Android：如何在webview中呈现html而不显示webview
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【中文标题】Android：如何在webview中呈现html而不显示webview【英文标题】：Android: How to render html in webview without displaying webview 【发布时间】：2021-10-20 14:46:06 【问题描述】：我想使用 Webview 呈现 html，但我不想显示内容。为此，我以编程方式创建一个 Webview 并加载 HTML。它几乎可以工作了。问题是我似乎无法设置 Webview 的尺寸，因此 HTML 以我想要的大小呈现。我正在使用 WebviewClient 拍摄 WebviewContent 的快照并将其转换为位图。
以下代码仅用于测试，并非我的最终意图。我根本不想显示内容，但这会测试功能，当用户点击打印按钮时会填充图像。我希望图像的宽度为 380（高度可以根据需要高）。图片非常小（87 x 144）。
我对以下代码有 2 个问题：
第一次运行时，快照总是抛出异常，指示位图尺寸必须> 0
在第二次尝试（以及后续尝试）时，生成的位图不是所需的尺寸。当然，缩放只会让情况变得更糟。
包 com.b2ps.htmlrender;
导入androidx.appcompat.app.AppCompatActivity；
导入 android.graphics.Bitmap; 导入android.graphics.Canvas； 导入android.graphics.Paint； 导入android.os.Bundle； 导入android.view.View； 导入 android.webkit.WebView； 导入 android.webkit.WebViewClient； 导入android.widget.Button； 导入android.widget.ImageView； 导入android.util.Log；
导入 java.io.BufferedReader; 导入 java.io.IOException； 导入 java.io.InputStreamReader;
/**
主要活动*/ 公共类 MainActivity 扩展 AppCompatActivity
private static final String TAG = "USDK";
private ImageView ImagePreview = null;
private WebView mReceiptView = null;
private WebViewClient mWebviewClient = null;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
WebView.enableSlowWholeDocumentDraw();
Button printBtn = ( Button )findViewById( R.id.btnPrint );
printBtn.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
onPrintClicked();
);
ImagePreview = ( ImageView )findViewById( R.id.imgPreview );
private void onPrintClicked()
print();
private void print()
mReceiptView = new WebView( this );
mWebviewClient = new SnapshotWebviewClient( this );
mReceiptView.setWebViewClient( mWebviewClient );
mReceiptView.setMinimumWidth( 380 );
mReceiptView.setMinimumHeight( 720 );
String receiptHtml = getHtml();
mReceiptView.loadData( receiptHtml, "text/html; charset=utf-8", "UTF-8" );
protected String getHtml()
StringBuilder htmlStr = new StringBuilder();
BufferedReader reader = null;
try
reader = new BufferedReader( new InputStreamReader( this.getAssets().open("Receipt2.html" ) ) );
// do reading, usually loop until end of file reading
String mLine;
while ((mLine = reader.readLine()) != null)
//process line
htmlStr.append( mLine );
htmlStr.append( "\n" );
catch (IOException e)
//log the exception
Log.e( TAG, "IO exception", e);
finally
if (reader != null)
try
reader.close();
catch (IOException e)
//log the exception
Log.e( TAG, "error closing stream", e );
return htmlStr.toString();
//---------------------------------------------------------------------------------------------
// #region SnapshotWebviewClient
/**
* SnapshotWeviewClient
*/
private static class SnapshotWebviewClient extends WebViewClient
private static final String TAG = "USDK";
private MainActivity mMainActivity;
public SnapshotWebviewClient( MainActivity activity )
mMainActivity = activity;
@Override
public void onPageFinished(WebView view, String url)
// FYI anyone wanting to do this right, use webView.ScrollView.ContentSize.Height then
// set the Frame of the webview. Works perfect!
