小贝子编程

Android:如何在webview中渲染html而不显示webview



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。它几乎起作用了。问题是我似乎无法设置Webview的尺寸，因此HTML以我想要的尺寸呈现。我正在使用WebviewClient来拍摄WebviewContent的快照并将其转换为位图。

下面的代码只是用于测试，而不是我的最终意图。我根本不想显示内容，但这是对功能的测试，当用户点击打印按钮时，会填充一个图像。我想图像是380的宽度(高度可以尽可能高，是必要的)。图片非常小(87 x 144)。

下面的代码有两个问题:

  1. 第一次运行时，快照总是抛出一个异常，指示位图尺寸必须为>0

  2. 在第二次尝试(以及随后的尝试)时，产生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;

    进口androidx.appcompat.app.AppCompatActivity;

    进口android.graphics.Bitmap;进口android.graphics.Canvas;进口android.graphics.Paint;进口android.os.Bundle;进口android.view.View;进口android.webkit.WebView;进口android.webkit.WebViewClient;进口android.widget.Button;进口android.widget.ImageView;进口android.util.Log;

    进口java.io.BufferedReader;进口java.io.IOException;进口java.io.InputStreamReader;

    /* *

    • MainActivity

    */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_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
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_width="wrap_content"
android:layout_height="wrap_content"
android:text="Print" />
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/imgPreview"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</ScrollView>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

要解决问题(1)，调用WebView.Layout(…)而不是设置宽度和高度。

要解决问题(2)，WebView必须在Activities的onCreate(…)方法中创建。

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
//-----------------------------
}

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