DrawerLayout是android support包新增的側(cè)滑菜單控件感昼，在Android Studio中可以很方便的創(chuàng)建一個帶有側(cè)滑菜單的頁面澈缺。今天郎仆，我們來分析DrawerLayout它的實現(xiàn)原理蜀涨，來加深對它的了解瞎嬉。為了能讓讀者有一個清晰的認識和選擇性的了解，我在這里先列出本次分析的內(nèi)容概要厚柳，讀者可以按需了解氧枣。分析內(nèi)容為：
- 1.分析整體結(jié)構(gòu)，實現(xiàn)的功能性草娜。
- 2.分析包含的重點屬性挑胸，構(gòu)造方法初始化等。
- 3.分析布局實現(xiàn)宰闰，包括measure,layout,draw等茬贵。
- 4.分析觸摸事件，onTouchEvent,onInteceptTouchEvent等移袍。
- 5.分析LayoutParams的使用
- 6.分析SavedState解藻，用于備份還原狀態(tài)，備忘錄模式
- 7.由此總結(jié)葡盗，自定義一個View可能需要考慮實現(xiàn)哪些內(nèi)容螟左。
1.整體結(jié)構(gòu)，功能性分析
DrawerLayout相關(guān)的類及接口有如下：
- 1.類ViewDragHelper觅够，與DrawerLayout最緊密關(guān)系的類胶背。作為一個輔助類，它主要用于幫助DrawerLayout進行觸摸開啟喘先，關(guān)閉钳吟，拖動，釋放滑動等邏輯的判斷和處理窘拯，同時红且，還通過ViewDragHelper.Callback通知DrawerLayout狀態(tài)的一些變化坝茎。
- 2.類ViewDragCallback，ViewDragHelper.Callback接口的實現(xiàn)暇番，通過它可以使DrawerLayout和ViewDragHelper進行一些拖動等邏輯上的交互嗤放。
- 3.接口DrawerListener，提供對外回調(diào)的接口壁酬，用于監(jiān)聽onDrawerSlide（抽屜滑動）次酌，onDrawerOpened（抽屜打開），onDrawerClosed（抽屜關(guān)閉）厨喂，onDrawerStateChanged（抽屜狀態(tài)變化）等事件和措，以便外部能做出一些響應(yīng)庄呈。例如配合ToolBar蜕煌，實現(xiàn)側(cè)滑菜單時，更新ToolBar左側(cè)按鈕旋轉(zhuǎn)效果诬留。SimpleDrawerListener斜纪，接口DrawerListener的空實現(xiàn)，目的是可以通過它選擇性實現(xiàn)接口方法文兑，不會一次彈出那么多方法盒刚。
- 4.接口DrawerLayoutCompatImpl，定義DrawerLayout需要根據(jù)版本進行適配的接口绿贞。實現(xiàn)類分別有DrawerLayoutCompatImplBase和DrawerLayoutCompatImplApi21因块。版本21及以上，做的是布局內(nèi)容區(qū)域是否要填充到狀態(tài)欄籍铁，導(dǎo)航欄上涡上，實現(xiàn)沉浸式效果。版本21以下空實現(xiàn)拒名，因為系統(tǒng)不支持吩愧，所以不做處理。順便提下增显，這里采用了策略模式雁佳。
- 5.類SavedState，用于保存和恢復(fù)當前DrawerLayout狀態(tài)的類同云，實現(xiàn)Parcelable接口糖权，可實現(xiàn)數(shù)據(jù)序列化。配合onSaveInstanceState保存狀態(tài)數(shù)據(jù)炸站，onRestoreInstanceState恢復(fù)狀態(tài)數(shù)據(jù)星澳。這里采用了備忘錄模式，SavedState作為備忘者武契，DrawerLayout是備忘錄管理者募判，Activity是備忘錄使用者荡含。
- 6.類LayoutParams，自定義的ViewGroup.MarginLayoutParams届垫，通過它可以增加一些額外屬性的處理释液，這里有onScreen（劃出屏幕百分比），openState（開啟狀態(tài)）等装处。
- 7.類AccessibilityDelegate误债，輔助功能邏輯處理類，這里不做詳談妄迁。
2.重點屬性寝蹈，構(gòu)造方法初始化分析
- 1.包含三種狀態(tài)，STATE_IDLE（已打開或已關(guān)閉）登淘， STATE_DRAGGING（正在拖動）箫老， STATE_SETTLING（執(zhí)行打開或關(guān)閉的動畫過程中）。
- 2.包含四種鎖定模式黔州，LOCK_MODE_UNLOCKED（未鎖定耍鬓，用戶可以活動側(cè)滑）， LOCK_MODE_LOCKED_CLOSED（鎖定并關(guān)閉菜單流妻，用戶無法側(cè)滑牲蜀，但是程序調(diào)用可以實現(xiàn)側(cè)滑）， LOCK_MODE_LOCKED_OPEN（鎖定并打開菜單绅这，用戶無法側(cè)滑涣达，但是程序調(diào)用可以實現(xiàn)側(cè)滑）， LOCK_MODE_UNDEFINED（空白狀態(tài)证薇，初始狀態(tài)）度苔。
- 3.mLeftDragger，mRightDragger棕叫，用于處理左側(cè)和右側(cè)側(cè)滑的輔助類ViewDragHelper對象林螃。
- 4.mLeftCallback，mRightCallback俺泣，左側(cè)和右側(cè)側(cè)滑處理的回調(diào)接口疗认。
- 5.mShadowStart等各個方向側(cè)滑菜單陰影部分Drawable。
構(gòu)造方法分析
public DrawerLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
final float density = getResources().getDisplayMetrics().density;
mMinDrawerMargin = (int) (MIN_DRAWER_MARGIN * density + 0.5f);