Log.i( TAG, "SnapshotWebviewClient.onPageFinished" );
super.onPageFinished( view, url );
try
// Thread.sleep( 25 );
// Bitmap bitmap = Bitmap.CreateBitmap( view.MeasuredWidth, view.ContentHeight, Bitmap.Config.Argb8888 );
// Canvas canvas = new Canvas( bitmap );
// Paint paint = new Paint();
// int iHeight = bitmap.Height;
// canvas.DrawBitmap( bitmap, 0, iHeight, paint );
// view.Draw( canvas );
Bitmap bitmap = screenshot( view );
// bitmap = scaleToReceipt( bitmap, 380 );
Log.i( TAG, String.format( "Bitmap size: w(%d), h(%d)", bitmap.getWidth(), bitmap.getHeight() ) );
mMainActivity.ImagePreview.setImageBitmap( bitmap );
// save bitmap to file
java.io.File externalPath = view.getContext().getExternalFilesDir( null );
java.io.File filePath = new java.io.File( externalPath, "Receipt.png" );
java.io.FileOutputStream stream = new java.io.FileOutputStream( filePath );
bitmap.compress( Bitmap.CompressFormat.PNG, 100, stream );
stream.close();
Log.i( TAG, "WebViewClient.PrintToBitmap" );
catch ( Exception printErr )
Log.e( TAG, "PrintWebView: "+printErr.toString(), printErr );
private Bitmap screenshot(android.webkit.WebView webView )
webView.measure( View.MeasureSpec.makeMeasureSpec( 0, View.MeasureSpec.UNSPECIFIED ),
android.view.View.MeasureSpec.makeMeasureSpec( 0, View.MeasureSpec.UNSPECIFIED ) );
Log.i( TAG, String.format( "webView dimensions1: w(%d), h(%d)", webView.getMeasuredWidth(), webView.getMeasuredHeight() ) );
webView.layout( 0, 0, webView.getMeasuredWidth(), webView.getMeasuredHeight() );
Log.i( TAG, String.format( "webView dimensions2: w(%d), h(%d)", webView.getMeasuredWidth(), webView.getMeasuredHeight() ) );
webView.setDrawingCacheEnabled( true );
webView.buildDrawingCache();
Bitmap bitmap = Bitmap.createBitmap( webView.getMeasuredWidth(), webView.getMeasuredHeight(), Bitmap.Config.ARGB_8888 );
Log.i( TAG, String.format( "HtmlBmp: w(%d), h(%d)", bitmap.getWidth(), bitmap.getHeight() ) );
Canvas canvas = new Canvas( bitmap );
Paint paint = new Paint();
int iHeight = bitmap.getHeight();
canvas.drawBitmap( bitmap, 0, iHeight, paint );
webView.draw( canvas );
return bitmap;
private Bitmap scaleToReceipt( Bitmap bmp, int printWidth )
double scale = (( double )(printWidth - 1) / ( double )bmp.getWidth());
int w = ( int )(bmp.getWidth() * scale);
int h = ( int )(bmp.getHeight() * scale);
Log.i( TAG, String.format( "Scale Bmp: W(%d), H(%d)", w, h ) );
return Bitmap.createScaledBitmap( bmp, w, h, true );
// #endregion SnapshowWebviewClient
//---------------------------------------------------------------------------------------------
这是布局 XML
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
tools:context=".MainActivity">
<LinearLayout
android:layout_
android:layout_
android:orientation="vertical"
android:gravity="center"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" >
<Button
android:id="@+id/btnPrint"
android:layout_
android:layout_
android:text="Print" />
<ScrollView
android:layout_
android:layout_ >
<ImageView
android:id="@+id/imgPreview"
android:layout_
android:layout_ />
</ScrollView>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
【问题讨论】：
所以我解决了我的一个问题。我现在可以得到一个缩放到正确大小的位图。而不是： mReceiptView.setMinimumWidth( 380 ); mReceiptView.setMinimumHeight(720);使用：mReceiptView.layout(0, 0, 380, 720);当其他问题解决时，我会设置答案。在此调用的第一次迭代中，我仍然得到 0 x 0 的位图大小。并且间歇性地。当我调试并设置断点时，它发生的较少。因此，似乎存在一些时间问题。但我在 GUI 线程上做所有事情。 【参考方案1】：要解决问题 (1)，请调用 WebView.Layout(...) 而不是设置宽度和高度。
要解决问题 (2)，必须在活动的 onCreate(...) 方法中创建 WebView。
见下文：
/**
* MainActivity
*/
public class MainActivity extends AppCompatActivity
private static final String TAG = "USDK";
private ImageView ImagePreview = null;
private WebView mReceiptView = null;
private WebViewClient mWebviewClient = null;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
WebView.enableSlowWholeDocumentDraw();
Button printBtn = (Button) findViewById(R.id.btnPrint);
printBtn.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
onPrintClicked();
