diff --git a/es/DockData.d.ts b/es/DockData.d.ts
index d5c69f32..89b1506d 100644
--- a/es/DockData.d.ts
+++ b/es/DockData.d.ts
@@ -243,6 +243,15 @@ export interface LayoutData extends LayoutBase {
     loadedFrom?: LayoutBase;
 }
 export declare type DropDirection = 'left' | 'right' | 'bottom' | 'top' | 'middle' | 'remove' | 'before-tab' | 'after-tab' | 'float' | 'front' | 'maximize' | 'new-window' | 'move' | 'active' | 'update';
+export interface FloatSize {
+    width: number;
+    height: number;
+}
+export interface FloatPosition extends FloatSize {
+    left: number;
+    top: number;
+}
+export declare type LayoutSize = FloatSize;
 export interface DockContext {
     /** @ignore */
     getDockId(): any;
@@ -254,10 +263,7 @@ export interface DockContext {
         clientY: number;
     }, panelSize?: [number, number]): void;
     /** @ignore */
-    getLayoutSize(): {
-        width: number;
-        height: number;
-    };
+    getLayoutSize(): LayoutSize;
     /** @ignore
      * When a state change happen to the layout that's handled locally, like inside DockPanel or DockBox.
      * It still need to tell the context there is a change so DockLayout can call onLayoutChange callback.
@@ -276,12 +282,7 @@ export interface DockContext {
      *  - when direction is 'float', target doesn't matter. If this is called directly from code without any user interaction, source must be PanelData with x,y,w,h properties
      * @param floatPosition position of float panel, used only when direction="float"
      */
-    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: {
-        left: number;
-        top: number;
-        width: number;
-        height: number;
-    }): void;
+    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: FloatPosition): void;
     /**
      * Get the TabGroup defined in defaultLayout
      */
diff --git a/es/DockLayout.d.ts b/es/DockLayout.d.ts
index c9a8e328..d951ae73 100644
--- a/es/DockLayout.d.ts
+++ b/es/DockLayout.d.ts
@@ -1,5 +1,5 @@
 import * as React from "react";
-import { BoxData, DockContext, DropDirection, LayoutBase, LayoutData, PanelBase, PanelData, TabBase, TabData, TabGroup, TabPaneCache } from "./DockData";
+import { BoxData, DockContext, DropDirection, FloatPosition, LayoutBase, LayoutData, LayoutSize, PanelBase, PanelData, TabBase, TabData, TabGroup, TabPaneCache } from "./DockData";
 import * as Algorithm from "./Algorithm";
 export interface LayoutProps {
     /**
@@ -109,19 +109,11 @@ export declare class DockLayout extends DockPortalManager implements DockContext
      * @param direction @inheritDoc
      * @param floatPosition @inheritDoc
      */
-    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: {
-        left: number;
-        top: number;
-        width: number;
-        height: number;
-    }): void;
+    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: FloatPosition): void;
     /** @inheritDoc */
     find(id: string, filter?: Algorithm.Filter): PanelData | TabData | BoxData | undefined;
     /** @ignore */
-    getLayoutSize(): {
-        width: number;
-        height: number;
-    };
+    getLayoutSize(): LayoutSize;
     /** @inheritDoc */
     updateTab(id: string, newTab: TabData | null, makeActive?: boolean): boolean;
     /** @inheritDoc */
diff --git a/lib/DockData.d.ts b/lib/DockData.d.ts
index d5c69f32..89b1506d 100644
--- a/lib/DockData.d.ts
+++ b/lib/DockData.d.ts
@@ -243,6 +243,15 @@ export interface LayoutData extends LayoutBase {
     loadedFrom?: LayoutBase;
 }
 export declare type DropDirection = 'left' | 'right' | 'bottom' | 'top' | 'middle' | 'remove' | 'before-tab' | 'after-tab' | 'float' | 'front' | 'maximize' | 'new-window' | 'move' | 'active' | 'update';
+export interface FloatSize {
+    width: number;
+    height: number;
+}
+export interface FloatPosition extends FloatSize {
+    left: number;
+    top: number;
+}
+export declare type LayoutSize = FloatSize;
 export interface DockContext {
     /** @ignore */
     getDockId(): any;
@@ -254,10 +263,7 @@ export interface DockContext {
         clientY: number;
     }, panelSize?: [number, number]): void;
     /** @ignore */
-    getLayoutSize(): {
-        width: number;
-        height: number;
-    };
+    getLayoutSize(): LayoutSize;
     /** @ignore
      * When a state change happen to the layout that's handled locally, like inside DockPanel or DockBox.
      * It still need to tell the context there is a change so DockLayout can call onLayoutChange callback.
@@ -276,12 +282,7 @@ export interface DockContext {
      *  - when direction is 'float', target doesn't matter. If this is called directly from code without any user interaction, source must be PanelData with x,y,w,h properties
      * @param floatPosition position of float panel, used only when direction="float"
      */
-    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: {
-        left: number;
-        top: number;
-        width: number;
-        height: number;
-    }): void;
+    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: FloatPosition): void;
     /**
      * Get the TabGroup defined in defaultLayout
      */
diff --git a/lib/DockLayout.d.ts b/lib/DockLayout.d.ts
index c9a8e328..d951ae73 100644
--- a/lib/DockLayout.d.ts
+++ b/lib/DockLayout.d.ts
@@ -1,5 +1,5 @@
 import * as React from "react";
-import { BoxData, DockContext, DropDirection, LayoutBase, LayoutData, PanelBase, PanelData, TabBase, TabData, TabGroup, TabPaneCache } from "./DockData";
+import { BoxData, DockContext, DropDirection, FloatPosition, LayoutBase, LayoutData, LayoutSize, PanelBase, PanelData, TabBase, TabData, TabGroup, TabPaneCache } from "./DockData";
 import * as Algorithm from "./Algorithm";
 export interface LayoutProps {
     /**
@@ -109,19 +109,11 @@ export declare class DockLayout extends DockPortalManager implements DockContext
      * @param direction @inheritDoc
      * @param floatPosition @inheritDoc
      */
-    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: {
-        left: number;
-        top: number;
-        width: number;
-        height: number;
-    }): void;
+    dockMove(source: TabData | PanelData, target: string | TabData | PanelData | BoxData | null, direction: DropDirection, floatPosition?: FloatPosition): void;
     /** @inheritDoc */
     find(id: string, filter?: Algorithm.Filter): PanelData | TabData | BoxData | undefined;
     /** @ignore */
-    getLayoutSize(): {
-        width: number;
-        height: number;
-    };
+    getLayoutSize(): LayoutSize;
     /** @inheritDoc */
     updateTab(id: string, newTab: TabData | null, makeActive?: boolean): boolean;
     /** @inheritDoc */
diff --git a/src/DockData.ts b/src/DockData.ts
index 8bc0de71..b71c2015 100644
--- a/src/DockData.ts
+++ b/src/DockData.ts
@@ -310,6 +310,18 @@ export type DropDirection =
   | 'update' // tab updated with updateTab
   ;
 