final float minVel = MIN_FLING_VELOCITY * density;
//初始化左右拖動回調(diào)接口
mLeftCallback = new ViewDragCallback(Gravity.LEFT);
mRightCallback = new ViewDragCallback(Gravity.RIGHT);
//初始化左右拖動輔助類伏钠，并與拖動回調(diào)接口綁定横漏，設(shè)置當前方向拖動輔助對象可以觸發(fā)側(cè)滑的邊緣方向
mLeftDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mLeftCallback);
mLeftDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
mLeftDragger.setMinVelocity(minVel);
mLeftCallback.setDragger(mLeftDragger);
mRightDragger = ViewDragHelper.create(this, TOUCH_SLOP_SENSITIVITY, mRightCallback);
mRightDragger.setEdgeTrackingEnabled(ViewDragHelper.EDGE_RIGHT);
mRightDragger.setMinVelocity(minVel);
mRightCallback.setDragger(mRightDragger);
// 設(shè)置可獲取焦點，以便能捕獲返回鍵事件
setFocusableInTouchMode(true);
ViewCompat.setImportantForAccessibility(this,
ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_YES);
ViewCompat.setAccessibilityDelegate(this, new AccessibilityDelegate());
//設(shè)置不支持多點觸摸
ViewGroupCompat.setMotionEventSplittingEnabled(this, false);
//適配狀態(tài)欄區(qū)域顯示
if (ViewCompat.getFitsSystemWindows(this)) {
IMPL.configureApplyInsets(this);
mStatusBarBackground = IMPL.getDefaultStatusBarBackground(context);
}
mDrawerElevation = DRAWER_ELEVATION * density;
//里面非抽屜的子View列表
mNonDrawerViews = new ArrayList<View>();
}
3.布局實現(xiàn)分析
對于一個自定義View熟掂，它的布局實現(xiàn)和觸摸事件實現(xiàn)是它的核心功能缎浇。布局上一般需要實現(xiàn)測量，布局赴肚，繪制三個模塊素跺，在DrawerLayout中二蓝，實現(xiàn)了以下方法：
- onMeasure
- onLayout
- onDraw
- drawChild
onMeasure，根據(jù)父View傳遞過來的測量參數(shù)指厌，解析得到高度和寬度的測量模式刊愚，測量大小，這是父View提供的一個參考標準踩验，在DrawerLayout中鸥诽，測量模式只接受MeasureSpec.EXACTLY，也就是只接受確定的值箕憾，所以DrawerLayout的布局高度寬度屬性一般要設(shè)置為match_parent或者固定值牡借，而不能是wrap_conent，當然在編輯模式下除外袭异。所以DrawerLayout的測量大小設(shè)置了和父View一樣大小钠龙。然后針對所有子View，確定是否要適應(yīng)狀態(tài)欄區(qū)域扁远。然后區(qū)分內(nèi)容區(qū)域和側(cè)滑區(qū)域俊鱼，內(nèi)容區(qū)域完整填充DrawerLayout區(qū)域刻像，側(cè)滑區(qū)域根據(jù)相應(yīng)的規(guī)則測量畅买，目的使使側(cè)滑能占據(jù)DrawerLayout的一部分區(qū)域，既不能完全填充细睡，也不能完全沒顯示區(qū)域谷羞。
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
//默認，測量模式必須為EXACTLY
if (widthMode != MeasureSpec.EXACTLY || heightMode != MeasureSpec.EXACTLY) {
if (isInEditMode()) {
//編輯模式下溜徙，針對非EXACTLY 模式做的一些適配
}
} else {
throw new IllegalArgumentException(
"DrawerLayout must be measured with MeasureSpec.EXACTLY.");
}
}
//設(shè)置最終DrawerLayout的測量大小
setMeasuredDimension(widthSize, heightSize);
final boolean applyInsets = mLastInsets != null && ViewCompat.getFitsSystemWindows(this);
final int layoutDirection = ViewCompat.getLayoutDirection(this);
// Only one drawer is permitted along each vertical edge (left / right). These two booleans
// are tracking the presence of the edge drawers.
