Added onSnapReached prop which runs a given callback passing to it th…

…e index of the running snappingPoint and it's height.

SlidingUpPanel.js

@@ -80,6 +80,7 @@ class SlidingUpPanel extends React.PureComponent {
     backdropOpacity: 0.75,
     friction: Constants.DEFAULT_FRICTION,
     onBottomReached: () => null,
+    onSnapReached: () => null,
   }
 
   // eslint-disable-next-line react/sort-comp
@@ -282,11 +283,16 @@ class SlidingUpPanel extends React.PureComponent {
 
   _onAnimatedValueChange({value}) {
     const isAtBottom = this._isAtBottom(value)
+    const isAtSnap = this._isAtSnap(value)
 
     if (isAtBottom) {
       this.props.onBottomReached()
       this.props.avoidKeyboard && Keyboard.dismiss()
     }
+    if (isAtSnap > -1 && !isAtBottom) {
+      this.props.onSnapReached(isAtSnap, value);
+      this.props.avoidKeyboard && Keyboard.dismiss()
+    }
 
     if (this._backdrop == null) {
       return
@@ -369,6 +375,15 @@ class SlidingUpPanel extends React.PureComponent {
     return value <= bottom
   }
 
+  _isAtSnap(value) {
+    const snappingPoints= this.props.snappingPoints;
+    let found = -1;
+    if (snappingPoints) {
+      found = snappingPoints.findIndex((point) => point === value);
+    }
+    return found;
+  }
+
   _storeKeyboardPosition(value) {
     this._keyboardYPosition = value
   }