Minstrel

A Javascript bridge for android that accepts all parameter types (object, functions, etc) and handles return values with the same flexibility

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Why?

Out of the box, Android's WebView visual component has many limitations when bridging Javascript to Java, mostly around the following:

• Interaction from Java->Javascript requires loadUrl("javascript:")
• Interaction from Javascript->Java only accepts Strings, Doubles, Integers and Booleans. No Objects, Functions, etc are handled, resulting in a parameter of 'undefined'. This is very limiting as Javascript devs often want to pass in callbacks, objects, etc.
• Calling a javascript function from Java does not allow for receiving a return value in earlier SDKs. This is mitigated somewhat by the addition of evaluateJavascript, but even then, the return value can only be a string.

Introduction

This library brings Android's webview/bridge support very much on par with iOS's JavascriptCore framework. It allows for parameters to be passed to and from Javascript of any type.

ie: This now works when calling from Javascript back to the native app. The app will then execute the callback (2nd parameter) upon completion.

android.updateRecords({ name: "Herbert", age: 22 }, function (status) { updateWebUI(status); });

Usage

• Instead of using a WebView, replace it with an instance of JSWebView.
• To export your objects and methods, continue calling addJavascriptInterface() as you normally would.
• For all exported objects and methods, all parameters should be Strings (see below).
• You'll then need to wrap those parameters with JSValue: ie: JSValue jsParam = JSValue(param);

Example:

Imagine this is called from Javascript ...

android.doSomething(function (n) { return n * n; });

In your Activity ...

  webView.addJavascriptInterface(new Bridge(this, webView), "android");

In the interface you wish to export ...

public class Bridge {
    final Context mContext;
    JSWebView mWebView; // we need the webview in order to call functions.

    Bridge(Context context, JSWebView webView) {
        mContext = context;
        mWebView = webView;
    }

    @JavascriptInterface
    public void doSomething2(String param) {
        // turn the parameter we got into something useful.
        JSValue valueParam = new JSValue(param);

        // is it a function?  if so, lets call it.
        if (valueParam.isFunction()) {
            Object args[] = {5};

            // call said function against mWebView, with the given args.
            // the ValueCallback will be executed once the called function returns.
            valueParam.callFunction(mWebView, args, new ValueCallback<JSValue>() {
                @Override
                public void onReceiveValue(final JSValue value) {
                    // did we actually get back a value?  (ie: not null or undefined)
                    if (value.isValid()) {
                        // do something with your value of 25
                        Log.d("value", value.stringValue());
                    }
                }
            });
        }
    }
    
}

How does it work?

Essentially it creates a proxy object in Javascript for everything you export, which turns all parameters/returns into JSON. We then pass the JSON to and fro as Strings, decode them, etc. Please have a look at the source and let me know if you have further questions.

Contributions

We appreciate your contributions to all of our projects and look forward to interacting with you via Pull Requests, the issue tracker, via Twitter, etc. We're happy to help you, and to have you help us. We'll strive to answer every PR and issue and be very transparent in what we do.

When contributing code, please refer to our Dennis (https://github.com/TheHolyGrail/Dennis).

THG's Primary Contributors

Dr. Sneed (@bsneed)
Steve Riggins (@steveriggins)
Sam Grover (@samgrover)
Angelo Di Paolo (@angelodipaolo)
Cody Garvin (@migs647)
Wes Ostler (@wesostler)

License

The MIT License (MIT)

Copyright (c) 2015 Walmart, TheHolyGrail, and other Contributors

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.