boolean hasDrawerOnLeftEdge = false;
boolean hasDrawerOnRightEdge = false;
final int childCount = getChildCount();
//對所有子View進行測量
for (int i = 0; i < childCount; i++) {
final View child = getChildAt(i);
if (child.getVisibility() == GONE) {
continue;
}
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
//是否適配狀態(tài)欄區(qū)域
if (applyInsets) {
final int cgrav = GravityCompat.getAbsoluteGravity(lp.gravity, layoutDirection);
if (ViewCompat.getFitsSystemWindows(child)) {
IMPL.dispatchChildInsets(child, mLastInsets, cgrav);
} else {
IMPL.applyMarginInsets(lp, mLastInsets, cgrav);
}
}
if (isContentView(child)) {
//內(nèi)容區(qū)域湃缎，完整填充DrawerLayout
// Content views get measured at exactly the layout's size.
final int contentWidthSpec = MeasureSpec.makeMeasureSpec(
widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
final int contentHeightSpec = MeasureSpec.makeMeasureSpec(
heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);
child.measure(contentWidthSpec, contentHeightSpec);
} else if (isDrawerView(child)) {
//側(cè)滑區(qū)域，設(shè)置陰影效果
if (SET_DRAWER_SHADOW_FROM_ELEVATION) {
if (ViewCompat.getElevation(child) != mDrawerElevation) {
ViewCompat.setElevation(child, mDrawerElevation);
}
}
final @EdgeGravity int childGravity =
getDrawerViewAbsoluteGravity(child) & Gravity.HORIZONTAL_GRAVITY_MASK;
// Note that the isDrawerView check guarantees that childGravity here is either
// LEFT or RIGHT
boolean isLeftEdgeDrawer = (childGravity == Gravity.LEFT);
if ((isLeftEdgeDrawer && hasDrawerOnLeftEdge)
|| (!isLeftEdgeDrawer && hasDrawerOnRightEdge)) {
throw new IllegalStateException("Child drawer has absolute gravity "
+ gravityToString(childGravity) + " but this " + TAG + " already has a "
+ "drawer view along that edge");
}
if (isLeftEdgeDrawer) {
hasDrawerOnLeftEdge = true;
} else {
hasDrawerOnRightEdge = true;
}
//計算側(cè)滑的寬高的測量值蠢壹，并對側(cè)滑區(qū)域進行測量
final int drawerWidthSpec = getChildMeasureSpec(widthMeasureSpec,
mMinDrawerMargin + lp.leftMargin + lp.rightMargin,
lp.width);
final int drawerHeightSpec = getChildMeasureSpec(heightMeasureSpec,
lp.topMargin + lp.bottomMargin,
lp.height);
child.measure(drawerWidthSpec, drawerHeightSpec);
} else {
throw new IllegalStateException("Child " + child + " at index " + i
+ " does not have a valid layout_gravity - must be Gravity.LEFT, "
+ "Gravity.RIGHT or Gravity.NO_GRAVITY");
}
}
}
所以總結(jié)測量的結(jié)果就是嗓违，DrawerLayout的大小完整填充父View，內(nèi)容區(qū)域完整填充DrawerLayout图贸，側(cè)滑區(qū)域?qū)挾壬喜糠痔畛漉寮荆叨壬峡赏暾畛浠虿糠痔畛洹?/p>
onLayout，對所有子View疏日，如果是內(nèi)容區(qū)域偿洁，根據(jù)測量結(jié)果進行布局，如果是側(cè)滑區(qū)域沟优，那就要區(qū)分是左側(cè)側(cè)滑還是右側(cè)側(cè)滑涕滋，這里分析左側(cè)側(cè)滑，根據(jù)當前子View的LayoutParams參數(shù)的gravity屬性挠阁，在高度上分為頂部對齊宾肺，底部對齊溯饵，居中顯示三種，在寬度上锨用，根據(jù)LayoutParams參數(shù)的onScreen（側(cè)滑顯示在屏幕上的百分比）瓣喊，將側(cè)滑布局到完全收起到完全劃出之間。
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
mInLayout = true;
final int width = r - l;
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
final View child = getChildAt(i);
//隱藏的子View不考慮布局
if (child.getVisibility() == GONE) {
continue;
}
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
if (isContentView(child)) {
//內(nèi)容區(qū)域布局
child.layout(lp.leftMargin, lp.topMargin,
lp.leftMargin + child.getMeasuredWidth(),
lp.topMargin + child.getMeasuredHeight());
} else { // Drawer, if it wasn't onMeasure would have thrown an exception.
