preface
We have talked about layout measurement, now let’s see, how does it accomplish layout
View Layout
After the performTraversals measurement is called, we go back and we see the performLayout call, and then our specific layout is placed from here. So what do we need to know about her specific layout
.final booleandidLayout = layoutRequested && (! mStopped || mReportNextDraw);boolean triggerGlobalLayoutListener = didLayout
|| mAttachInfo.mRecomputeGlobalAttributes;
if (didLayout) {
performLayout(lp, mWidth, mHeight);
// By this point all views have been sized and positioned
// We can compute the transparent area
if((host.mPrivateFlags & View.PFLAG_REQUEST_TRANSPARENT_REGIONS) ! =0) {
// start out transparent
// TODO: AVOID THAT CALL BY CACHING THE RESULT?
host.getLocationInWindow(mTmpLocation);
mTransparentRegion.set(mTmpLocation[0], mTmpLocation[1],
mTmpLocation[0] + host.mRight - host.mLeft,
mTmpLocation[1] + host.mBottom - host.mTop);
host.gatherTransparentRegion(mTransparentRegion);
if(mTranslator ! =null) {
mTranslator.translateRegionInWindowToScreen(mTransparentRegion);
}
if(! mTransparentRegion.equals(mPreviousTransparentRegion)) { mPreviousTransparentRegion.set(mTransparentRegion); mFullRedrawNeeded =true;
// reconfigure window manager
try {
mWindowSession.setTransparentRegion(mWindow, mTransparentRegion);
} catch (RemoteException e) {
}
}
}
if (DBG) {
System.out.println("= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =");
System.out.println("performTraversals -- after setFrame"); host.debug(); }}...Copy the codePerformLayout ()
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
int desiredWindowHeight) {
mLayoutRequested = false;
mScrollMayChange = true;
mInLayout = true;
final View host = mView;
if (host == null) {
return;
}
if (DEBUG_ORIENTATION || DEBUG_LAYOUT) {
Log.v(mTag, "Laying out " + host + " to (" +
host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout");
try {
host.layout(0.0, host.getMeasuredWidth(), host.getMeasuredHeight());
mInLayout = false;
int numViewsRequestingLayout = mLayoutRequesters.size();
if (numViewsRequestingLayout > 0) {
// requestLayout() was called during layout.
// If no layout-request flags are set on the requesting views, there is no problem.
// If some requests are still pending, then we need to clear those flags and do
// a full request/measure/layout pass to handle this situation.
ArrayList<View> validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters,
false);
if(validLayoutRequesters ! =null) {
// Set this flag to indicate that any further requests are happening during
// the second pass, which may result in posting those requests to the next
// frame instead
mHandlingLayoutInLayoutRequest = true;
// Process fresh layout requests, then measure and layout
int numValidRequests = validLayoutRequesters.size();
for (int i = 0; i < numValidRequests; ++i) {
final View view = validLayoutRequesters.get(i);
Log.w("View"."requestLayout() improperly called by " + view +
" during layout: running second layout pass");
view.requestLayout();
}
measureHierarchy(host, lp, mView.getContext().getResources(),
desiredWindowWidth, desiredWindowHeight);
mInLayout = true;
host.layout(0.0, host.getMeasuredWidth(), host.getMeasuredHeight());
mHandlingLayoutInLayoutRequest = false;
// Check the valid requests again, this time without checking/clearing the
// layout flags, since requests happening during the second pass get noop'd
validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true);
if(validLayoutRequesters ! =null) {
final ArrayList<View> finalRequesters = validLayoutRequesters;
// Post second-pass requests to the next frame
getRunQueue().post(new Runnable() {
@Override
public void run(a) {
int numValidRequests = finalRequesters.size();
for (int i = 0; i < numValidRequests; ++i) {
final View view = finalRequesters.get(i);
Log.w("View"."requestLayout() improperly called by " + view +
" during second layout pass: posting in next frame"); view.requestLayout(); }}}); }}}}finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
mInLayout = false;
}
Copy the codeHere we can observe that host is the DectorView, and down here we call host.layout. I’m going to pass in the starting point x=0,y=0, and I’m going to pass in the measured width and height
public void layout(int l, int t, int r, int b) {
// If it is not the first time, skip it or it will be measured here
if((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) ! =0) {
onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
}
// Initialize the left, right, and upper points for the first time
int oldL = mLeft;
int oldT = mTop;
int oldB = mBottom;
int oldR = mRight;
/ / initialized here call setFrame mLeft, mRight, mTop, mBottom these four values
boolean changed = isLayoutModeOptical(mParent) ?
setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
onLayout(changed, l, t, r, b);
if (shouldDrawRoundScrollbar()) {
if(mRoundScrollbarRenderer == null) {
mRoundScrollbarRenderer = new RoundScrollbarRenderer(this); }}else {
mRoundScrollbarRenderer = null;
}
mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
ListenerInfo li = mListenerInfo;
if(li ! =null&& li.mOnLayoutChangeListeners ! =null) {
ArrayList<OnLayoutChangeListener> listenersCopy =
(ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
int numListeners = listenersCopy.size();
for (int i = 0; i < numListeners; ++i) {
listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
}
}
}
mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
if((mPrivateFlags3 & PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT) ! =0) {
mPrivateFlags3 &= ~PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT;
notifyEnterOrExitForAutoFillIfNeeded(true); }}Copy the codeAbove we can see that one of the main things we do with our layout is initialize our top, bottom, left, and right points with setFrame().
