編輯:關於Android編程
當一個Touch事件發生,系統首先把事件傳遞給當前的Activity,由Activity的dispatchTouchEvent分發事件,源碼如下:
public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }Down事件發生時會進入一個onUserInteraction()方法,點進去可以看到這是一個空方法,我們可以根據需求重寫該方法。
getWindow().superDispatchTouchEvent(ev)調用Window的superDispatchTouchEvent方法分發事件,而Window的實現是PhoneWindow,所以是調用PhoneWindow的superDispatchTouchEvent派發事件,在這裡面就是將事件從最外層向裡逐級派發。如果返回false,也就是事件沒有消耗,會執行下面的onTouchEvent
下面就看看ViewGroup裡面的事件派發
@Override public boolean dispatchTouchEvent(MotionEvent ev) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(ev, 1); } // If the event targets the accessibility focused view and this is it, start // normal event dispatch. Maybe a descendant is what will handle the click. if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) { ev.setTargetAccessibilityFocus(false); } boolean handled = false; if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; // Handle an initial down. if (actionMasked == MotionEvent.ACTION_DOWN) { // Throw away all previous state when starting a new touch gesture. // The framework may have dropped the up or cancel event for the previous gesture // due to an app switch, ANR, or some other state change. cancelAndClearTouchTargets(ev); resetTouchState(); } // Check for interception. final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } else { // There are no touch targets and this action is not an initial down // so this view group continues to intercept touches. intercepted = true; } // If intercepted, start normal event dispatch. Also if there is already // a view that is handling the gesture, do normal event dispatch. if (intercepted || mFirstTouchTarget != null) { ev.setTargetAccessibilityFocus(false); } // Check for cancelation. final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL; // Update list of touch targets for pointer down, if needed. final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0; TouchTarget newTouchTarget = null; boolean alreadyDispatchedToNewTouchTarget = false; if (!canceled && !intercepted) { // If the event is targeting accessiiblity focus we give it to the // view that has accessibility focus and if it does not handle it // we clear the flag and dispatch the event to all children as usual. // We are looking up the accessibility focused host to avoid keeping // state since these events are very rare. View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus() ? findChildWithAccessibilityFocus() : null; if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { final int actionIndex = ev.getActionIndex(); // always 0 for down final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex) : TouchTarget.ALL_POINTER_IDS; // Clean up earlier touch targets for this pointer id in case they // have become out of sync. removePointersFromTouchTargets(idBitsToAssign); final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { final float x = ev.getX(actionIndex); final float y = ev.getY(actionIndex); // Find a child that can receive the event. // Scan children from front to back. final ArrayList1.在19~25行,是處理down事件,清除之前的狀態,cancelAndClearTouchTargets(ev)中把mFirstTouchTarget設置為空。preorderedList = buildOrderedChildList(); final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { final int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get(childIndex); // If there is a view that has accessibility focus we want it // to get the event first and if not handled we will perform a // normal dispatch. We may do a double iteration but this is // safer given the timeframe. if (childWithAccessibilityFocus != null) { if (childWithAccessibilityFocus != child) { continue; } childWithAccessibilityFocus = null; i = childrenCount - 1; } if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; } newTouchTarget = getTouchTarget(child); if (newTouchTarget != null) { // Child is already receiving touch within its bounds. // Give it the new pointer in addition to the ones it is handling. newTouchTarget.pointerIdBits |= idBitsToAssign; break; } resetCancelNextUpFlag(child); if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // Child wants to receive touch within its bounds. mLastTouchDownTime = ev.getDownTime(); if (preorderedList != null) { // childIndex points into presorted list, find original index for (int j = 0; j < childrenCount; j++) { if (children[childIndex] == mChildren[j]) { mLastTouchDownIndex = j; break; } } } else { mLastTouchDownIndex = childIndex; } mLastTouchDownX = ev.getX(); mLastTouchDownY = ev.getY(); newTouchTarget = addTouchTarget(child, idBitsToAssign); alreadyDispatchedToNewTouchTarget = true; break; } // The accessibility focus didn't handle the event, so clear // the flag and do a normal dispatch to all children. ev.setTargetAccessibilityFocus(false); } if (preorderedList != null) preorderedList.clear(); } if (newTouchTarget == null && mFirstTouchTarget != null) { // Did not find a child to receive the event. // Assign the pointer to the least recently added target. newTouchTarget = mFirstTouchTarget; while (newTouchTarget.next != null) { newTouchTarget = newTouchTarget.next; } newTouchTarget.pointerIdBits |= idBitsToAssign; } } } // Dispatch to touch targets. if (mFirstTouchTarget == null) { // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); } else { // Dispatch to touch targets, excluding the new touch target if we already // dispatched to it. Cancel touch targets if necessary. TouchTarget predecessor = null; TouchTarget target = mFirstTouchTarget; while (target != null) { final TouchTarget next = target.next; if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } if (cancelChild) { if (predecessor == null) { mFirstTouchTarget = next; } else { predecessor.next = next; } target.recycle(); target = next; continue; } } predecessor = target; target = next; } } // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { resetTouchState(); } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } } if (!handled && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1); } return handled; }
