Android 绘制原理浅析【干货】

//Activity
 /**
     * Set the activity content from a layout resource.  The resource will be
     * inflated, adding all top-level views to the activity.
     *
     * @param layoutResID Resource ID to be inflated.
     *
     * @see #setContentView(android.view.View)
     * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
     */
    public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }

     public Window getWindow() {
        return mWindow;
    }

//Activity
private Window mWindow;

final void attach(Context context, ActivityThread aThread,····） {
        attachBaseContext(context);
        mFragments.attachHost(null /*parent*/);
        mWindow = new PhoneWindow(this, window, activityConfigCallback);
}

//PhoneWindow
  @Override
    public void setContentView(int layoutResID) {
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
    }

//PhoneWindow
 // This is the view in which the window contents are placed. It is either
    // mDecor itself, or a child of mDecor where the contents go.
  ViewGroup mContentParent;

  private DecorView mDecor;

  private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
           mContentParent = generateLayout(mDecor);
        }
  }

  protected DecorView generateDecor(int featureId) {
        return new DecorView(context, featureId, this, getAttributes());
    }

//Activity 
 void makeVisible() {
        if (!mWindowAdded) {
            ViewManager wm = getWindowManager();
            wm.addView(mDecor, getWindow().getAttributes());
            mWindowAdded = true;
        }
        mDecor.setVisibility(View.VISIBLE);
    }

// ViewRootHandler(ViewRootImpl的内部类，用于异步消息处理，和Acitivity的启动很像)

//第一步 Handler接收W（Binder）传递来的消息
@Override
public void handleMessage(Message msg) {
    switch (msg.what) {
        case MSG_INVALIDATE:
             ((View) msg.obj).invalidate();
            break;
        case MSG_INVALIDATE_RECT:
            final View.AttachInfo.InvalidateInfo info = (View.AttachInfo.InvalidateInfo) msg.obj;
            info.target.invalidate(info.left, info.top, info.right, info.bottom);
            info.recycle();
            break;
        case MSG_DISPATCH_APP_VISIBILITY://处理Visible
            handleAppVisibility(msg.arg1 != 0);
            break;
    }    
}

void handleAppVisibility(boolean visible) {
        if (mAppVisible != visible) {
            mAppVisible = visible;
            scheduleTraversals();
            if (!mAppVisible) {
                WindowManagerGlobal.trimForeground();
            }
    }
}

 void scheduleTraversals() {
        if (!mTraversalScheduled) {
            mTraversalScheduled = true;
            mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
            //开启下次刷新，就遍历View树
            mChoreographer.postCallback(
                    Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
            if (!mUnbufferedInputDispatch) {
                scheduleConsumeBatchedInput();
            }
            notifyRendererOfFramePending();
            pokeDrawLockIfNeeded();
     }
}

 final class TraversalRunnable implements Runnable {
        @Override
        public void run() {
            doTraversal();
        }
    }
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();

 void doTraversal() {
        if (mTraversalScheduled) {
            mTraversalScheduled = false;
            mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
            performTraversals();
        }
    }    

//ViewRootImpl
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
        if (mView == null) {
            return;
        }
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
        try {
            mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }

    public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
        MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY
                && MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY;
        final boolean matchesSpecSize = getMeasuredWidth() == MeasureSpec.getSize(widthMeasureSpec)
                && getMeasuredHeight() == MeasureSpec.getSize(heightMeasureSpec);
        final boolean needsLayout = specChanged
                && (sAlwaysRemeasureExactly || !isSpecExactly || !matchesSpecSize);

          if (forceLayout || needsLayout) {
            mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;

            resolveRtlPropertiesIfNeeded();

            int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);
            if (cacheIndex < 0 || sIgnoreMeasureCache) {
            //在这里调用了onMeasure 方法
                onMeasure(widthMeasureSpec, heightMeasureSpec);
                mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
            } 
        }
    }

//ViewRootImpl
//1
 private void performDraw() {
    try {
        draw(fullRedrawNeeded);
    } finally {
        mIsDrawing = false;
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
    }
 }

 //2
  private void draw(boolean fullRedrawNeeded) {
    Surface surface = mSurface;
    if (!surface.isValid()) {
            return;
        }

     if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)) {
          return;
      }
  }

 //3
    private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
            boolean scalingRequired, Rect dirty) {

     Canvas canvas = mSurface.lockCanvas(dirty);
 }