如何獲取WebView的內容寬度[翻譯]

原文網址：http://android.pimmos.com/2011/03/24/how-to-retrieve-the-contentwidth-of-a-webview/

The extensive Android SDK allows you to do many great things with particular views like the WebView for displaying webpages on Android powered devices.
Android SDK 的擴展，經過使用特定的view，容許你作許多事情。好比，WebView，用來在Android手機上展現網頁。

As of lately while I was experimenting with the Android SDK I was using a WebView in one of my activities.
最近，我在體驗Android SDK的時候，在一個Activity中用到了WebView。

From that particular WebView I needed to know the ContentHeight but also the ContentWidth.
從WebView，我不但想要知道ContentHeight，還想知道ContentWidth。

Now getting the contentHeight is easy like so:
如今的狀況是：獲取contentHeight很easy，以下：

webview.getContentHeight();

Unfortunately getting the contentWidth from a WebView is rather more difficult, since there is not a simple method like:
不幸的是，從一個WebView獲取contentWidth是至關困難，由於SDK中沒有一個像這樣的方法：

// THIS METHOD DOES NOT EXIST!
webview.getContentWidth();

There are ways to get the contentWidth of the rendered HTML page and that is through Javascript. If Javascript can get it for you, then you can also have them in your Java code within your Android App.
固然是有方法獲取contentWidth的，就是經過Javascript來獲取。若是你可以支持Javascript，那麼你就能夠在你的Android 程序中，使用java代碼來獲取寬度。

By using a JavascriptInterface with your WebView you can let Javascript communicate with your Android App Java code by invoking methods on a registered object that you can embed using the JavascriptInterface.
經過在你的WebView中使用JavascriptInterface，經過調用你註冊的JavascriptInterface方法，可讓Javascript和你的Android程序的java代碼相互連通。
 
So how does this work?
怎麼作呢？

For a quick example I created a simple Activity displaying a webview that loads a webpage wich displays a log message and a Toast message with the contentWidth wich was determined using Javascript. Note that this happens AFTER the page was finished loading, because before the page is finished loading the width might not be fully rendered. Also keep in mind that if there is content loaded asynchronously that it doesn't affect widths (most likely only heights will be affected as the width is almost always fully declared in CSS files unless you have a 100% width webpage).
搭建一個快速的例子：建立一個簡單的展現webView的Activity，一個LogCat消息，一個Toast消息，用來顯示咱們經過Javascript獲取的寬度。注意：這些會在網頁徹底加載以後顯示，由於在網頁加載完成以前，寬度可能不可以正確的獲取到。同時也要注意到，若是是異步加載，這並不影響寬度（最多高度會受影響，由於寬度老是在CSS文件中作了徹底的定義，除非在網頁中你用了100%寬度。）。

Below is the code of the Activity Main.java:
下面的代碼是Activity的代碼：

Main.java

package com.pimmos.android.samples.webviewcontentwidth;   
import android.app.Activity; 
import android.os.Bundle; 
import android.util.Log; 
import android.webkit.WebView; 
import android.webkit.WebViewClient; 
import android.widget.Toast;   
public class Main extends Activity {       
    private final static String LOG_TAG = "WebViewContentWidth";
    private final Activity activity = this;   
    private static int webviewContentWidth = 0;
    private static WebView webview;       

/** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);   
         webview = (WebView) findViewById(R.id.webview);
         webview.getSettings().setJavaScriptEnabled(true);
         webview.setSaveEnabled(true);
         webview.addJavascriptInterface(new JavaScriptInterface(), "HTMLOUT");
         webview.setWebViewClient(new WebViewClient() {
             @Override
            public void onPageFinished(WebView view, String url) {
                 webview.loadUrl("javascript:window.HTMLOUT.getContentWidth(document.getElementsByTagName('html')[0].scrollWidth);");
             }
         });
         webview.loadUrl("http://www.pimmos.com/");
     }

     class JavaScriptInterface {
         public void getContentWidth(String value) {
             if (value != null) {
                 webviewContentWidth = Integer.parseInt(value);
                 Log.d(LOG_TAG, "Result from javascript: " + webviewContentWidth);
                 Toast.makeText(                         activity,
                         "ContentWidth of webpage is: " +
webviewContentWidth                                 + 
"px", Toast.LENGTH_SHORT).show();
             }
         }
     }
}

Below is the XML layout used with the Activity wich only contains a simple WebView:
下面是Activity的Layout，主要就是一個簡單的WebView：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout
   xmlns:android="http://schemas.android.com/apk/res/android"    
   android:orientation="vertical" 
   android:layout_width="fill_parent"    
   android:layout_height="fill_parent">
  
   <WebView android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
 </LinearLayout>

AndroidManifest.xml layout:
AndroidManifest.xml代碼：

<?xml version="1.0" encoding="utf-8"?> 
<manifest
 xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.pimmos.android.samples.webviewcontentwidth"
    android:versionCode="1" android:versionName="1.0">
     <application android:icon="@drawable/icon"
 android:label="@string/app_name">
         <activity android:name=".Main"
 android:label="@string/app_name">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category 
android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
       </application>
     <uses-sdk android:minSdkVersion="7" />
     <uses-permission android:name="android.permission.INTERNET" />
   </manifest>

You can also download the full source of Android Application - WebViewContentWidth!
你也能夠到這裏下載所有的源代碼 -  WebViewContentWidth!