1.WebView的介紹

    webview是Android中直接載入html頁面的控制元件，它為webApp帶來了新生命。那麼，他的出現也伴隨著很多問題的產生；今天就webview的載入及快取方面的知識做個總結，希望對大家有所幫助。
2.Webview的快取

 <uses-permission android:name="android.permission.INTERNET"/>
 <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
 <uses-permissi on android:name="android.permission.READ_EXTERNAL_STORAGE"/>
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
 
/>

WebSettings webSettings = myWebView.getSettings();
//設定渲染的優先順序
webSettings.setRenderPriority(WebSettings.RenderPriority.HIGH);
// 開啟 DOM storage API 功能
webSettings.setDomStorageEnabled(true);
//開啟 database storage API 功能
webSettings.setDatabaseEnabled(true);
String cacheDirPath = 
 
getFilesDir().getAbsolutePath() + APP_CACAHE_DIRNAME;
//設定資料庫快取路徑
webSettings.setDatabasePath(cacheDirPath);
//設定  Application Caches 快取目錄
webSettings.setAppCachePath(cacheDirPath);
//開啟 Application Caches 功能
webSettings.setAppCacheEnabled(true);

webSettings.setLoadWithOverviewMode(true);
//設定WebView支援JavaScript
webSettings.setJavaScriptEnabled(true);
//設定可以訪問檔案
webSettings.setAllowFileAccess(true);
//設定支援縮放
webSettings.setBuiltInZoomControls(true);
webSettings.setDefaultTextEncodingName("UTF-8");

/**
 * 檢測當前網路可用
*
 * @param context
* @return
*/
public static boolean isNetworkAvailable(Context context) {
    ConnectivityManager connectivity = (ConnectivityManager) context
.getSystemService(Context.CONNECTIVITY_SERVICE);
    if (connectivity != null) {
        NetworkInfo info = connectivity.getActiveNetworkInfo();
        if (info != null && info.isConnected()) {
            // 當前網路是連線的
if (info.getState() == NetworkInfo.State.CONNECTED) {
                // 當前所連線的網路可用
return true;
            }
        }
    }
    return false;
}

if (isNetworkAvailable(getApplicationContext())) {
    //有網路連線，設定預設快取模式
webSettings.setCacheMode(WebSettings.LOAD_DEFAULT);
} else {
    //無網路連線，設定本地快取模式
webSettings.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
}

WebSettings.LOAD_DEFAULT

WebSettings.LOAD_CACHE_ELSE_NETWORK

3.WebView的記憶體洩漏

首先宣告，webview如果不做任何處理的話，會存在記憶體洩漏的風險；規範的程式碼，一般對webview都做了防止OOM的處理的。

1.先從佈局下手，動態建立WebView

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.zhangxing.webviewcachedemo.MainActivity">
   <LinearLayout
android:id="@+id/webview_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
   </LinearLayout>
</RelativeLayout>

webViewLayout = (LinearLayout) findViewById(R.id.webview_layout);
myWebView = new WebView(getApplicationContext());
webViewLayout.addView(myWebView);

@Override
protected void onDestroy() {
    super.onDestroy();
    myWebView.removeAllViews();
    myWebView.destroy();
}

//設定WebView支援JavaScript
webSettings.setJavaScriptEnabled(true);

webSettings.setJavaScriptCanOpenWindowsAutomatically(true);
myWebView.requestFocus();

myWebView.setWebChromeClient(new WebChromeClient(){
    @Override
public void onProgressChanged(WebView view, int newProgress) {
        super.onProgressChanged(view, newProgress);
        if(newProgress == 100){
            if(dialog != null && dialog.isShowing()){
                dialog.dismiss();
            }
        }else{
            if(dialog == null){
                dialog = new ProgressDialog(MainActivity.this);
                dialog.setTitle("正在載入中.....");
                dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                dialog.setProgress(newProgress);
                dialog.show();
            }else{
                dialog.setProgress(newProgress);
            }
        }
    }
});

/**
 * WebViewClient幫助webView處理一些頁面控制和請求通知
* 當點選webview控制元件中的連結時,在這裡設定顯示在webview中,否則,會在瀏覽器開啟
*/
myWebView.setWebViewClient(new WebViewClient() {
    @Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
        //設定網頁在webview控制元件中開啟,false在瀏覽器中開啟
view.loadUrl(url);
        return true;
    }
});