feat: add interface for load start event

packages/core/src/LottieView/index.tsx

@@ -67,6 +67,10 @@ export class LottieView extends React.PureComponent<Props, {}> {
     Commands.resume(this.lottieAnimationViewRef);
   }
 
+  private onAnimationLoadStart = () => {
+    this.props.onAnimationLoadStart?.()
+  }
+
   private onAnimationFinish = (
     evt: NativeSyntheticEvent<{ isCancelled: boolean }>,
   ) => {
@@ -132,6 +136,7 @@ export class LottieView extends React.PureComponent<Props, {}> {
         onAnimationFinish={this.onAnimationFinish}
         onAnimationFailure={this.onAnimationFailure}
         onAnimationLoaded={this.onAnimationLoaded}
+        onAnimationLoadStarted={this.onAnimationLoadStart}
         autoPlay={autoPlay}
         resizeMode={resizeMode}
         {...sources}

packages/core/src/specs/LottieAnimationViewNativeComponent.ts

@@ -8,7 +8,9 @@ import codegenNativeComponent from 'react-native/Libraries/Utilities/codegenNati
 import codegenNativeCommands from 'react-native/Libraries/Utilities/codegenNativeCommands';
 import type { ProcessedColorValue, ViewProps, HostComponent } from 'react-native';
 
-export type OnAnimationFinishEvent = Readonly<{
+type AnimationLoadStartEvent = Readonly<{}>
+
+export type AnimationFinishEvent = Readonly<{
   isCancelled: boolean;
 }>;
 
@@ -54,8 +56,12 @@ export interface NativeProps extends ViewProps {
   dummy?: Readonly<{ dummy: boolean }>;
   textFiltersAndroid?: ReadonlyArray<TextFilterAndroidStruct>;
   textFiltersIOS?: ReadonlyArray<TextFilterIOSStruct>;
+  onAnimationLoadStart?: BubblingEventHandler<
+    AnimationLoadStartEvent,
+    'onAnimationLoadStarted'
+  >
   onAnimationFinish?: BubblingEventHandler<
-    OnAnimationFinishEvent,
+    AnimationFinishEvent,
     'onAnimationFinish'
   >;
   onAnimationFailure?: BubblingEventHandler<

packages/core/src/types.ts

@@ -107,6 +107,12 @@ export interface LottieViewProps {
    */
   autoPlay?: boolean;
 
+  /**
+   * A callback function which will be called when animation starts loading.
+   * @platform ios, android, web
+   */
+  onAnimationLoadStart?: () => void
+
   /**
    * A callback function which will be called when animation is finished. Note that this
    * callback will be called only when `loop` is set to false.