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight();
int childLeft;
//計算側(cè)滑顯示到屏幕的寬度百分比
final float newOffset;
if (checkDrawerViewAbsoluteGravity(child, Gravity.LEFT)) {
childLeft = -childWidth + (int) (childWidth * lp.onScreen);
newOffset = (float) (childWidth + childLeft) / childWidth;
} else { // Right; onMeasure checked for us.
childLeft = width - (int) (childWidth * lp.onScreen);
newOffset = (float) (width - childLeft) / childWidth;
}
final boolean changeOffset = newOffset != lp.onScreen;
final int vgrav = lp.gravity & Gravity.VERTICAL_GRAVITY_MASK;
//區(qū)分頂部對齊黔酥，底部對齊藻三，居中對齊布局
switch (vgrav) {
default:
case Gravity.TOP: {
child.layout(childLeft, lp.topMargin, childLeft + childWidth,
lp.topMargin + childHeight);
break;
}
case Gravity.BOTTOM: {
final int height = b - t;
child.layout(childLeft,
height - lp.bottomMargin - child.getMeasuredHeight(),
childLeft + childWidth,
height - lp.bottomMargin);
break;
}
case Gravity.CENTER_VERTICAL: {
final int height = b - t;
int childTop = (height - childHeight) / 2;
// Offset for margins. If things don't fit right because of
// bad measurement before, oh well.
if (childTop < lp.topMargin) {
childTop = lp.topMargin;
} else if (childTop + childHeight > height - lp.bottomMargin) {
childTop = height - lp.bottomMargin - childHeight;
}
child.layout(childLeft, childTop, childLeft + childWidth,
childTop + childHeight);
break;
}
}
if (changeOffset) {
//側(cè)滑過程中统捶，通知更新布局參數(shù)的onScreen屬性乾蓬，并通知監(jiān)聽葛作，側(cè)滑滑動中
setDrawerViewOffset(child, newOffset);
}
//側(cè)滑沒有劃出屏幕時活烙，設(shè)置為不可見帽芽，這樣后面就避免無效繪制了
final int newVisibility = lp.onScreen > 0 ? VISIBLE : INVISIBLE;
if (child.getVisibility() != newVisibility) {
child.setVisibility(newVisibility);
}
}
}
mInLayout = false;
mFirstLayout = false;
}
onDraw稿茉，接下來開始繪制颅夺，這個很簡單箕宙，因為作為一個容器忘衍，本身不需要繪制什么內(nèi)容逾苫，這里根據(jù)版本適配，做了繪制狀態(tài)欄顏色的工作枚钓。
@Override
public void onDraw(Canvas c) {
super.onDraw(c);
//如果需要繪制狀態(tài)欄铅搓，并且狀態(tài)欄背景drawable不為空即21以上版本，就進行狀態(tài)欄區(qū)域的繪制
if (mDrawStatusBarBackground && mStatusBarBackground != null) {
final int inset = IMPL.getTopInset(mLastInsets);
if (inset > 0) {
mStatusBarBackground.setBounds(0, 0, getWidth(), inset);
mStatusBarBackground.draw(c);
}
}
}
drawChild搀捷，接下來是繪制具體的某個子View星掰，首先繪制內(nèi)容區(qū)域，為了提高繪制效率嫩舟，如果側(cè)滑劃出時氢烘，那么被側(cè)滑遮擋的區(qū)域就不需要繪制了，只裁剪繪制需要顯示出來的那部分家厌。然后判斷是否繪制覆蓋在內(nèi)容區(qū)域上陰影區(qū)域播玖，如果不顯示內(nèi)容上層陰影，則判斷是否繪制左側(cè)或者右側(cè)的側(cè)邊陰影饭于。
@Override
protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
final int height = getHeight();
final boolean drawingContent = isContentView(child);
int clipLeft = 0, clipRight = getWidth();
//裁剪區(qū)域繪制內(nèi)容區(qū)域
final int restoreCount = canvas.save();
if (drawingContent) {
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
final View v = getChildAt(i);
if (v == child || v.getVisibility() != VISIBLE
|| !hasOpaqueBackground(v) || !isDrawerView(v)
|| v.getHeight() < height) {
continue;
}
if (checkDrawerViewAbsoluteGravity(v, Gravity.LEFT)) {
final int vright = v.getRight();
if (vright > clipLeft) clipLeft = vright;
} else {
final int vleft = v.getLeft();
if (vleft < clipRight) clipRight = vleft;
}
}
canvas.clipRect(clipLeft, 0, clipRight, getHeight());
}
final boolean result = super.drawChild(canvas, child, drawingTime);
canvas.restoreToCount(restoreCount);
if (mScrimOpacity > 0 && drawingContent) {
//繪制內(nèi)容區(qū)域上層的陰影區(qū)域蜀踏，一般劃出了就會顯示
final int baseAlpha = (mScrimColor & 0xff000000) >>> 24;
final int imag = (int) (baseAlpha * mScrimOpacity);
final int color = imag << 24 | (mScrimColor & 0xffffff);
mScrimPaint.setColor(color);
canvas.drawRect(clipLeft, 0, clipRight, getHeight(), mScrimPaint);
} else if (mShadowLeftResolved != null
