wip: Introduces TextController.asMutableTextFieldValueState.

Author: rjrjr

samples/compose-samples/src/androidTest/java/com/squareup/sample/compose/textinput/TextInputTest.kt

@@ -1,6 +1,5 @@
 package com.squareup.sample.compose.textinput
 
-import androidx.compose.ui.test.ExperimentalTestApi
 import androidx.compose.ui.test.assertTextEquals
 import androidx.compose.ui.test.hasSetTextAction
 import androidx.compose.ui.test.junit4.createAndroidComposeRule
@@ -30,7 +29,6 @@ class TextInputTest {
     .around(composeRule)
     .around(IdlingDispatcherRule)
 
-  @OptIn(ExperimentalTestApi::class)
   @Test
   fun allowsTextEditing() {
     runBlocking {

samples/compose-samples/src/main/java/com/squareup/sample/compose/textinput/TextInputViewFactory.kt

@@ -20,6 +20,7 @@ import com.squareup.sample.compose.textinput.TextInputWorkflow.Rendering
 import com.squareup.workflow1.ui.TextController
 import com.squareup.workflow1.ui.compose.ScreenComposableFactory
 import com.squareup.workflow1.ui.compose.asMutableState
+import com.squareup.workflow1.ui.compose.asMutableTextFieldValueState
 import com.squareup.workflow1.ui.compose.tooling.Preview
 
 val TextInputComposableFactory = ScreenComposableFactory<Rendering> { rendering ->
@@ -30,14 +31,14 @@ val TextInputComposableFactory = ScreenComposableFactory<Rendering> { rendering
       .animateContentSize(),
     horizontalAlignment = Alignment.CenterHorizontally
   ) {
-    var text by rendering.textController.asMutableState()
+    var textFieldValue by rendering.textController.asMutableTextFieldValueState()
 
-    Text(text = text)
+    Text(text = textFieldValue.text)
     OutlinedTextField(
       label = {},
       placeholder = { Text("Enter some text") },
-      value = text,
-      onValueChange = { text = it }
+      value = textFieldValue,
+      onValueChange = { textFieldValue = it }
     )
     Spacer(modifier = Modifier.height(8.dp))
     Button(onClick = rendering.onSwapText) {

workflow-ui/compose/src/main/java/com/squareup/workflow1/ui/compose/TextControllerAsMutableTextFieldValueState.kt

@@ -0,0 +1,78 @@
+package com.squareup.workflow1.ui.compose
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.MutableState
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.snapshotFlow
+import androidx.compose.ui.text.TextRange
+import androidx.compose.ui.text.input.TextFieldValue
+import com.squareup.workflow1.ui.TextController
+import kotlinx.coroutines.launch
+
+/**
+ * A wrapper extension for [com.squareup.workflow1.ui.compose.asMutableState] that returns
+ * [TextFieldValue]. This makes it easy to use it with `MarketTextField` since `MarketTextField`
+ * expects [TextFieldValue].
+ *
+ * @param selectionStart The starting index of the selection.
+ * @param selectionEnd The ending index of the selection.
+ *
+ * If [selectionStart] equals [selectionEnd] then nothing is selected, and the cursor is placed at
+ * [selectionStart]. By default, the cursor will be placed at the end of the text.
+ *
+ * Usage:
+ *
+ *    var fooText by fooTextController.asMutableTextFieldValueState()
+ *    BasicTextField(
+ *      value = fooText,
+ *      onValueChange = { fooText = it },
+ *    )
+ *
+ */
+@Composable
+public fun TextController.asMutableTextFieldValueState(
+  selectionStart: Int = textValue.length,
+  selectionEnd: Int = selectionStart,
+): MutableState<TextFieldValue> {
+  val textFieldValue = remember(this) {
+    val actualStart = selectionStart.coerceIn(0, textValue.length)
+    val actualEnd = selectionEnd.coerceIn(actualStart, textValue.length)
+    mutableStateOf(
+      TextFieldValue(
+        text = textValue,
+        // We need to set the selection manually when creating  new `TextFieldValue` whenever
+        // `TextController` changes because the text inside may not be empty.
+        selection = TextRange(actualStart, actualEnd),
+      )
+    )
+  }
+
+  LaunchedEffect(this) {
+    launch {
+      // This is to address the case when value of `TextController` is updated within the workflow.
+      // By subscribing directly to `onTextChanged` we can use this to also update the textFieldValue.
+      onTextChanged
+        .collect { newText ->
+          // Only update the `textFieldValue` if the new text is different from the current text.
+          // This ensures the selection is maintained when the text is updated from the UI side,
+          // and is only reset when the text is changed via `TextController`.
+          if (textFieldValue.value.text != newText) {
+            textFieldValue.value = TextFieldValue(
+              text = newText,
+              selection = TextRange(newText.length),
+            )
+          }
+        }
+    }
+
+    // Update this `TextController`'s text whenever the `textFieldValue` changes.
+    snapshotFlow { textFieldValue.value }
+      .collect { newText ->
+        textValue = newText.text
+      }
+  }
+
+  return textFieldValue
+}

workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/TextController.kt

@@ -26,7 +26,7 @@ import kotlinx.coroutines.flow.drop
  *    function for your UI platform, e.g.:
  *
  *    - `control()` for an Android EditText view
- *    - `asMutableState()` from an Android `@Composable` function
+ *    - `asMutableState()` or `asMutableTextFieldValueState()` in an Android `@Composable` function
  *
  * If your workflow needs to access or change the current text value, get the value from [textValue].
  * If your workflow needs to react to changes, it can observe [onTextChanged] by converting it to a