.setDeleteRegion(mRegion);            mTransition.resetTransition();            startAnimation(mInAnimation);            mHandle.startAnimation(mHandleOutAnimation);            setVisibility(VISIBLE);        }    }

        之類首先獲得垃圾箱表徵圖的地區大小，據此設定DeleteZone位置的地區，同時初始化動畫對象createAnimations()。

    public void onDragEnd() {        if (mTrashMode) {            mTrashMode = false;            mDragController.setDeleteRegion(null);            startAnimation(mOutAnimation);            mHandle.startAnimation(mHandleInAnimation);            setVisibility(GONE);        }    }

        取消拖動地區效果，並且將dock欄回複，隱藏垃圾箱；4）初始化動畫

private void createAnimations() {        if (mInAnimation == null) {            mInAnimation = new FastAnimationSet();            final AnimationSet animationSet = mInAnimation;            animationSet.setInterpolator(new AccelerateInterpolator());            animationSet.addAnimation(new AlphaAnimation(0.0f, 1.0f));            if (mOrientation == ORIENTATION_HORIZONTAL) {                animationSet.addAnimation(new TranslateAnimation(Animation.ABSOLUTE, 0.0f,                        Animation.ABSOLUTE, 0.0f, Animation.RELATIVE_TO_SELF, 1.0f,                        Animation.RELATIVE_TO_SELF, 0.0f));            } else {                animationSet.addAnimation(new TranslateAnimation(Animation.RELATIVE_TO_SELF,                        1.0f, Animation.RELATIVE_TO_SELF, 0.0f, Animation.ABSOLUTE, 0.0f,                        Animation.ABSOLUTE, 0.0f));            }            animationSet.setDuration(ANIMATION_DURATION);        }        if (mHandleInAnimation == null) {            mHandleInAnimation = new AlphaAnimation(0.0f, 1.0f);            mHandleInAnimation.setDuration(ANIMATION_DURATION);        }        if (mOutAnimation == null) {            mOutAnimation = new FastAnimationSet();            final AnimationSet animationSet = mOutAnimation;            animationSet.setInterpolator(new AccelerateInterpolator());            animationSet.addAnimation(new AlphaAnimation(1.0f, 0.0f));            if (mOrientation == ORIENTATION_HORIZONTAL) {                animationSet.addAnimation(new FastTranslateAnimation(Animation.ABSOLUTE, 0.0f,                        Animation.ABSOLUTE, 0.0f, Animation.RELATIVE_TO_SELF, 0.0f,                        Animation.RELATIVE_TO_SELF, 1.0f));            } else {                animationSet.addAnimation(new FastTranslateAnimation(Animation.RELATIVE_TO_SELF,                        0.0f, Animation.RELATIVE_TO_SELF, 1.0f, Animation.ABSOLUTE, 0.0f,                        Animation.ABSOLUTE, 0.0f));            }            animationSet.setDuration(ANIMATION_DURATION);        }        if (mHandleOutAnimation == null) {            mHandleOutAnimation = new AlphaAnimation(1.0f, 0.0f);            mHandleOutAnimation.setFillAfter(true);            mHandleOutAnimation.setDuration(ANIMATION_DURATION);        }    }

        這裡主要設定三個動畫對象，dock隱藏動畫，mHandleInAnimation和mHandleOutAnimation；垃圾箱表徵圖動畫對象mInAnimation和mOutAnimation；

5)自訂Animation這裡自訂了兩個Animation，主要是重載了兩個函數，這兩個被重載的函數的功能如下：