&& checkDrawerViewAbsoluteGravity(child, Gravity.LEFT)) {
//繪制左側(cè)側(cè)滑欄的陰影部分，根據(jù)滑動距離調(diào)整陰影透明度
final int shadowWidth = mShadowLeftResolved.getIntrinsicWidth();
final int childRight = child.getRight();
final int drawerPeekDistance = mLeftDragger.getEdgeSize();
final float alpha =
Math.max(0, Math.min((float) childRight / drawerPeekDistance, 1.f));
mShadowLeftResolved.setBounds(childRight, child.getTop(),
childRight + shadowWidth, child.getBottom());
mShadowLeftResolved.setAlpha((int) (0xff * alpha));
mShadowLeftResolved.draw(canvas);
} else if (mShadowRightResolved != null
&& checkDrawerViewAbsoluteGravity(child, Gravity.RIGHT)) {
//繪制右側(cè)側(cè)滑欄的陰影部分镰绎，根據(jù)滑動距離調(diào)整陰影透明度
final int shadowWidth = mShadowRightResolved.getIntrinsicWidth();
final int childLeft = child.getLeft();
final int showing = getWidth() - childLeft;
final int drawerPeekDistance = mRightDragger.getEdgeSize();
final float alpha =
Math.max(0, Math.min((float) showing / drawerPeekDistance, 1.f));
mShadowRightResolved.setBounds(childLeft - shadowWidth, child.getTop(),
childLeft, child.getBottom());
mShadowRightResolved.setAlpha((int) (0xff * alpha));
mShadowRightResolved.draw(canvas);
}
return result;
}
4.觸摸事件分析
DrawerLayout實現(xiàn)了onInterceptTouchEvent和onTouchEvent方法脓斩，onInterceptTouchEvent處理TouchEvent事件的攔截，如果左側(cè)或者右側(cè)ViewDragHelper對象要攔截畴栖，或者是側(cè)滑菜單顯示時随静，點擊位置在內(nèi)容區(qū)域，或者側(cè)滑欄正在執(zhí)行移動動畫，或者取消子View的Touch操作燎猛，就會攔截恋捆，這樣子View就無法接收Touch事件了。
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = MotionEventCompat.getActionMasked(ev);
// "|" used deliberately here; both methods should be invoked.
final boolean interceptForDrag = mLeftDragger.shouldInterceptTouchEvent(ev)
| mRightDragger.shouldInterceptTouchEvent(ev);
boolean interceptForTap = false;
switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mInitialMotionX = x;
mInitialMotionY = y;
if (mScrimOpacity > 0) {
final View child = mLeftDragger.findTopChildUnder((int) x, (int) y);
if (child != null && isContentView(child)) {
interceptForTap = true;
}
}
mDisallowInterceptRequested = false;
mChildrenCanceledTouch = false;
break;
}
case MotionEvent.ACTION_MOVE: {
// If we cross the touch slop, don't perform the delayed peek for an edge touch.
if (mLeftDragger.checkTouchSlop(ViewDragHelper.DIRECTION_ALL)) {
mLeftCallback.removeCallbacks();
mRightCallback.removeCallbacks();
}
break;
}
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP: {
closeDrawers(true);
mDisallowInterceptRequested = false;
mChildrenCanceledTouch = false;
}
}
return interceptForDrag || interceptForTap || hasPeekingDrawer() || mChildrenCanceledTouch;
}
onTouchEvent方法重绷，會將Touch事件交給左沸停，右ViewDragHelper對象幫助處理，然后自己還實現(xiàn)了發(fā)生ACTION_UP和ACTION_CANCEL時昭卓，關(guān)閉側(cè)滑欄的操作愤钾。
@Override
public boolean onTouchEvent(MotionEvent ev) {
//將Touch事件交給ViewDragHelper對象處理
mLeftDragger.processTouchEvent(ev);
mRightDragger.processTouchEvent(ev);
final int action = ev.getAction();
boolean wantTouchEvents = true;
//后面處理ACTION_UP和ACTION_CANCEL時，關(guān)閉側(cè)滑欄的操作
switch (action & MotionEventCompat.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mInitialMotionX = x;
mInitialMotionY = y;
mDisallowInterceptRequested = false;
mChildrenCanceledTouch = false;
break;
}
case MotionEvent.ACTION_UP: {
final float x = ev.getX();
final float y = ev.getY();
boolean peekingOnly = true;
final View touchedView = mLeftDragger.findTopChildUnder((int) x, (int) y);
if (touchedView != null && isContentView(touchedView)) {
final float dx = x - mInitialMotionX;
final float dy = y - mInitialMotionY;
final int slop = mLeftDragger.getTouchSlop();
if (dx * dx + dy * dy < slop * slop) {
// Taps close a dimmed open drawer but only if it isn't locked open.
