HTML5 Canvas 支持和 Android Webview
Posted
技术标签:
【中文标题】HTML5 Canvas 支持和 Android Webview【英文标题】：HTML5 Canvas Support and Android Webview 【发布时间】：2012-08-28 02:06:24 【问题描述】：我需要在我的应用程序中绘制图表。为此，我使用 RGraph (http://www.rgraph.net/)；它允许使用 javascript 绘制交互式图表。我将我的 javascript 代码放在应用程序资产中的 html 文档中，然后从 ViewPager 中的片段中调用它。
这是 HTML 和 javascript 代码：
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<html>
<head>
<script src="./libraries/RGraph.common.core.js" ></script>
<script src="./libraries/RGraph.common.dynamic.js" ></script>
<script src="./libraries/RGraph.common.tooltips.js" ></script>
<script src="./libraries/RGraph.common.effects.js" ></script>
<script src="./libraries/RGraph.pie.js" ></script>
</head>
<body background="../transparent.png">
<canvas id="cvs" >[No canvas support]</canvas>
<script>
function CreateGradient (obj, color)
return RGraph.RadialGradient(obj, 200, 150, 95, 200, 150, 125, color, color)
function isCanvasSupported()
var test_canvas = document.createElement("canvas");
var canvascheck=(test_canvas.getContext) ? true : false ;
return canvascheck;
window.onload = function ()
if(isCanvasSupported)
DrawPieChart();
else
document.write("hheheheheh");
function DrawPieChart ()
var canvas = document.getElementById('cvs');
var ctx = canvas.getContext('2d');
var pie = new RGraph.Pie('cvs', [2,3,6,7,82]);
pie.Set('chart.colors', [
CreateGradient(pie, '#580600'),
CreateGradient(pie, '#AEAEAE'),
CreateGradient(pie, '#860100'),
CreateGradient(pie, '#C7C7C7'),
CreateGradient(pie, '#A70000')
]);
pie.Set('chart.labels.sticks', true);
pie.Set('chart.labels.sticks.length', 5);
pie.Set('chart.tooltips', ['Autres',
'Italie',
'Royaume-Uni',
'Espagne',
'France']);
pie.Set('chart.labels', ['2%','3%','6%','7%','82%']);
pie.Set('chart.radius', 150);
pie.Set('chart.shadow', true);
pie.Set('chart.shadow.offsetx', 0);
pie.Set('chart.shadow.offsety', 0);
pie.Set('chart.shadow.blur', 25);
pie.Draw();
</script>
</body>
</html>
这是一个片段的代码：
@Override
public void onActivityCreated(Bundle savedInstanceState)
mWebView = (WebView)getActivity().findViewById(R.id.group_fragment_one_webView);
mWebView.setFocusable(false);
mWebView.loadUrl("file:///android_asset/graphs/graph1.html");
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.getSettings().setDefaultZoom(ZoomDensity.FAR);
mWebView.getSettings().setDefaultFontSize(24);
mWebView.getSettings().setBuiltInZoomControls(false);
mWebView.setBackgroundColor(0);
mWebView.setHorizontalScrollBarEnabled(false);
mWebView.setVerticalScrollBarEnabled(false);
mWebView.getSettings().setSupportZoom(false);
mWebView.getSettings().setRenderPriority(RenderPriority.HIGH);
String TAG = "HTML 5";
WebSettings ws = mWebView.getSettings();
ws.setJavaScriptEnabled(true);
ws.setAllowFileAccess(true);
if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.ECLAIR)
try
Method m1 = WebSettings.class.getMethod("setDomStorageEnabled", new Class[]Boolean.TYPE);
m1.invoke(ws, Boolean.TRUE);
Method m2 = WebSettings.class.getMethod("setDatabaseEnabled", new Class[]Boolean.TYPE);
m2.invoke(ws, Boolean.TRUE);
Method m3 = WebSettings.class.getMethod("setDatabasePath", new Class[]String.class);
m3.invoke(ws, "/data/data/" + getActivity().getApplicationContext().getPackageName() + "/databases/");
Method m4 = WebSettings.class.getMethod("setAppCacheMaxSize", new Class[]Long.TYPE);
m4.invoke(ws, 1024*1024*8);
Method m5 = WebSettings.class.getMethod("setAppCachePath", new Class[]String.class);
m5.invoke(ws, "/data/data/" + getActivity().getApplicationContext().getPackageName() + "/cache/");
Method m6 = WebSettings.class.getMethod("setAppCacheEnabled", new Class[]Boolean.TYPE);
m6.invoke(ws, Boolean.TRUE);
Log.d(TAG, "Enabled HTML5-Features");
catch (NoSuchMethodException e)
Log.e(TAG, "Reflection fail", e);
catch (InvocationTargetException e)
Log.e(TAG, "Reflection fail", e);
catch (IllegalAccessException e)
Log.e(TAG, "Reflection fail", e);
mTextView1 = (TextView)getActivity().findViewById(R.id.group_fragment_one_textview1);
mTextView1.setText(getActivity().getResources().getString(R.string.group_fragment_one_text1));
Spannable spanSize = new SpannableString(mTextView1.getText());
spanSize.setSpan(new RelativeSizeSpan(2.0f),
0,
mTextView1.getText().toString().indexOf("millions"),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
mTextView1.setText(spanSize);
Spannable colorSpan = new SpannableString(mTextView1.getText());
colorSpan.setSpan(new ForegroundColorSpan(getActivity().getResources().getColor(R.color.red_ribbon)),
0,
mTextView1.getText().toString().indexOf("millions"),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
mTextView1.setText(colorSpan);
mTextView1.setTypeface(Utils.getTextFont(getActivity().getApplicationContext()));
mTextView2 = (TextView)getActivity().findViewById(R.id.group_fragment_one_textview2);
mTextView2.setText(getActivity().getResources().getString(R.string.group_fragment_one_text2));
spanSize = new SpannableString(mTextView2.getText());
spanSize.setSpan(new RelativeSizeSpan(2.0f),
0,
mTextView2.getText().toString().indexOf("du chiffre"),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
mTextView2.setText(spanSize);
colorSpan = new SpannableString(mTextView2.getText());
colorSpan.setSpan(new ForegroundColorSpan(getActivity().getResources().getColor(R.color.red_ribbon)),
0,
mTextView2.getText().toString().indexOf("du chiffre"),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
mTextView2.setText(colorSpan);
mTextView2.setTypeface(Utils.getTextFont(getActivity().getApplicationContext()));
super.onActivityCreated(savedInstanceState);
它在模拟器和 Eclipse 浏览器上运行良好......但是当我想在智能手机上看到它时，我遇到了 Canvas 的错误。有时图表会正确显示，有时会显示“无画布支持”。在 ViewPager 中，只有片段 n、片段 n-1 和 n+1 被同时实例化。当用户在另一个片段上滚动时，会实例化其他片段。因此，每次用户滚动时，都会加载一个 HTML。有时画布受支持，有时不支持...
我试图在 javascript 中获得对画布的支持，但它总是返回支持画布，而事实并非如此......
有什么想法吗？
【问题讨论】：
【参考方案1】：尝试在onResume()方法上加载webview：
@Override
public void onResume()
mWebView.loadUrl("file:///android_asset/graphs/graph1.html");
super.onResume();
【讨论】：
也为我工作，我还清除了onPause()中的缓存以上是关于HTML5 Canvas 支持和 Android Webview的主要内容，如果未能解决你的问题，请参考以下文章