+export interface FloatSize {
+  width: number;
+  height: number;
+}
+
+export interface FloatPosition extends FloatSize {
+  left: number;
+  top: number;
+}
+
+export type LayoutSize = FloatSize;
+
 export interface DockContext {
   /** @ignore */
   getDockId(): any;
@@ -321,7 +333,7 @@ export interface DockContext {
   setDropRect(element: HTMLElement, direction?: DropDirection, source?: any, event?: {clientX: number, clientY: number}, panelSize?: [number, number]): void;
 
   /** @ignore */
-  getLayoutSize(): {width: number, height: number};
+  getLayoutSize(): LayoutSize;
 
   /** @ignore
    * When a state change happen to the layout that's handled locally, like inside DockPanel or DockBox.
@@ -346,7 +358,7 @@ export interface DockContext {
     source: TabData | PanelData,
     target: string | TabData | PanelData | BoxData | null,
     direction: DropDirection,
-    floatPosition?: { left: number, top: number, width: number, height: number }
+    floatPosition?: FloatPosition
   ): void;
 
   /**
@@ -389,7 +401,7 @@ export interface DockContext {
 }
 
 /** @ignore */
-export const DockContextType = React.createContext<DockContext>(null);
+export const DockContextType = React.createContext<DockContext>(null!);
 /** @ignore */
 export const DockContextProvider = DockContextType.Provider;
 /** @ignore */
diff --git a/src/DockLayout.tsx b/src/DockLayout.tsx
index c6b7c6ef..fcaea363 100644
--- a/src/DockLayout.tsx
+++ b/src/DockLayout.tsx
@@ -7,8 +7,10 @@ import {
   DockContext,
   DockContextProvider,
   DropDirection,
+  FloatPosition,
   LayoutBase,
   LayoutData,
+  LayoutSize,
   PanelBase,
   PanelData,
   placeHolderGroup,
@@ -215,7 +217,7 @@ export class DockLayout extends DockPortalManager implements DockContext {
     source: TabData | PanelData,
     target: string | TabData | PanelData | BoxData | null,
     direction: DropDirection,
-    floatPosition?: {left: number, top: number, width: number, height: number}
+    floatPosition?: FloatPosition
   ) {
     let layout = this.getLayout();
     if (direction === 'maximize') {
@@ -280,7 +282,7 @@ export class DockLayout extends DockPortalManager implements DockContext {
   }
 
   /** @ignore */
-  getLayoutSize() {
+  getLayoutSize(): LayoutSize {
     if (this._ref) {
       return {width: this._ref.offsetWidth, height: this._ref.offsetHeight};
     }