//我在Fragment中创建了RecycleView，如下所示：
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_new_shop, container, false);
recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
stackView = (RelativeLayout) view.findViewById(R.id.stack_view);
firstStack = (CustomImageView) view.findViewById(R.id.firstStack);
secondStack = (CustomImageView) view.findViewById(R.id.secondStack);
thirdStack = (CustomImageView) view.findViewById(R.id.thirdStack);
stackTopGap = view.findViewById(R.id.view);
new Handler().post(new Runnable() {
@Override
public void run() {
firstStack.getLayoutParams().width = stackView.getWidth() - 40;
secondStack.getLayoutParams().width = stackView.getWidth() - 80;
thirdStack.getLayoutParams().width = stackView.getWidth() - 120;
width = thirdStack.getLayoutParams().width;
recyclerView.getLayoutParams().height = recyclerView.getHeight() - (firstStack.getHeight() + stackTopGap.getHeight());
stackView.getLayoutParams().height = firstStack.getHeight();
}
});
recyclerView.setHasFixedSize(true);
linearLayoutManager=new LinearLayoutManager(getActivity()) {
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
// A good idea would be to create this instance in some initialization method, and just set the target position in this method.
LinearSmoothScroller smoothScroller = new LinearSmoothScroller(getContext()) {
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
//int yDelta = calculateCurrentDistanceToPosition(targetPosition);
return new PointF(0, 200);
}
// This is the important method. This code will return the amount of time it takes to scroll 1 pixel.
// This code will request X milliseconds for every Y DP units.
@Override
protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
return 7 / TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 7, displayMetrics);
}
};
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
};
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
@Override
public void onScrolled(final RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
final int positionView = ((LinearLayoutManager) recyclerView.getLayoutManager()).findLastVisibleItemPosition();
if (dy > 0) {
if (positionView >= 2) {
final View view = recyclerView.getChildAt(2);
if (view != null && recyclerView.getChildAdapterPosition(view) == positionView) {
TranslateAnimation translateAnimation = new TranslateAnimation(0, 0, 200, 0);
translateAnimation.setAnimationListener(new Animation.AnimationListener() {
@Override
public void onAnimationStart(Animation animation) {
if (counter == 0) {
if (recyclerView.getAdapter().getItemCount() - 4 >= positionView) {
createStackImageView();
}
if (stackView.getChildAt(1) != null) {
//stackView.getChildAt(1).setScaleX(1.5f);
}
counter++;
}
recyclerView.smoothScrollToPosition(positionView);
}
@Override
public void onAnimationEnd(Animation animation) {
view.clearAnimation();
stackView.requestLayout();
stackView.removeView(stackView.getChildAt(1));
stackView.invalidate();
try {
for (int i = 1; i < 4; i++) {
Glide.with(getActivity())
.load(JSONUrl.IMAGE_BASE_URL + imageList.get(positionView + i))
.into((ImageView) stackView.getChildAt(i));
}
} catch (IndexOutOfBoundsException | NullPointerException | IllegalArgumentException ex) {
ex.printStackTrace();
}
counter = 0;
}
@Override
public void onAnimationRepeat(Animation animation) {
}
});
translateAnimation.setDuration(150);
view.setAnimation(translateAnimation);
}
}
for (int i = stackView.getChildCount() - 1; i >= 2; i--) {
ResizeAnimation resizeAnimation = new ResizeAnimation(stackView.getChildAt(i));
resizeAnimation.setHeights(stackView.getChildAt(i).getHeight(), stackView.getChildAt(i - 1).getHeight());
resizeAnimation.setWidths(stackView.getChildAt(i).getWidth(), stackView.getChildAt(i - 1).getWidth());
resizeAnimation.setDuration(200);
stackView.getChildAt(i).startAnimation(resizeAnimation);
}
} else if (dy < 0) {
final int position = ((LinearLayoutManager) recyclerView.getLayoutManager()).findLastVisibleItemPosition();
if (position == imageList.size() - 1) {
stackView.removeView(firstStack);
stackView.addView(firstStack);
stackView.invalidate();
stackView.requestLayout();
stackView.getChildAt(1).setVisibility(View.VISIBLE);
Glide.with(getActivity())
.load(JSONUrl.IMAGE_BASE_URL + imageList.get(imageList.size() - 1))
.into((ImageView) stackView.getChildAt(1));
} else if (position == imageList.size() - 2) {
stackView.removeView(secondStack);
stackView.addView(secondStack);
secondStack.getLayoutParams().height = firstStack.getHeight() - 20;
secondStack.getLayoutParams().width = firstStack.getWidth() - 40;
stackView.invalidate();
stackView.requestLayout();
stackView.getChildAt(2).setVisibility(View.VISIBLE);
Glide.with(getActivity())
.load(JSONUrl.IMAGE_BASE_URL + imageList.get(imageList.size() - 2))