final View openDrawer = findOpenDrawer();
if (openDrawer != null) {
peekingOnly = getDrawerLockMode(openDrawer) == LOCK_MODE_LOCKED_OPEN;
}
}
}
closeDrawers(peekingOnly);
mDisallowInterceptRequested = false;
break;
}
case MotionEvent.ACTION_CANCEL: {
closeDrawers(true);
mDisallowInterceptRequested = false;
mChildrenCanceledTouch = false;
break;
}
}
return wantTouchEvents;
}
DrawerLayout把絕大部分的觸摸事件交給ViewDragHelper去處理候醒，那么在ViewDragHelper中是怎么處理的呢能颁？我們看看processTouchEvent
public void processTouchEvent(MotionEvent ev) {
//取得當前Touch的action 和action 序號
final int action = MotionEventCompat.getActionMasked(ev);
final int actionIndex = MotionEventCompat.getActionIndex(ev);
//down事件的話，執(zhí)行cancel倒淫，重置一些記錄Touch事件的對象數(shù)據(jù)伙菊，為后面處理Touch事件做初始化準備
if (action == MotionEvent.ACTION_DOWN) {
// Reset things for a new event stream, just in case we didn't get
// the whole previous stream.
cancel();
}
//添加觸摸力度跟蹤對象，為后期計算滑動速度檢測做準備敌土，這里這個對象的獲取采用享元模式镜硕，避免頻繁創(chuàng)建銷毀對象
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
final int pointerId = ev.getPointerId(0);
//這里找到當前觸摸點的最頂層的子View,作為需要操作的View
final View toCapture = findTopChildUnder((int) x, (int) y);
//保存當前Touch點發(fā)生的初始狀態(tài)
saveInitialMotion(x, y, pointerId);
//這里是點在一個正在滑動的側(cè)滑欄上，使側(cè)滑欄的狀態(tài)由正在滑動狀態(tài)變?yōu)檎谕蟿訝顟B(tài)
// Since the parent is already directly processing this touch event,
// there is no reason to delay for a slop before dragging.
// Start immediately if possible.
tryCaptureViewForDrag(toCapture, pointerId);
//這里處理側(cè)滑欄的觸摸觸發(fā)區(qū)域是否觸摸了返干，如果側(cè)滑欄邊緣觸摸了兴枯，則通知回調(diào)，那么DrawerLayout里就會處理它犬金，執(zhí)行一個側(cè)滑微彈的操作念恍，也就是稍微彈出一點，表示觸發(fā)了側(cè)滑操作
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
break;
}
case MotionEventCompat.ACTION_POINTER_DOWN: {
final int pointerId = ev.getPointerId(actionIndex);
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
//保存當前Touch點發(fā)生的初始狀態(tài)
saveInitialMotion(x, y, pointerId);
//嘗試去觸發(fā)拖動操作
// A ViewDragHelper can only manipulate one view at a time.
if (mDragState == STATE_IDLE) {
// If we're idle we can do anything! Treat it like a normal down event.
final View toCapture = findTopChildUnder((int) x, (int) y);
tryCaptureViewForDrag(toCapture, pointerId);
final int edgesTouched = mInitialEdgesTouched[pointerId];
if ((edgesTouched & mTrackingEdges) != 0) {
mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
}
} else if (isCapturedViewUnder((int) x, (int) y)) {
// We're still tracking a captured view. If the same view is under this
// point, we'll swap to controlling it with this pointer instead.
// (This will still work if we're "catching" a settling view.)
tryCaptureViewForDrag(mCapturedView, pointerId);
}
break;
}
case MotionEvent.ACTION_MOVE: {
if (mDragState == STATE_DRAGGING) {
// If pointer is invalid then skip the ACTION_MOVE.
if (!isValidPointerForActionMove(mActivePointerId)) break;
final int index = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(index);
final float y = ev.getY(index);
final int idx = (int) (x - mLastMotionX[mActivePointerId]);
final int idy = (int) (y - mLastMotionY[mActivePointerId]);
//正在拖動時晚顷，更新側(cè)滑欄拖動的位置
dragTo(mCapturedView.getLeft() + idx, mCapturedView.getTop() + idy, idx, idy);
saveLastMotion(ev);
} else {
// Check to see if any pointer is now over a draggable view.
final int pointerCount = ev.getPointerCount();
for (int i = 0; i < pointerCount; i++) {
final int pointerId = ev.getPointerId(i);
// If pointer is invalid then skip the ACTION_MOVE.
