How to Correctly Call JavaScript Functions from an Android WebView?

Calling JavaScript Functions from an Android WebView

When trying to access and execute JavaScript functions within a WebView component in an Android application, some may encounter difficulties. Let's address a common problem: unsuccessful attempts to call JavaScript functions.

In your code, you aimed to invoke a JavaScript function named "testEcho" from the Android app and have it call back a Java function that displays a toast message. Following your provided code, we will identify the error and provide a solution.

Identified Issue:

The error lies in the syntax of the JavaScript function call within the Android app. The testEcho() function is missing proper string quotes around its parameter.

Solution:

To resolve this issue and successfully call the JavaScript function, use the following corrected JavaScript function call:

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

By adding the missing quotes around the parameter, the Android app can now correctly pass a message to the JavaScript function, triggering the desired behavior.

Additional Considerations:

You mentioned using external JavaScript files in your HTML. While this is generally not an issue, ensure that the required files are correctly referenced and loaded within the WebView. You can use the following code to check if the external JavaScript files are loading successfully:

WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
webSettings.setUserAgentString("myAndroidAgent");

By enabling JavaScript and setting a custom user agent string, you increase the compatibility and stability of the WebView.

In summary, the missing quotes around the parameter in the testEcho() function call caused the unsuccessful execution of the JavaScript function. After correcting the JavaScript function call and considering the loading of external JavaScript files, you should be able to successfully call JavaScript functions from your Android WebView.

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