- The basis upon which you can do followings within your Activity:
- Roll your own web browser.
- Simply display some online content.
- Uses the same rendering and JavaScript engine(WebKit) as the browser, but it runs under the control of your application.
- By default:
- A WebView provides no browser-like widgets.
- No zoom in and out.
- WebSettings.setBuiltInZoomControls(boolean) (introduced in API 3)
- Does not enable JavaScript.
- WebSettings.setJavaScriptEnabled()
- No navigation controls.
- Need to handle the BACK button on the device
- Overrides URL loading, it automatically accumulates a history of visited web pages.
- Web page errors are ignored.
- Perform text searches. (?)
- No address bar.
- As you click a link, by default WebView will ask Activity Manager to choose the proper handler for the url.
- Instead of adding an intent filter to view web pages, you can override the WebViewClient class and enable this Activity to handle its own URL requests.
Load content
- Can download content from the web.
- Can come from local files stored in your assets directory.
- Can even be dynamically generated by your application code.
- ex:
webview.loadUrl("http://www.google.com.tw/");
// or
String summary = "You scored 192 points.";
webview.loadData(summary, "text/html", null);
Note:
- public void loadData (String data, String mimeType, String encoding)
- This API has JavaScript's same origin policy restriction.
- 此頁面中的 script 此能用 "data" 的 schema 去存取。
- ex: data 的 schema 為 "http"，則不能使用 "https"
- 因此提供了另一個 API
A WebView has several customization points where you can add your own behavior. These are:
- Creating and setting a WebChromeClient subclass.
- This class is called when something that might impact a browser UI happens, ex:
- Progress update.
- JavaScript alerts are sent here.
- Creating and setting a WebViewClient subclass.
- It will be called when things happen that impact the rendering of the content, ex:
- Errors or form submissions.
- Will load any URL selected from this WebView into the same WebView.
- Can intercept URL loading here (via shouldOverrideUrlLoading()).
- 預設點擊頁面上的 link 會由系統處理，開啟相對應的 app。
- ex: 若是 URL 則開啟系統 Browser。
- 但若 override shouldOverrideUrlLoading()
- 則能依照自己意思判斷 URL 決定要在 WebView 開啟或是在 Browser 中開啟。ex:
- return true
- The method has handled the URL and the event should not propagate.
- ex: an Intent would be created that's handled by the Browser application
- 表示會自己處理 url。
- 因此若沒有任何處理動作，點擊後不會有反應。
- return false
- The current WebView handles the url
- 仍由系統處理，但會開啟在當前的 WebView。
- 因此若有設定自己的執行動作又 return false，則兩種執行動作都會被觸發。
- 所以如果想要畫面都在 WebView 中開啟，則表示一定要 override shouldOverrideUrlLoading()。
- Related JavaScript
- Enabling JavaScript with setJavaScriptEnabled() (Modifying the WebSettings)
- addJavascriptInterface(Object, String)
- Adding JavaScript-to-Java interfaces.
- Has security issue.
- Bind Java objects into the WebView so they can be controlled from the web pages JavaScript.
- ex: Your JavaScript code can call a method in your Android code to display a Dialog, instead of using JavaScript's alert() function.
Data
- For obvious security reasons, your application has its own cache, cookie store etc.—it does not share the Browser application's data.
- Cookies are managed on a separate thread, so operations like index building don't block the UI thread.
- CookieSyncManager
- Is used to synchronize the browser cookie store between RAM and permanent storage.
- To get the best performance, browser cookies are saved in RAM. A separate thread saves the cookies between, driven by a timer.
- Note that even sync() happens asynchronously, so don't do it just as your activity is shutting down.
Note
- Must claim this permission in AndroidManifest.xml or you won't open page and do not get any exception.
- <uses-permission android:name="android.permission.INTERNET">
Related
[AndroidLayout] WebView Performance
* Reference
- WebView | Android Developers
- WebViewClient | Android Developers
- WebChromeClient
- WebSettings | Android Developers
- CookieSyncManager | Android Developers
- Android Developers Blog: Using WebViews
- Building Web Apps in WebView | Android Developers
- WebView 1 - 4 ***
- SOP - Same Origin Policy (Browser Security Policy)
