Fixed the app crashes that occurred when deleting letters in a search.

core/src/main/java/org/kiwix/kiwixmobile/core/search/SearchFragment.kt

@@ -43,7 +43,10 @@ import androidx.recyclerview.widget.RecyclerView
 import io.reactivex.android.schedulers.AndroidSchedulers
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.cancelAndJoin
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
 import org.kiwix.kiwixmobile.core.R
 import org.kiwix.kiwixmobile.core.base.BaseActivity
@@ -86,6 +89,7 @@ class SearchFragment : BaseFragment() {
   private var searchAdapter: SearchAdapter? = null
   private var isDataLoading = false
   private var renderingJob: Job? = null
+  private val searchMutex = Mutex()
 
   override fun inject(baseActivity: BaseActivity) {
     baseActivity.cachedComponent.inject(this)
@@ -252,22 +256,25 @@ class SearchFragment : BaseFragment() {
     )
   }
 
-  private fun render(state: SearchState) {
-    renderingJob?.cancel()
-    isDataLoading = false
-    searchInTextMenuItem?.isVisible = state.searchOrigin == FromWebView
-    searchInTextMenuItem?.isEnabled = state.searchTerm.isNotBlank()
-    fragmentSearchBinding?.searchLoadingIndicator?.isShowing(true)
-    renderingJob = searchViewModel.viewModelScope.launch(Dispatchers.Main) {
-      val searchResult = withContext(Dispatchers.IO) {
-        state.getVisibleResults(0)
-      }
+  private suspend fun render(state: SearchState) {
+    searchMutex.withLock {
+      // `cancelAndJoin` cancels the previous running job and waits for it to completely cancel.
+      renderingJob?.cancelAndJoin()
+      isDataLoading = false
+      searchInTextMenuItem?.isVisible = state.searchOrigin == FromWebView
+      searchInTextMenuItem?.isEnabled = state.searchTerm.isNotBlank()
+      fragmentSearchBinding?.searchLoadingIndicator?.isShowing(true)
+      renderingJob = searchViewModel.viewModelScope.launch(Dispatchers.Main) {
+        val searchResult = withContext(Dispatchers.IO) {
+          state.getVisibleResults(0, renderingJob)
+        }
 
-      fragmentSearchBinding?.searchLoadingIndicator?.isShowing(false)
+        fragmentSearchBinding?.searchLoadingIndicator?.isShowing(false)
 
-      searchResult?.let {
-        fragmentSearchBinding?.searchNoResults?.isVisible = it.isEmpty()
-        searchAdapter?.items = it
+        searchResult?.let {
+          fragmentSearchBinding?.searchNoResults?.isVisible = it.isEmpty()
+          searchAdapter?.items = it
+        }
       }
     }
   }

core/src/main/java/org/kiwix/kiwixmobile/core/search/viewmodel/SearchState.kt

@@ -18,6 +18,7 @@
 
 package org.kiwix.kiwixmobile.core.search.viewmodel
 
+import kotlinx.coroutines.Job
 import org.kiwix.kiwixmobile.core.search.adapter.SearchListItem
 
 data class SearchState(
@@ -26,18 +27,29 @@
   val recentResults: List<SearchListItem.RecentSearchListItem>,
   val searchOrigin: SearchOrigin
 ) {
-  fun getVisibleResults(startIndex: Int): List<SearchListItem.RecentSearchListItem>? =
+  @Suppress("NestedBlockDepth")
+  fun getVisibleResults(
+    startIndex: Int,
+    job: Job? = null
+  ): List<SearchListItem.RecentSearchListItem>? =
     if (searchTerm.isEmpty()) {
       recentResults
     } else {
       searchResultsWithTerm.suggestionSearch?.let {
-        val maximumResults = it.estimatedMatches
-        val safeEndIndex =
-          if (startIndex + 100 < maximumResults) startIndex + 100 else maximumResults
-        val searchIterator =
-          it.getResults(startIndex, safeEndIndex.toInt())
         val searchResults = mutableListOf<SearchListItem.RecentSearchListItem>()
+        if (job?.isActive == false) {
+          // if the previous job is cancel then do not execute the code
+          return@getVisibleResults searchResults
+        }
+        val safeEndIndex = startIndex + 100
+        val searchIterator =
+          it.getResults(startIndex, safeEndIndex)
         while (searchIterator.hasNext()) {
+          if (job?.isActive == false) {
+            // check if the previous job is cancel while retrieving the data for previous searched item
+            // then break the execution of code.
+            break
+          }
           val entry = searchIterator.next()
           searchResults.add(SearchListItem.RecentSearchListItem(entry.title, entry.path))
         }

core/src/test/java/org/kiwix/kiwixmobile/core/search/viewmodel/SearchStateTest.kt

@@ -35,7 +35,7 @@ internal class SearchStateTest {
     val suggestionSearchWrapper: SuggestionSearchWrapper = mockk()
     val searchIteratorWrapper: SuggestionIteratorWrapper = mockk()
     val entryWrapper: SuggestionItemWrapper = mockk()
-    val estimatedMatches = 1
+    val estimatedMatches = 100
     every { suggestionSearchWrapper.estimatedMatches } returns estimatedMatches.toLong()
     // Settings list to hasNext() to ensure it returns true only for the first call.
     // Otherwise, if we do not set this, the method will always return true when checking if the iterator has a next value,