if (!isValidPointerForActionMove(pointerId)) continue;
//否則，判斷事件是否正在側(cè)滑邊緣移動疗疟，以嘗試去觸發(fā)側(cè)滑欄拖動操作
final float x = ev.getX(i);
final float y = ev.getY(i);
final float dx = x - mInitialMotionX[pointerId];
final float dy = y - mInitialMotionY[pointerId];
reportNewEdgeDrags(dx, dy, pointerId);
if (mDragState == STATE_DRAGGING) {
// Callback might have started an edge drag.
break;
}
final View toCapture = findTopChildUnder((int) x, (int) y);
if (checkTouchSlop(toCapture, dx, dy)
&& tryCaptureViewForDrag(toCapture, pointerId)) {
break;
}
}
saveLastMotion(ev);
}
break;
}
case MotionEventCompat.ACTION_POINTER_UP: {
final int pointerId = ev.getPointerId(actionIndex);
if (mDragState == STATE_DRAGGING && pointerId == mActivePointerId) {
// Try to find another pointer that's still holding on to the captured view.
int newActivePointer = INVALID_POINTER;
final int pointerCount = ev.getPointerCount();
for (int i = 0; i < pointerCount; i++) {
final int id = ev.getPointerId(i);
if (id == mActivePointerId) {
// This one's going away, skip.
continue;
}
//在拖動狀態(tài)下该默，嘗試去尋找當前的新的Touch點是否觸發(fā)側(cè)滑拖動操作
final float x = ev.getX(i);
final float y = ev.getY(i);
if (findTopChildUnder((int) x, (int) y) == mCapturedView
&& tryCaptureViewForDrag(mCapturedView, id)) {
newActivePointer = mActivePointerId;
break;
}
}
//如果當前這個Touch點沒有成功觸發(fā)側(cè)滑拖動操作，就去釋放這個正在拖動的View
if (newActivePointer == INVALID_POINTER) {
// We didn't find another pointer still touching the view, release it.
releaseViewForPointerUp();
}
}
clearMotionHistory(pointerId);
break;
}
case MotionEvent.ACTION_UP: {
//up和cancel事件發(fā)生時策彤，釋放這個正在拖動的View
if (mDragState == STATE_DRAGGING) {
releaseViewForPointerUp();
}
cancel();
break;
}
case MotionEvent.ACTION_CANCEL: {
if (mDragState == STATE_DRAGGING) {
dispatchViewReleased(0, 0);
}
cancel();
break;
}
}
}
此外還有shouldInterceptTouchEvent這個輔助攔截事件栓袖，實現(xiàn)上和processTouchEvent差不多，大家可以自行分析店诗。
總結(jié)觸摸事件的處理裹刮，判斷是否觸摸在可觸發(fā)側(cè)滑欄的區(qū)域，未彈出時庞瘸，根據(jù)滑動的力度判斷是否彈出側(cè)滑捧弃，在側(cè)滑彈出的過程中，正在拖動側(cè)滑的過程，已經(jīng)滑出后等狀態(tài)時违霞，的一些觸摸事件的處理嘴办。
5.自定義LayoutParams分析，通過自定義LayoutParams买鸽，可以為子View提供一些額外的布局參數(shù)涧郊。實現(xiàn)如下。
public static class LayoutParams extends ViewGroup.MarginLayoutParams {
private static final int FLAG_IS_OPENED = 0x1;
private static final int FLAG_IS_OPENING = 0x2;
private static final int FLAG_IS_CLOSING = 0x4;
//額外處理了眼五，gravity（靠邊方向）妆艘，onScreen（顯示出屏幕的百分比），isPeeking（是否正在微彈）看幼，openState（打開狀態(tài)）
public int gravity = Gravity.NO_GRAVITY;
float onScreen;
boolean isPeeking;
int openState;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
final TypedArray a = c.obtainStyledAttributes(attrs, LAYOUT_ATTRS);
this.gravity = a.getInt(0, Gravity.NO_GRAVITY);
a.recycle();
}
public LayoutParams(int width, int height) {
super(width, height);
}
public LayoutParams(int width, int height, int gravity) {
this(width, height);
this.gravity = gravity;
}
public LayoutParams(LayoutParams source) {
super(source);
this.gravity = source.gravity;
}
public LayoutParams(ViewGroup.LayoutParams source) {
super(source);
}
public LayoutParams(ViewGroup.MarginLayoutParams source) {
super(source);
}
}
那么它是在哪里生效的呢?是DrawerLayout復(fù)寫了ViewGroup的generateLayoutParams方法双仍，在這里提供了自己的LayoutParams
@Override
protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
}
@Override
protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams
? new LayoutParams((LayoutParams) p)
: p instanceof ViewGroup.MarginLayoutParams
? new LayoutParams((MarginLayoutParams) p)
: new LayoutParams(p);
}
而generateLayoutParams是在ViewGroup的addView方法中調(diào)用的
public void addView(View child, int index) {
if (child == null) {
throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup");
}
LayoutParams params = child.getLayoutParams();
if (params == null) {
//此處調(diào)用了generateDefaultLayoutParams
params = generateDefaultLayoutParams();
if (params == null) {
throw new IllegalArgumentException("generateDefaultLayoutParams() cannot return null");
}
}
addView(child, index, params);
}
public void addView(View child, int width, int height) {
//此處調(diào)用了generateDefaultLayoutParams
final LayoutParams params = generateDefaultLayoutParams();
params.width = width;
params.height = height;
addView(child, -1, params);
}
看到這里，我們就明白我們自定義的LayoutParams是怎么生效的了桌吃。
6.SaveState分析
SavedState用于保存和恢復(fù)DrawerLayout的狀態(tài)朱沃，SavedState實現(xiàn)Parcelable接口,可實現(xiàn)數(shù)據(jù)的序列化。這里是一種備忘錄模式茅诱，SavedState作為備忘者逗物，DrawerLayout是備忘錄管理者，Activity是備忘錄使用者瑟俭。那么我們看看使用SavedState的實現(xiàn)
@Override
protected Parcelable onSaveInstanceState() {
//這里是保存狀態(tài)翎卓，系統(tǒng)在需要保存該狀態(tài)時會調(diào)用該方法，在這里初始化SavedState摆寄，將要保存的數(shù)據(jù)集合起來
final Parcelable superState = super.onSaveInstanceState();
final SavedState ss = new SavedState(superState);
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
final View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
// Is the current child fully opened (that is, not closing)?
