Add Android WebView

examples/webview/pyproject.toml

@@ -18,8 +18,7 @@ requires = []
 
 [tool.briefcase.app.webview.macOS]
 requires = [
-'../../src/core',
-'../../src/cocoa',
+    'toga-cocoa',
 ]
 
 [tool.briefcase.app.webview.linux]
@@ -35,8 +34,7 @@ requires = [
 # Mobile deployments
 [tool.briefcase.app.webview.iOS]
 requires = [
-'../../src/core',
-'../../src/ios',
+    'toga-ios',
 ]
 
 [tool.briefcase.app.webview.android]

src/android/toga_android/factory.py

@@ -14,6 +14,7 @@
 from .widgets.slider import Slider
 from .widgets.switch import Switch
 from .widgets.textinput import TextInput
+from .widgets.webview import WebView
 from .window import Window
 
 
@@ -38,6 +39,7 @@ def not_implemented(feature):
     "Slider",
     "Switch",
     "TextInput",
+    "WebView",
     "Window",
     "not_implemented",
     "paths",

src/android/toga_android/libs/android_widgets.py

@@ -25,8 +25,11 @@
 TextWatcher = JavaInterface("android/text/TextWatcher")
 TypedValue = JavaClass("android/util/TypedValue")
 Typeface = JavaClass("android/graphics/Typeface")
+ValueCallback = JavaInterface("android/webkit/ValueCallback")
 ViewGroup__LayoutParams = JavaClass("android/view/ViewGroup$LayoutParams")
 View__MeasureSpec = JavaClass("android/view/View$MeasureSpec")
+WebView = JavaClass("android/webkit/WebView")
+WebViewClient = JavaClass("android/webkit/WebViewClient")
 
 # Indicate to `rubicon-java` that `ArrayAdapter` can also be typecast into a
 # `SpinnerAdapter`. This is required until `rubicon-java` explores the interfaces

src/android/toga_android/widgets/webview.py

@@ -0,0 +1,87 @@
+import asyncio
+import base64
+
+from travertino.size import at_least
+
+from ..libs import android_widgets
+from .base import Widget, align
+
+
+class ReceiveString(android_widgets.ValueCallback):
+    def __init__(self, fn=None):
+        super().__init__()
+        self._fn = fn
+
+    def onReceiveValue(self, value):
+        if self._fn:
+            if value is None:
+                self._fn(None)
+            else:
+                # Ensure we send a string to the function.
+                self._fn(value.toString())
+
+
+class WebView(Widget):
+    def create(self):
+        self.native = android_widgets.WebView(self._native_activity)
+        # Set a WebViewClient so that new links open in this activity,
+        # rather than triggering the phone's web browser.
+        self.native.setWebViewClient(android_widgets.WebViewClient())
+        # Enable JS.
+        self.native.getSettings().setJavaScriptEnabled(True)
+
+    def set_on_key_down(self, handler):
+        # Android isn't a platform that usually has a keyboard attached, so this is unimplemented for now.
+        self.interface.factory.not_implemented('WebView.set_on_key_down()')
+
+    def set_on_webview_load(self, handler):
+        # This requires subclassing WebViewClient, which is not yet possible with rubicon-java.
+        self.interface.factory.not_implemented('WebView.set_on_webview_load()')
+
+    def get_dom(self):
+        # Android has no straightforward way to get the DOM from the browser synchronously.
+        self.interface.factory.not_implemented('WebView.get_dom()')
+
+    def set_url(self, value):
+        if value:
+            self.native.loadUrl(str(value))
+
+    def set_content(self, root_url, content):
+        # Android WebView lacks an underlying set_content() primitive, so we navigate to
+        # a data URL. This means we ignore the root_url parameter.
+        data_url = ("data:text/html; charset=utf-8; base64," +
+                    base64.b64encode(content.encode('utf-8')).decode('ascii'))
+        self.set_url(data_url)
+
+    def set_user_agent(self, value):
+        if value is not None:
+            self.native.getSettings().setUserAgentString(value)
+
+    async def evaluate_javascript(self, javascript):
+        js_value = asyncio.Future()
+        self.native.evaluateJavascript(str(javascript), ReceiveString(js_value.set_result))
+        return await js_value
+
+    def invoke_javascript(self, javascript):
+        print("omg trying to invoke " + repr(javascript))
+        self.native.evaluateJavascript(str(javascript), ReceiveString())
+
+    def set_alignment(self, value):
+        # Refuse to set alignment unless widget has been added to a container.
+        # This is because this widget's setGravity() requires LayoutParams before it can be called.
+        if self.native.getLayoutParams() is None:
+            return
+        self.native.setGravity(android_widgets.Gravity.CENTER_VERTICAL | align(value))
+
+    def rehint(self):
+        self.interface.intrinsic.width = at_least(self.interface.MIN_WIDTH)
+        # Refuse to call measure() if widget has no container, i.e., has no LayoutParams.
+        # Android's measure() throws NullPointerException if the widget has no LayoutParams.
+        if self.native.getLayoutParams() is None:
+            return
+        self.native.measure(
+            android_widgets.View__MeasureSpec.UNSPECIFIED,
+            android_widgets.View__MeasureSpec.UNSPECIFIED,
+        )
+        self.interface.intrinsic.width = at_least(self.native.getMeasuredWidth())
+        self.interface.intrinsic.height = self.native.getMeasuredHeight()