Return a Promise for `Clipboard.getString()`

Summary:
For clipboard, add error callback in Android. Code like
```javascript
Clipboard.getString((content)=>{
    //do something
},(error)=>{
   //do something for error
})
```
Closes https://github.com/facebook/react-native/pull/4792

Reviewed By: svcscm

Differential Revision: D2844937

Pulled By: nicklockwood

fb-gh-sync-id: 19953807ff07238e6a6ef5aedf1a3fcbca7e62a1

Examples/UIExplorer/ClipboardExample.js

@@ -23,23 +23,25 @@ var {
 } = React;
 
 var ClipboardExample = React.createClass({
-  getInitialState: function() {
+  getInitialState() {
     return {
       content: 'Content will appear here'
     };
   },
-  
-  _setContentToClipboard:function(){
+  async _setClipboardContent(){
     Clipboard.setString('Hello World');
-    Clipboard.getString(content => {
+    try {
+      var content = await Clipboard.getString();
       this.setState({content});
-    });
-  },
+    } catch (e) {
+      this.setState({content:e.message});
+    }
 
+  },
   render() {
     return (
       <View>
-        <Text onPress={this._setContentToClipboard} style={{color: 'blue'}}>
+        <Text onPress={this._setClipboardContent} style={{color: 'blue'}}>
           Tap to put "Hello World" in the clipboard
         </Text>
         <Text style={{color: 'red', marginTop: 20}}>
@@ -55,6 +57,8 @@ exports.description = 'Show Clipboard contents.';
 exports.examples = [
   {
     title: 'Clipboard.setString() and getString()',
-    render(): ReactElement { return <ClipboardExample />; }
+    render() {
+      return <ClipboardExample/>;
+    }
   }
 ];

Libraries/Components/Clipboard/Clipboard.js

@@ -10,4 +10,39 @@
  */
 'use strict';
 
-module.exports = require('NativeModules').Clipboard;
+var Clipboard = require('NativeModules').Clipboard;
+
+/**
+ * `Clipboard` gives you an interface for setting and getting content from Clipboard on both iOS and Android
+ */
+module.exports = {
+  /**
+   * Get content of string type, this method returns a `Promise`, so you can use following code to get clipboard content
+   * ```javascript
+   * async _getContent() {
+   *   var content = await Clipboard.getString();
+   * }
+   * ```
+   * @param this parameter is deprecated. callback is function with one argument of string type
+   */
+  getString(callback) {
+    if (callback) {
+        console.warn('Clipboard.getString(callback) is deprecated. Use the returned Promise instead');
+        Clipboard.getString().then(callback);
+        return;
+    }
+    return Clipboard.getString();
+  },
+  /**
+   * Set content of string type. You can use following code to set clipboard content
+   * ```javascript
+   * _setContent() {
+   *   Clipboard.setString('hello world');
+   * }
+   * ```
+   * @param this parameter is content that will be set into clipboard.
+   */
+  setString(content) {
+    Clipboard.setString(content);
+  }
+};

React/Modules/RCTClipboard.m

@@ -22,11 +22,6 @@ RCT_EXPORT_MODULE()
   return dispatch_get_main_queue();
 }
 
-RCT_EXPORT_METHOD(getString:(RCTResponseSenderBlock)callback)
-{
-  UIPasteboard *clipboard = [UIPasteboard generalPasteboard];
-  callback(@[RCTNullIfNil(clipboard.string)]);
-}
 
 RCT_EXPORT_METHOD(setString:(NSString *)content)
 {
@@ -34,4 +29,11 @@ RCT_EXPORT_METHOD(setString:(NSString *)content)
   clipboard.string = content;
 }
 
+RCT_EXPORT_METHOD(getString:(RCTPromiseResolveBlock)resolve
+                  rejecter:(__unused RCTPromiseRejectBlock)reject)
+{
+  UIPasteboard *clipboard = [UIPasteboard generalPasteboard];
+  resolve(@[RCTNullIfNil(clipboard.string)]);
+}
+
 @end

ReactAndroid/src/main/java/com/facebook/react/modules/clipboard/ClipboardModule.java

@@ -21,6 +21,7 @@ import com.facebook.react.bridge.ReactApplicationContext;
 import com.facebook.react.bridge.ReactContext;
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.bridge.Promise;
 import com.facebook.react.common.ReactConstants;
 
 import java.util.ArrayList;
@@ -43,28 +44,25 @@ public class ClipboardModule extends ReactContextBaseJavaModule {
   }
 
   private ClipboardManager getClipboardService() {
-    ReactApplicationContext reactContext = getReactApplicationContext(); 
-    return (ClipboardManager) reactContext.getSystemService(reactContext.CLIPBOARD_SERVICE);
+    return (ClipboardManager) getReactApplicationContext().getSystemService(getReactApplicationContext().CLIPBOARD_SERVICE);
   }
 
   @ReactMethod
-  public void getString(Callback cb) {
+  public void getString(Promise promise){
     try {
       ClipboardManager clipboard = getClipboardService();
       ClipData clipData = clipboard.getPrimaryClip();
       if (clipData == null) {
-        cb.invoke("");
-        return;
+        promise.resolve("");
       }
       if (clipData.getItemCount() >= 1) {
         ClipData.Item firstItem = clipboard.getPrimaryClip().getItemAt(0);
-        String text = "" + firstItem.getText();
-        cb.invoke(text);
+        promise.resolve("" + firstItem.getText());
       } else {
-        cb.invoke("");
+        promise.resolve("");
       }
     } catch(Exception e) {
-      FLog.w(ReactConstants.TAG, "Cannot get clipboard contents: " + e.getMessage());
+      promise.reject(e);
     }
   }