protected boolean setFrame(int left, int top, int right, int bottom) { boolean changed = false; if (DBG) { Log.d("View", this + " View.setFrame(" + left + "," + top + "," + right + "," + bottom + ")"); } if (mLeft ! = left || mRight ! = right || mTop ! = top || mBottom ! = bottom) { changed = true; // Remember our drawn bit int drawn = mPrivateFlags & PFLAG_DRAWN; int oldWidth = mRight - mLeft; int oldHeight = mBottom - mTop; int newWidth = right - left; int newHeight = bottom - top; boolean sizeChanged = (newWidth ! = oldWidth) || (newHeight ! = oldHeight); // Invalidate our old position (Invalidate our old information) Invalidate (sizeChanged); MLeft = left; mTop = top; mRight = right; mBottom = bottom; mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom); mPrivateFlags |= PFLAG_HAS_BOUNDS;Copy the code if (sizeChanged) {
sizeChange(newWidth, newHeight, oldWidth, oldHeight);
}
if((mViewFlags & VISIBILITY_MASK) == VISIBLE || mGhostView ! =null) {
// If we are visible, force the DRAWN bit to on so that
// this invalidate will go through (at least to our parent).
// This is because someone may have invalidated this view
// before this call to setFrame came in, thereby clearing
// the DRAWN bit.
mPrivateFlags |= PFLAG_DRAWN;
invalidate(sizeChanged);
// parent display list may need to be recreated based on a change in the bounds
// of any child
invalidateParentCaches();
}
// Reset drawn bit to original value (invalidate turns it off)
mPrivateFlags |= drawn;
mBackgroundSizeChanged = true;
mDefaultFocusHighlightSizeChanged = true;
if(mForegroundInfo ! =null) {
mForegroundInfo.mBoundsChanged = true;
}
notifySubtreeAccessibilityStateChangedIfNeeded();
}
return changed;
}
Copy the codeDuring initialization, setFrame will compare whether it is the same as the previous one. If so, it will not proceed here. If so, our old information will be invalidate(sizeChanged) directly. So the layout is almost complete, but we don’t see the child View of DectorView layout, and we remember that we called the onLayout of the current DectorView, that is, the onLayout of the View
/** * Called from layout when this view should * assign a size and position to each of its children. * * Derived classes with children should override * this method and call layout on each of * their children. *@param changed This is a new size or position for this view
* @param left Left position, relative to parent
* @param top Top position, relative to parent
* @param right Right position, relative to parent
* @param bottom Bottom position, relative to parent
*/
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {}Copy the codeSo I saw an empty piece of code, and I didn’t know why, but then I remembered that the prototype for host in this class right now is a View, and when we’re actually using it, it’s a DectorView and I found it
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom); . }Copy the codeHe’s calling his dad’s onLayout and her dad’s FreamLayout so find the final destination
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
layoutChildren(left, top, right, bottom, false /* no force left gravity */);
}
Copy the codeNotice here, one of the core things to notice here is that as with the measurement process we talked about before, my layout is the same, each component of the layout is implemented differently and in this case we’re using FreamLayout, where it starts calling a layoutChildren()
void layoutChildren(int left, int top, int right, int bottom, boolean forceLeftGravity) {
final int count = getChildCount();
final int parentLeft = getPaddingLeftWithForeground();
final int parentRight = right - left - getPaddingRightWithForeground();
final int parentTop = getPaddingTopWithForeground();
final int parentBottom = bottom - top - getPaddingBottomWithForeground();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if(child.getVisibility() ! = GONE) {final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final int width = child.getMeasuredWidth();
final int height = child.getMeasuredHeight();
int childLeft;
int childTop;
int gravity = lp.gravity;
if (gravity == -1) {
gravity = DEFAULT_CHILD_GRAVITY;
}
final int layoutDirection = getLayoutDirection();
final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
final int verticalGravity = gravity & Gravity.VERTICAL_GRAVITY_MASK;
switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
case Gravity.CENTER_HORIZONTAL:
childLeft = parentLeft + (parentRight - parentLeft - width) / 2 +
lp.leftMargin - lp.rightMargin;
break;
case Gravity.RIGHT:
if(! forceLeftGravity) { childLeft = parentRight - width - lp.rightMargin;break;
}
case Gravity.LEFT:
default:
childLeft = parentLeft + lp.leftMargin;
}
switch (verticalGravity) {
case Gravity.TOP:
childTop = parentTop + lp.topMargin;
break;
case Gravity.CENTER_VERTICAL:
childTop = parentTop + (parentBottom - parentTop - height) / 2 +
lp.topMargin - lp.bottomMargin;
break;
case Gravity.BOTTOM:
childTop = parentBottom - height - lp.bottomMargin;
break;
default: childTop = parentTop + lp.topMargin; } child.layout(childLeft, childTop, childLeft + width, childTop + height); }}}Copy the codeAt this time, we will find that our component is iterating through the current child view, and then they will call their own layout method to position. Therefore, we can see that the layout process is actually the top layer, and the top layer will start layout to position the layout. And then onLayout calls the child view and lets the child view call its own layout and position itself for all the purposes of positioning itself,
Conclusion:
So in fact, as long as we are clear about the current drawing process and layout process, we need to develop our own custom layout in fact, we only need to add our own business code, whether FreamLayout, or LinearLayout and other official layout components, are in accordance with this mechanism to play, It’s just adding their business to achieve the corresponding effect.
So, at this point, the drawing process is OK! Ok, so far, this article I will introduce the end ~ welcome to pay attention to my public number [small new chat Android], here I hope you can harvest more knowledge, we see you next issue!