private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff, boolean scalingRequired, Rect dirty) { Canvas canvas; try { final int left = dirty.left; final int top = dirty.top; final int right = dirty.right; final int bottom = dirty.bottom; 　　//获取一块画布，这块画布会传递到各个onDraw方法中 canvas = mSurface.lockCanvas(dirty); // The dirty rectangle can be modified by Surface.lockCanvas() (left != dirty.left || top != dirty.top || right != dirty.right || bottom != dirty.bottom) { attachInfo.mIgnoreDirtyState = true; } // TODO: Do this in native canvas.setDensity(mDensity); } catch (Surface.OutOfResourcesException e) { handleOutOfResourcesException(e); return false; } catch (IllegalArgumentException e) { Log.e(TAG, "Could not lock surface", e); // Don‘t assume this is due to out of memory, it could be // something else, and if it is something else then we could // kill stuff (or ourself) for no reason. mLayoutRequested = ; } try { if (DEBUG_ORIENTATION || DEBUG_DRAW) { Log.v(TAG, "Surface " + surface + " drawing to bitmap w=" + canvas.getWidth() + ", h=" + canvas.getHeight()); //canvas.drawARGB(255, 255, 0, 0); } // If this bitmap‘s format includes an alpha channel, we // need to clear it before drawing so that the child will // properly re-composite its drawing on a transparent // background. This automatically respects the clip/dirty region // or // If we are applying an offset, we need to clear the area // where the offset doesn‘t appear to avoid having garbage (!canvas.isOpaque() || yoff != 0 || xoff != 0) { canvas.drawColor(0, PorterDuff.Mode.CLEAR); } dirty.setEmpty(); mIsAnimating = false; mView.mPrivateFlags |= View.PFLAG_DRAWN; if (DEBUG_DRAW) { Context cxt = mView.getContext(); Log.i(TAG, "Drawing: package:" + cxt.getPackageName() + ", metrics=" + cxt.getResources().getDisplayMetrics() + ", compatibilityInfo=" + cxt.getResources().getCompatibilityInfo()); } try { canvas.translate(-xoff, -yoff); if (mTranslator != null) { mTranslator.translateCanvas(canvas); } canvas.setScreenDensity(scalingRequired ? mNoncompatDensity : 0); attachInfo.mSetIgnoreDirtyState = false; 　　　　//从这开始触发整个view树的绘制 mView.draw(canvas); drawAccessibilityFocusedDrawableIfNeeded(canvas); } finally { if (!attachInfo.mSetIgnoreDirtyState) { // Only clear the flag if it was not set during the mView.draw() call attachInfo.mIgnoreDirtyState = false; } } } finally { try { surface.unlockCanvasAndPost(canvas); } catch (IllegalArgumentException e) { Log.e(TAG, "Could not unlock surface", e); mLayoutRequested = true; // ask wm for a new surface next time. ; } if (LOCAL_LOGV) { Log.v(TAG, "Surface " + surface + " unlockCanvasAndPost"); } } return true; }

 这个方法的作用就是先从系统的Surface中获取一块画布，设置好画布的属性后传递到DecorView的draw方法中，从而激活整个view的绘画流程