2.到28行,是判斷是否攔截事件,看看29~42這段代碼
if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } else { // There are no touch targets and this action is not an initial down // so this view group continues to intercept touches. intercepted = true; }disallowIntercept是禁止攔截
當Action_Down時,如果disallowIntercept為true,intercepted 為false,不攔截;disallowIntercept為false,執行onInterceptTouchEvent(ev)方法,返回值決定intercepted
當不是Action_Down時,如果mFirstTouchTarget ==null,intercepted 為true,攔截事件;mFirstTouchTarget !=null,執行和上面一樣。onInterceptTouchEvent(ev)默認返回時false,可以在ViewGroup裡面重寫,修改返回是否攔截。
ViewGroup中的requestDisallowInterceptTouchEvent( )方法可以用來禁止或允許ViewGroup攔截Touch事件,但是它對於ACTION_DOWN是無效的。因為在ACTION_DOWN時會調用resetTouchState()重置了FLAG_DISALLOW_INTERCEPT,所以總會調用onInterceptTouchEvent判讀是否攔截。
3.28~158,是對down事件的處理
檢查是否cancel,然後進行事件的分發。58行,事件沒有被cancel或者攔截會進入下面判斷
68~70行判斷事件是否是ACTION_DOWN,ACTION_POINTER_DOWN(多點觸控),ACTION_HOVER_MOVE(懸停),如果是執行內部的語句。
89行的for循環是查找接收touch事件的view,找到點擊位置的子view,調用dispatchTransformedTouchEvent(),把touch事件派發給子view,dispatchTransformedTouchEvent()的返回值為true,代表子view消費了事件,並且添加此子view到觸摸鏈表,放到表頭。mFirstTouchTarget 也就不為空了,否則返回false,mFirstTouchTarget 還是空。
newTouchTarget = addTouchTarget(child, idBitsToAssign);
163~197,繼續分發事件,down,move,up都會進入。注意這裡是mFirstTouchTarget不為空才進入的,也就是說view沒有處理down事件,那麼接下來的move,up事件也不會處理
當mFirstTouchTarget為空,表示ViewGroup攔截了事件,或者子view沒有消費事件,也就直接調用dispatchTransformedTouchEvent()
當mFirstTouchTarget不為空,174~175,alreadyDispatchedToNewTouchTarget為true表示已經處理了down事件
move和up事件沒有處理,調用dispatchTransformedTouchEvent()處理
下面寫個demo測試
主界面
public class MainActivity extends AppCompatActivity { private static final String TAG = "lzy"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } @Override public boolean dispatchTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "Activity-------------dispatchTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "Activity-------------dispatchTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "Activity-------------dispatchTouchEvent: ACTION_UP"); break; } return super.dispatchTouchEvent(event); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "Activity-------------onTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "Activity-------------onTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "Activity-------------onTouchEvent: ACTION_UP"); break; } return super.onTouchEvent(event); } }自定義View
public class MyView extends View { private static final String TAG = "lzy"; public MyView(Context context) { super(context); } public MyView(Context context, AttributeSet attrs) { super(context, attrs); } public MyView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } @Override public boolean dispatchTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "MyView-------------dispatchTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "MyView-------------dispatchTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "MyView-------------dispatchTouchEvent: ACTION_UP"); break; } return super.dispatchTouchEvent(event); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "MyView-------------onTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "MyView-------------onTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "MyView-------------onTouchEvent: ACTION_UP"); break; } return false; } }自定義ViewGroup
public class MyViewGroup extends ViewGroup { private static final String TAG = "lzy"; public MyViewGroup(Context context) { super(context); } public MyViewGroup(Context context, AttributeSet attrs) { super(context, attrs); } public MyViewGroup(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { setMeasuredDimension(measureSize(widthMeasureSpec), measureSize(heightMeasureSpec)); //測量每個children measureChildren(widthMeasureSpec, heightMeasureSpec); } private int measureSize(int measureSpec) { int result = 0; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); if (specMode == MeasureSpec.EXACTLY) { result = specSize; } else { result = 300; if (specMode == MeasureSpec.AT_MOST) { result = Math.min(result, specSize); } } return result; } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { MyView view = (MyView) findViewById(R.id.view); view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight()); } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "MyViewGroup-------------onInterceptTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "MyViewGroup-------------onInterceptTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "MyViewGroup-------------onInterceptTouchEvent: ACTION_UP"); break; } return super.onInterceptTouchEvent(ev); } @Override public boolean dispatchTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "MyViewGroup-------------dispatchTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "MyViewGroup-------------dispatchTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "MyViewGroup-------------dispatchTouchEvent: ACTION_UP"); break; } return super.dispatchTouchEvent(event); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Log.i(TAG, "MyViewGroup-------------onTouchEvent: ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.i(TAG, "MyViewGroup-------------onTouchEvent: ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.i(TAG, "MyViewGroup-------------onTouchEvent: ACTION_UP"); break; } return super.onTouchEvent(event); } }
1.點擊黑色區域,打印下面log,因為ViewGroup和View都沒有處理touch事件,所以只收到了down,move和up都有最外層的Activity處理
2.把View的onTouchEvent返回true,打印日志如下
3.把ViewGroup的onInterceptTouchEvent返回true,View收不到touch事件
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