);
ImagePreview = (ImageView) findViewById(R.id.imgPreview);
mReceiptView = new WebView( this.getApplicationContext() );
mWebViewClientClient = new ReceiptWebViewClient();
mReceiptView.layout( 0, 0, 380, 720 );
mReceiptView.setWebViewClient( mWebViewClientClient );
mReceiptView.loadData("<html></html>", "text/html; charset=utf-8", "UTF-8" );
private void onPrintClicked()
print();
private void print()
String receiptHtml = getHtml();
mReceiptView.loadData(receiptHtml, "text/html; charset=utf-8", "UTF-8");
protected String getHtml()
StringBuilder htmlStr = new StringBuilder();
BufferedReader reader = null;
try
reader = new BufferedReader(new InputStreamReader(this.getAssets().open("Receipt2.html")));
// do reading, usually loop until end of file reading
String mLine;
while ((mLine = reader.readLine()) != null)
//process line
htmlStr.append(mLine);
htmlStr.append("\n");
catch (IOException e)
//log the exception
Log.e(TAG, "IO exception", e);
finally
if (reader != null)
try
reader.close();
catch (IOException e)
//log the exception
Log.e(TAG, "error closing stream", e);
return htmlStr.toString();
//---------------------------------------------------------------------------------------------
// #region SnapshotWebviewClient
/**
* SnapshotWeviewClient
*/
private static class SnapshotWebviewClient extends WebViewClient
private static final String TAG = "USDK";
private MainActivity mMainActivity;
public SnapshotWebviewClient(MainActivity activity)
mMainActivity = activity;
@Override
public void onPageFinished(WebView view, String url)
// FYI anyone wanting to do this right, use webView.ScrollView.ContentSize.Height then
// set the Frame of the webview. Works perfect!
Log.i(TAG, "SnapshotWebviewClient.onPageFinished");
super.onPageFinished(view, url);
if ( url.compareTo( "data:text/html; charset=utf-8,<html></html>" ) == 0 )
return;
try
Bitmap bitmap = screenshot(view);
// bitmap = scaleToReceipt( bitmap, 380 );
Log.i(TAG, String.format("Bitmap size: w(%d), h(%d)", bitmap.getWidth(), bitmap.getHeight()));
mMainActivity.ImagePreview.setImageBitmap(bitmap);
// save bitmap to file
java.io.File externalPath = view.getContext().getExternalFilesDir(null);
java.io.File filePath = new java.io.File(externalPath, "Receipt.png");
java.io.FileOutputStream stream = new java.io.FileOutputStream(filePath);
bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
stream.close();
Log.i(TAG, "WebViewClient.PrintToBitmap");
catch (Exception printErr)
Log.e(TAG, "PrintWebView: " + printErr.toString(), printErr);
private Bitmap screenshot(android.webkit.WebView webView)
webView.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
android.view.View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
Log.i(TAG, String.format("webView dimensions1: w(%d), h(%d)", webView.getMeasuredWidth(), webView.getMeasuredHeight()));
webView.layout(0, 0, webView.getMeasuredWidth(), webView.getMeasuredHeight());
Log.i(TAG, String.format("webView dimensions2: w(%d), h(%d)", webView.getMeasuredWidth(), webView.getMeasuredHeight()));
webView.setDrawingCacheEnabled(true);
webView.buildDrawingCache();
Bitmap bitmap = Bitmap.createBitmap(webView.getMeasuredWidth(), webView.getMeasuredHeight(), Bitmap.Config.ARGB_8888);
Log.i(TAG, String.format("HtmlBmp: w(%d), h(%d)", bitmap.getWidth(), bitmap.getHeight()));
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
int iHeight = bitmap.getHeight();
canvas.drawBitmap(bitmap, 0, iHeight, paint);
webView.draw(canvas);
return bitmap;
private Bitmap scaleToReceipt(Bitmap bmp, int printWidth)
double scale = ((double) (printWidth - 1) / (double) bmp.getWidth());
int w = (int) (bmp.getWidth() * scale);
int h = (int) (bmp.getHeight() * scale);
Log.i(TAG, String.format("Scale Bmp: W(%d), H(%d)", w, h));
return Bitmap.createScaledBitmap(bmp, w, h, true);
// #endregion SnapshowWebviewClient
//-----------------------------
【讨论】：
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