Save Scrollviews Position and Scroll Back to It Later (Offset to Position)

Save ScrollViews position and scroll back to it later (offset to position)

You don't need actually offset in this scenario, just store id of currently visible view (you can use any appropriate algorithm for your data of how to detect it) and then scroll to view with that id.

Here is a simplified demo of possible approach. Tested with Xcode 12.1/iOS 14.1

struct TestScrollBackView: View {
    @State private var stored: Int = 0
    @State private var current: [Int] = []
    
    var body: some View {
        ScrollViewReader { proxy in
            VStack {
                HStack {
                    Button("Store") {
                        // hard code is just for demo !!!
                        stored = current.sorted()[1] // 1st is out of screen by LazyVStack
                        print("!! stored \(stored)")
                    }
                    Button("Restore") {
                        proxy.scrollTo(stored, anchor: .top)
                        print("[x] restored \(stored)")
                    }
                }
                Divider()
                ScrollView {
                    LazyVStack {
                        ForEach(0..<1000, id: \.self) { obj in
                            Text("Item: \(obj)")
                                .onAppear {
                                    print(">> added \(obj)")
                                    current.append(obj)
                                }
                                .onDisappear {
                                    current.removeAll { $0 == obj }
                                    print("<< removed \(obj)")
                                }.id(obj)
                        }
                    }
                }
            }
        }
    }
}

Get the current scroll position of a SwiftUI ScrollView

It was possible to read it and before. Here is a solution based on view preferences.

struct DemoScrollViewOffsetView: View {
    @State private var offset = CGFloat.zero
    var body: some View {
        ScrollView {
            VStack {
                ForEach(0..<100) { i in
                    Text("Item \(i)").padding()
                }
            }.background(GeometryReader {
                Color.clear.preference(key: ViewOffsetKey.self,
                    value: -$0.frame(in: .named("scroll")).origin.y)
            })
            .onPreferenceChange(ViewOffsetKey.self) { print("offset >> \($0)") }
        }.coordinateSpace(name: "scroll")
    }
}

struct ViewOffsetKey: PreferenceKey {
    typealias Value = CGFloat
    static var defaultValue = CGFloat.zero
    static func reduce(value: inout Value, nextValue: () -> Value) {
        value += nextValue()
    }
}

Best Way: Save & Restore TextView Position in ScrollView

I am so proud to say, I got a perfect solution to this now.

Sh.... (sorry I am too excited about it. If you find any mistakes/bugs/weakness on it, please DO give me your valuable suggestions and please feel free to correct me. :-)

Cut the crap. Here you go !!!

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    final ScrollView scrollView = (ScrollView) findViewById(R.id.Trial_C_ScrollViewContainer);
    final TextView textView = (TextView) scrollView.getChildAt(0);
    final int firstVisableLineOffset = textView.getLayout().getLineForVertical(scrollView.getScrollY());
    final int firstVisableCharacterOffset = textView.getLayout().getLineStart(firstVisableLineOffset);
    outState.putInt(ScrollViewContainerTextViewFirstVisibleCharacterOffset, firstVisableCharacterOffset);
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    final int firstVisableCharacterOffset = savedInstanceState.getInt(ScrollViewContainerTextViewFirstVisibleCharacterOffset);

    final ScrollView scrollView = (ScrollView) findViewById(R.id.Trial_C_ScrollViewContainer);
    scrollView.post(new Runnable() {
        public void run() {
            final TextView textView = (TextView) scrollView.getChildAt(0);
            final int firstVisableLineOffset = textView.getLayout().getLineForOffset(firstVisableCharacterOffset);
            final int pixelOffset = textView.getLayout().getLineTop(firstVisableLineOffset);
            scrollView.scrollTo(0, pixelOffset);
        }
    });
}

That's it. :-)

If it helps you, please clap your hands. <-- this is important!!

And if you wish to, click that little upright triangle. (make sure you have clapped your hands first!)

How to save RecyclerView's scroll position using RecyclerView.State?

How do you plan to save last saved position with RecyclerView.State?

You can always rely on ol' good save state. Extend RecyclerView and override onSaveInstanceState() and onRestoreInstanceState():

    @Override
    protected Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        LayoutManager layoutManager = getLayoutManager();
        if(layoutManager != null && layoutManager instanceof LinearLayoutManager){
            mScrollPosition = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
        }
        SavedState newState = new SavedState(superState);
        newState.mScrollPosition = mScrollPosition;
        return newState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        super.onRestoreInstanceState(state);
        if(state != null && state instanceof SavedState){
            mScrollPosition = ((SavedState) state).mScrollPosition;
            LayoutManager layoutManager = getLayoutManager();
            if(layoutManager != null){
              int count = layoutManager.getItemCount();
              if(mScrollPosition != RecyclerView.NO_POSITION && mScrollPosition < count){
                  layoutManager.scrollToPosition(mScrollPosition);
              }
            }
        }
    }

    static class SavedState extends android.view.View.BaseSavedState {
        public int mScrollPosition;
        SavedState(Parcel in) {
            super(in);
            mScrollPosition = in.readInt();
        }
        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(mScrollPosition);
        }
        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            @Override
            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

ScrollView doesn't keep track of current position. When tapped it resets back to previous location

Its may be the problem with props in the Model which is related to scroll.

as you use ScrollView inside the Model, assuming that , you need a dismissable scrollview

Please checkout a sample related to that : https://gist.github.com/mmitchellgarcia/6ee4d5b5c79162e3cc13b67d743777e6#file-dismissablescrollview-js

For more : https://github.com/react-native-community/react-native-modal/issues/109

Hope it helps

How to keep scroll position after state update in React Native ScrollView

create a ref variable

const ScrollViewRef = useRef();

then in ScrollView write like this

<ScrollView
  ref={ScrollViewRef}
  // onLayout will make sure it scroll to Bottom initially
  onLayout={() => ScrollViewRef.current.scrollToEnd()}

  // We don't need `onContentSizeChanged`
  // this onScroll fetches data  when scroll reaches top
  // then it scrolls to last position as you asked

  onScroll={({ nativeEvent }) => {
    if (ifCloseToTop(nativeEvent)) {
      handleLoadMore()
      ScrollViewRef.current.scrollTo({
        y: nativeEvent.layoutMeasurement.height,
        x: 0,
        animated: false,
      });
    }
  }}
  scrollEventThrottle={400}>
      <View style={styles.head}>
         // messages
      </View>
</ScrollView>

Don't forget to import useRef at the top

import {useRef} from "react-native";

Working Example here

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