Calling JavaScript Functions from Android in WebViews

In this article, we address a common challenge faced by Android developers: calling JavaScript functions from native Android code within WebViews.

Issue: Calling JavaScript Functions from WebView

A developer is attempting to invoke a JavaScript function from their Android application and display the output using a toast. However, their attempts to execute the JavaScript function using the loadUrl() method have been unsuccessful.

Troubleshooting and Solution

The issue stems from incorrect syntax in the JavaScript function call. By adding quotes to the parameter of the testEcho() function, the call becomes valid:

myWebView.loadUrl("javascript:testEcho('Hello World!')");

Explanation

In JavaScript, function parameters must be enclosed in quotes. Neglecting to do so results in the syntax error encountered by the developer.

Additional considerations

External JavaScript Files:

The developer mentioned referencing external JavaScript files in their HTML code. While these files may be necessary for the functionality of the web page, they should not affect the ability to call JavaScript functions from the Android application.

Other Possible Issues:

• Disabled JavaScript: Ensure that JavaScript is enabled in the WebView using the following line:

myWebView.getSettings().setJavaScriptEnabled(true);

• Java Interface Registration: Make sure to register the Java class containing the methods to be exposed to JavaScript using the following method:

myWebView.addJavascriptInterface(myJSInterface, "JSInterface");

• Incorrect Function Name: Verify that the name of the JavaScript function matches the name of the exposed function in the Java interface.

Conclusion

By correcting the syntax of the JavaScript function call and considering other potential issues, developers can successfully invoke JavaScript functions from within Android WebViews and bridge the communication gap between native and web code.