[ReactNative] Add prompt to AlertIOS

Summary:
Add `AlertIOS.prompt`

It's compatible with the js spec, with the exception that I had to add
a callback param since it's async. Also supports the same button configuration
as `AlertIOS.alert`.

@public

Test Plan:
I've updated the `AlertIOS` example on UIExplorer with every
valid combination of
parameters, so just going through it should be fine.

Examples/UIExplorer/AlertIOSExample.js

@@ -95,9 +95,98 @@ exports.examples = [{
         </TouchableHighlight>
       </View>
     );
-  },
+  }
+},
+{
+  title: 'Prompt',
+  render(): React.Component {
+    return <PromptExample />
+  }
 }];
 
+class PromptExample extends React.Component {
+  constructor(props) {
+    super(props);
+
+    this.promptResponse = this.promptResponse.bind(this);
+    this.state = {
+      promptValue: undefined,
+    };
+
+    this.title = 'Type a value';
+    this.defaultValue = 'Default value';
+    this.buttons = [{
+      text: 'Custom cancel',
+    }, {
+      text: 'Custom OK',
+      onPress: this.promptResponse
+    }];
+  }
+
+  render() {
+    return (
+      <View>
+        <Text style={{marginBottom: 10}}>
+          <Text style={{fontWeight: 'bold'}}>Prompt value:</Text> {this.state.promptValue}
+        </Text>
+
+        <TouchableHighlight
+          style={styles.wrapper}
+          onPress={this.prompt.bind(this, this.title, this.promptResponse)}>
+
+          <View style={styles.button}>
+            <Text>
+              prompt with title & callback
+            </Text>
+          </View>
+        </TouchableHighlight>
+
+        <TouchableHighlight
+          style={styles.wrapper}
+          onPress={this.prompt.bind(this, this.title, this.buttons)}>
+
+          <View style={styles.button}>
+            <Text>
+              prompt with title & custom buttons
+            </Text>
+          </View>
+        </TouchableHighlight>
+
+        <TouchableHighlight
+          style={styles.wrapper}
+          onPress={this.prompt.bind(this, this.title, this.defaultValue, this.promptResponse)}>
+
+          <View style={styles.button}>
+            <Text>
+              prompt with title, default value & callback
+            </Text>
+          </View>
+        </TouchableHighlight>
+
+        <TouchableHighlight
+          style={styles.wrapper}
+          onPress={this.prompt.bind(this, this.title, this.defaultValue, this.buttons)}>
+
+          <View style={styles.button}>
+            <Text>
+              prompt with title, default value & custom buttons
+            </Text>
+          </View>
+        </TouchableHighlight>
+      </View>
+    );
+  }
+
+  prompt() {
+    // Flow's apply support is broken: #7035621
+    ((AlertIOS.prompt: any).apply: any)(AlertIOS, arguments);
+  }
+
+  promptResponse(promptValue) {
+    this.setState({ promptValue });
+  }
+}
+
 var styles = StyleSheet.create({
   wrapper: {
     borderRadius: 5,

Libraries/Utilities/AlertIOS.js

@@ -12,6 +12,7 @@
 'use strict';
 
 var RCTAlertManager = require('NativeModules').AlertManager;
+var invariant = require('invariant');
 
 var DEFAULT_BUTTON_TEXT = 'OK';
 var DEFAULT_BUTTON = {
@@ -47,14 +48,17 @@ class AlertIOS {
     message?: ?string,
     buttons?: Array<{
       text: ?string;
-      onPress: ?Function;
+      onPress?: ?Function;
-    }>
+    }>,
+    type?: ?string
   ): void {
     var callbacks = [];
     var buttonsSpec = [];
     title = title || '';
     message = message || '';
     buttons = buttons || [DEFAULT_BUTTON];
+    type = type || '';
+
     buttons.forEach((btn, index) => {
       callbacks[index] = btn.onPress;
       var btnDef = {};
@@ -65,12 +69,50 @@ class AlertIOS {
       title,
       message,
       buttons: buttonsSpec,
-    }, (id) => {
+      type,
+    }, (id, value) => {
       var cb = callbacks[id];
-      cb && cb();
+      cb && cb(value);
     });
   }
 
+  static prompt(
+    title: string,
+    value?: string,
+    buttons?: Array<{
+      text: ?string;
+      onPress?: ?Function;
+    }>,
+    callback?: ?Function
+  ): void {
+    if (arguments.length === 2) {
+      if (typeof value === 'object') {
+        buttons = value;
+        value = undefined;
+      } else if (typeof value === 'function') {
+        callback = value;
+        value = undefined;
+      }
+    } else if (arguments.length === 3 && typeof buttons === 'function') {
+      callback = buttons;
+      buttons = undefined;
+    }
+
+    invariant(
+      !(callback && buttons) && (callback || buttons),
+      'Must provide either a button list or a callback, but not both'
+    );
+
+    if (!buttons) {
+      buttons = [{
+        text: 'Cancel',
+      }, {
+        text: 'OK',
+        onPress: callback
+      }];
+    }
+    this.alert(title, value, buttons, 'plain-text');
+  }
 }
 
 module.exports = AlertIOS;

React/Modules/RCTAlertManager.m

@@ -59,6 +59,7 @@ RCT_EXPORT_METHOD(alertWithArgs:(NSDictionary *)args
 {
   NSString *title = args[@"title"];
   NSString *message = args[@"message"];
+  NSString *type = args[@"type"];
   NSArray *buttons = args[@"buttons"];
 
   if (!title && !message) {
@@ -70,13 +71,20 @@ RCT_EXPORT_METHOD(alertWithArgs:(NSDictionary *)args
   }
 
   UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title
-                                                      message:message
+                                                      message:nil
                                                      delegate:self
                                             cancelButtonTitle:nil
                                             otherButtonTitles:nil];
 
   NSMutableArray *buttonKeys = [[NSMutableArray alloc] initWithCapacity:buttons.count];
 
+  if ([type isEqualToString:@"plain-text"]) {
+    alertView.alertViewStyle = UIAlertViewStylePlainTextInput;
+    [alertView textFieldAtIndex:0].text = message;
+  } else {
+    alertView.message = message;
+  }
+
   NSInteger index = 0;
   for (NSDictionary *button in buttons) {
     if (button.count != 1) {
@@ -108,7 +116,15 @@ RCT_EXPORT_METHOD(alertWithArgs:(NSDictionary *)args
 
   RCTResponseSenderBlock callback = _alertCallbacks[index];
   NSArray *buttonKeys = _alertButtonKeys[index];
-  callback(@[buttonKeys[buttonIndex]]);
+  NSArray *args;
+
+  if (alertView.alertViewStyle == UIAlertViewStylePlainTextInput) {
+    args = @[buttonKeys[buttonIndex], [alertView textFieldAtIndex:0].text];
+  } else {
+    args = @[buttonKeys[buttonIndex]];
+  }
+
+  callback(args);
 
   [_alerts removeObjectAtIndex:index];
   [_alertCallbacks removeObjectAtIndex:index];