boolean isOpenedAndNotClosing = (lp.openState == LayoutParams.FLAG_IS_OPENED);
// Is the current child opening?
boolean isClosedAndOpening = (lp.openState == LayoutParams.FLAG_IS_OPENING);
if (isOpenedAndNotClosing || isClosedAndOpening) {
// If one of the conditions above holds, save the child's gravity
// so that we open that child during state restore.
ss.openDrawerGravity = lp.gravity;
break;
}
}
ss.lockModeLeft = mLockModeLeft;
ss.lockModeRight = mLockModeRight;
ss.lockModeStart = mLockModeStart;
ss.lockModeEnd = mLockModeEnd;
return ss;
}
下面看看恢復(fù)數(shù)據(jù)的地方
@Override
protected void onRestoreInstanceState(Parcelable state) {
if (!(state instanceof SavedState)) {
super.onRestoreInstanceState(state);
return;
}
//先恢復(fù)非SavedState 的數(shù)據(jù)
final SavedState ss = (SavedState) state;
super.onRestoreInstanceState(ss.getSuperState());
//后面再根據(jù)SavedState 存儲的數(shù)據(jù)失暴，恢復(fù)相應(yīng)的狀態(tài)
if (ss.openDrawerGravity != Gravity.NO_GRAVITY) {
final View toOpen = findDrawerWithGravity(ss.openDrawerGravity);
if (toOpen != null) {
openDrawer(toOpen);
}
}
if (ss.lockModeLeft != LOCK_MODE_UNDEFINED) {
setDrawerLockMode(ss.lockModeLeft, Gravity.LEFT);
}
if (ss.lockModeRight != LOCK_MODE_UNDEFINED) {
setDrawerLockMode(ss.lockModeRight, Gravity.RIGHT);
}
if (ss.lockModeStart != LOCK_MODE_UNDEFINED) {
setDrawerLockMode(ss.lockModeStart, GravityCompat.START);
}
if (ss.lockModeEnd != LOCK_MODE_UNDEFINED) {
setDrawerLockMode(ss.lockModeEnd, GravityCompat.END);
}
}
7.實現(xiàn)總結(jié)
分析完DrawerLayout之后，我們總結(jié)自定義一個View可能需要的實現(xiàn)有微饥，測量逗扒，布局，繪制欠橘，事件分發(fā)處理矩肩，事件攔截處理，自身事件處理肃续，自定義LayoutParams黍檩，考慮更多的話，有狀態(tài)的存儲恢復(fù)始锚，輔助功能狀態(tài)下的事件處理刽酱，當然，還有重要的自身的邏輯處理瞧捌。
我們也看到DrawerLayout這個View本身只是一個控制側(cè)滑顯示的容器棵里，一般我們會有如下的方式使用它。
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start"
>
<include
layout="@layout/app_bar_main2"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main2"
app:menu="@menu/activity_main2_drawer"
/>
</android.support.v4.widget.DrawerLayout>
include的部分就是內(nèi)容部分，而側(cè)滑部分就是NavigationView了衍慎，為什么判斷它是側(cè)滑部分转唉，是看其中定義的 android:layout_gravity="start"，DrawerLayout會認定它就是側(cè)滑部分稳捆。
顯然DrawerLayout并沒有完全實現(xiàn)我們想要的側(cè)滑菜單赠法，因為里面我們并沒有看到側(cè)滑的內(nèi)容。后面我將分析NavigationView的實現(xiàn)乔夯。