.into((ImageView) stackView.getChildAt(2));
} else if (position == imageList.size() - 3) {
stackView.removeView(thirdStack);
stackView.addView(thirdStack);
thirdStack.getLayoutParams().height = secondStack.getHeight() - 20;
thirdStack.getLayoutParams().width = secondStack.getWidth() - 40;
stackView.invalidate();
stackView.requestLayout();
stackView.getChildAt(3).setVisibility(View.VISIBLE);
Glide.with(getActivity())
.load(JSONUrl.IMAGE_BASE_URL + imageList.get(imageList.size() - 3))
.into((ImageView) stackView.getChildAt(3));
} else {
stackView.removeView(firstStack);
stackView.addView(firstStack);
stackView.invalidate();
stackView.requestLayout();
}
}
}
});
return view;
}
//在validateToken方法中，数据取自json，并设置为适配器，如下所示。
private void validateToken() {
final SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
if (new ConnectionManager(getActivity()).isConnectedToInternet()) {
final SweetAlertDialog pDialog = new AlertDIalogMessage().showProgressDialog(getActivity(), "Loading...");
if (sharedPreferences.getString(SharedPrefrenceInfo.IS_TOKEN_VALID, "token_invalid").equals("token_invalid")) {
Utils.setTokenInfo(getActivity(), pDialog, new AccessTokenInfoHolder() {
@Override
public void setAcessTokenInfo(String accessToken, String expires_in, String token_type) {
Log.e("Access Token", accessToken);
new ShopFragmentJson(getActivity()).getShopPageContent(pDialog, sharedPreferences.getString(SharedPrefrenceInfo.TOKEN_TYPE, "") + " " + sharedPreferences.getString(SharedPrefrenceInfo.IS_TOKEN_VALID, ""), new ShopPageContentHolder() {
@Override
public void setErrorShopPageContent(String statusCode, String statusText) {
//do nothing here since the case unauthorized will not arrive for the first time
}
@Override
public void setSuccessShopPageContent(String success, String data) {
if (success.equals("true")) {
shoppageInfoList = getShopPageContent(data);
//set the adapter after loading data from url
final NewShopFragmentAdapter recyclerViewAdapter = new NewShopFragmentAdapter(getActivity(), recyclerView.getHeight(), shoppageInfoList);
recyclerView.setAdapter(recyclerViewAdapter);
pDialog.dismiss();
} else {
pDialog.dismiss();
new AlertDIalogMessage().showErrorDialog(getActivity(), data);
}
}
});
}
});
} else {
new ShopFragmentJson(getActivity()).getShopPageContent(pDialog, sharedPreferences.getString(SharedPrefrenceInfo.TOKEN_TYPE, "") + " " + sharedPreferences.getString(SharedPrefrenceInfo.IS_TOKEN_VALID, ""), new ShopPageContentHolder() {
@Override
public void setErrorShopPageContent(String statusCode, String statusText) {
//this method is invoked when unauthorized response come from server
Utils.setTokenInfo(getActivity(), pDialog, new AccessTokenInfoHolder() {
@Override
public void setAcessTokenInfo(String accessToken, String expires_in, String token_type) {
new ShopFragmentJson(getActivity()).getShopPageContent(pDialog, sharedPreferences.getString(SharedPrefrenceInfo.TOKEN_TYPE, "") + " " + sharedPreferences.getString(SharedPrefrenceInfo.IS_TOKEN_VALID, ""), new ShopPageContentHolder() {
@Override
public void setErrorShopPageContent(String statusCode, String statusText) {
//do nothing here since the case unauthorized will not arrive for the first time
}
@Override
public void setSuccessShopPageContent(String success, String data) {
if (success.equals("true")) {
List<ShoppageInfo> shoppageInfoList = getShopPageContent(data);
final NewShopFragmentAdapter recyclerViewAdapter = new NewShopFragmentAdapter(getActivity(), recyclerView.getHeight(), shoppageInfoList);
recyclerView.setAdapter(recyclerViewAdapter);
pDialog.dismiss();
} else {
pDialog.dismiss();
new AlertDIalogMessage().showErrorDialog(getActivity(), data);
}
}
});
}
});
}
@Override
public void setSuccessShopPageContent(String success, String data) {
if (success.equals("true")) {
List<ShoppageInfo> shoppageInfoList = getShopPageContent(data);
//set the adapter after loading data from url
final NewShopFragmentAdapter recyclerViewAdapter = new NewShopFragmentAdapter(getActivity(), recyclerView.getHeight(), shoppageInfoList);
recyclerView.setAdapter(recyclerViewAdapter);
pDialog.dismiss();
} else {
pDialog.dismiss();
new AlertDIalogMessage().showErrorDialog(getActivity(), data);
}
}
});
}
} else {
new SweetAlertDialog(getActivity(), SweetAlertDialog.ERROR_TYPE)
.setTitleText("Oops...")
.setContentText("No internet connection!")
.show();
}
}
在onResume方法中没有，我调用验证令牌如下：
@Override
public void onResume() {
super.onResume();
validateToken();
}
//现在，当我从这个片段中调用一些活动并返回时，会调用validate方法，并重新加载RecyclerView适配器。现在，我想要的是保持RecyclerView的状态，这样当我从活动返回时，RecyclerView将保持在调用活动时的滚动位置。但对我来说，问题是它总是从一开始就存在。我也看到一些Stack Overflow的帖子，他们建议我使用Parceable，但我没有得到任何好处。Is什么都不做。
可以试试这个。您需要为每一行维护一个标识符。然后在转到活动之前保存第一个可见行的标识符。然后，当您返回时，再次选择该特定行。