在Android系统中，一个Activity的Window创建和添加过程

public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    if (view == null) {
        throw new IllegalArgumentException("view must not be null");
    }
    if (display == null) {
        throw new IllegalArgumentException("display must not be null");
    }
    if (!(params instanceof WindowManager.LayoutParams)) {
        throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
    }
    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    if (parentWindow != null) {
        parentWindow.adjustLayoutParamsForSubWindow(wparams);
    } else {
        final Context context = view.getContext();
        if (context != null
                && (context.getApplicationInfo().flags
                        & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
            wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
        }
    }
    ViewRootImpl root;
    View panelParentView = null;
    ...
        int index = findViewLocked(view, false);
        if (index >= 0) {
            if (mDyingViews.contains(view)) {
                // Don't wait for MSG_DIE to make it's way through root's queue.
                mRoots.get(index).doDie();
            } else {
                throw new IllegalStateException("View " + view
                        + " has already been added to the window manager.");
            }
            // The previous removeView() had not completed executing. Now it has.
        }
        if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
            final int count = mViews.size();
            for (int i = 0; i < count; i++) {
                if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                    panelParentView = mViews.get(i);
                }
            }
        }
        root = new ViewRootImpl(view.getContext(), display);
        view.setLayoutParams(wparams);
        mViews.add(view);
        mRoots.add(root);
        mParams.add(wparams);
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            if (index >= 0) {
                removeViewLocked(index, true);
            }
            throw e;
        }
    }
}

WindowManagerGlobal的addView法子重要实现三个步调：

• 搜查参数能否正当，要是是子Window借需求调零一些组织参数
• 建立ViewRootImpl，并将传出去的View加添到mViews列内外
• 经由过程ViewRootImpl来更新界里并实现Window的加添历程。

终极挪用了root.setView(view, wparams, panelParentView)法子。

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    ...
    requestLayout();
    ...
    try {
    mOrigWindowType = mWindowAttributes.type;
    mAttachInfo.mRecomputeGlobalAttributes = true;
    collectViewAttributes();
    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
            getHostVisibility(), mDisplay.getDisplayId(),
            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
            mAttachInfo.mOutsets, mInputChannel);
    ...
}

@Override
public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
        int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,
        Rect outOutsets, InputChannel outInputChannel) {
    return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
            outContentInsets, outStableInsets, outOutsets, outInputChannel);
}