Add TextInput.setSelection method

Summary:
Adds a `setSelection` imperative method to `TextInput`.

Changelog:
[General][Added] - Adds a setSelection imperative method to TextInput

Reviewed By: JoshuaGross

Differential Revision: D32186514

fbshipit-source-id: 549a7d93b1c55363cf01d804b1e3d735e55c4481

Libraries/Components/TextInput/TextInput.js

@@ -766,6 +766,7 @@ type ImperativeMethods = $ReadOnly<{|
   clear: () => void,
   isFocused: () => boolean,
   getNativeRef: () => ?React.ElementRef<HostComponent<mixed>>,
+  setSelection: (start: number, end: number) => void,
 |}>;
 
 const emptyFunctionThatReturnsTrue = () => true;
@@ -1009,6 +1010,18 @@ function InternalTextInput(props: Props): React.Node {
     }
   }
 
+  function setSelection(start: number, end: number): void {
+    if (inputRef.current != null) {
+      viewCommands.setTextAndSelection(
+        inputRef.current,
+        mostRecentEventCount,
+        null,
+        start,
+        end,
+      );
+    }
+  }
+
   // TODO: Fix this returning true on null === null, when no input is focused
   function isFocused(): boolean {
     return TextInputState.currentlyFocusedInput() === inputRef.current;
@@ -1049,6 +1062,7 @@ function InternalTextInput(props: Props): React.Node {
         ref.clear = clear;
         ref.isFocused = isFocused;
         ref.getNativeRef = getNativeRef;
+        ref.setSelection = setSelection;
       }
     },
   });

packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js

@@ -377,7 +377,7 @@ class SelectionExample extends React.Component<
   $FlowFixMeProps,
   SelectionExampleState,
 > {
-  _textInput: any;
+  _textInput: React.ElementRef<typeof TextInput> | null = null;
 
   constructor(props) {
     super(props);
@@ -397,8 +397,11 @@ class SelectionExample extends React.Component<
   }
 
   select(start, end) {
-    this._textInput.focus();
+    this._textInput?.focus();
     this.setState({selection: {start, end}});
+    if (this.props.imperative) {
+      this._textInput?.setSelection(start, end);
+    }
   }
 
   selectRandom() {
@@ -430,7 +433,7 @@ class SelectionExample extends React.Component<
             // $FlowFixMe[method-unbinding] added when improving typing for this parameters
             onSelectionChange={this.onSelectionChange.bind(this)}
             ref={textInput => (this._textInput = textInput)}
-            selection={this.state.selection}
+            selection={this.props.imperative ? undefined : this.state.selection}
             style={this.props.style}
             value={this.state.value}
           />
@@ -666,4 +669,27 @@ module.exports = ([
       );
     },
   },
+  {
+    title: 'Text selection & cursor placement (imperative)',
+    name: 'cursorPlacementImperative',
+    render: function (): React.Node {
+      return (
+        <View>
+          <SelectionExample
+            testID="singlelineImperative"
+            style={styles.default}
+            value="text selection can be changed imperatively"
+            imperative={true}
+          />
+          <SelectionExample
+            testID="multilineImperative"
+            multiline
+            style={styles.multiline}
+            value={'multiline text selection\ncan also be changed imperatively'}
+            imperative={true}
+          />
+        </View>
+      );
+    },
+  },
 ]: Array<RNTesterModuleExample>);