WebView从数据库异步加载图像 [英] WebView load images asynchronously from Database

问题描述

现在我可以做的只是替换 abc .jpg 部分< img src =abc.jpg> 由 data：image / jpg; base64 ，img_base64_string> ，但这必须在HTML get被呈现之前完成。我想尽快显示HTML页面，然后加载图片。

• 如何触发加载事件以加载图片

创建一个ParcelFileDescriptor.createPipe（）通过流复制数据库文件到WebView。

LocalImageContentProvider.java

  public class LocalImageContentProvider extends ContentProvider {
 
 private static final String AUTHORITY =com。 example.local.provider; 
 public static final Uri CONTENT_URI = Uri.parse（content：//+ AUTHORITY +/ image）; 
 
 @Override 
 public ParcelFileDescriptor openFile（Uri uri，String mode）{
 String filename = uri.getLastPathSegment（）; 
 
 // http://developer.android.com/reference/android/os/ParcelFileDescriptor.html#createPipe%28%29 
 // [0]是读者，[1] ]是作者
 ParcelFileDescriptor [] pipe = null; 
 
 try {
 pipe = ParcelFileDescriptor.createPipe（）; 
 
 //通过管道将DB文件复制到WebView 
 new Thread（new PipeRunnable（
 getInputStreamFromDbFile（filename），
 new AutoCloseOutputStream（pipe [1]）） 
 .start（）; 
 
} catch（IOException e）{
 e.printStackTrace（）; 
} 
 
 return（pipe [0]）; 
} 
} 
  

Manifest.xml

 <？xml version =1.0encoding =utf-8？> 
< manifest xmlns：android =http://schemas.android.com/apk/res/android> 
 
< uses-sdk android：minSdkVersion =9android：targetSdkVersion =19/> 
 
< application> 
 
<！ - 'activity  - > 
 
< provider android：exported =false
 android：name =。provider.LocalImageContentProvider
 android：authorities =com.example.local.provider
 /> 
 
< / application> 
 
< / manifest> 
  

要在WebView中加载图像，请使用ContentProvider URI +/image.jpg：

< img src =content：//com.example.local.provider/image/29.jpg>< / img> p>

I would like to load images referenced in HTML asynchronously from my local Database.

Right now all I can do is to replace the abc.jpg part of <img src="abc.jpg"> by data:image/jpg;base64, img_base64_string>, but this has to be done before the HTML get's rendered. I would like to show the HTML page as fast as possible and then load the images.

• How to trigger a loading event to load an image from the DB?
• How to correctly set the loaded image in HTML without converting it to base64?

解决方案

The trick is to create a ParcelFileDescriptor.createPipe() to copy the database file through streams to the WebView.

LocalImageContentProvider.java

public class LocalImageContentProvider extends ContentProvider {

    private static final String AUTHORITY = "com.example.local.provider";
    public static final Uri CONTENT_URI = Uri.parse("content://"+ AUTHORITY +"/image");

    @Override
    public ParcelFileDescriptor openFile(Uri uri, String mode) {
        String filename = uri.getLastPathSegment();

        // http://developer.android.com/reference/android/os/ParcelFileDescriptor.html#createPipe%28%29     
        // [0] is the reader, [1] is the writer
        ParcelFileDescriptor[] pipe = null;

        try {
            pipe = ParcelFileDescriptor.createPipe();

            // copy DB file through pipe to WebView
            new Thread(new PipeRunnable(
                    getInputStreamFromDbFile(filename),
                    new AutoCloseOutputStream(pipe[1])) )
            .start();

        } catch (IOException e) {
            e.printStackTrace();
        }

        return (pipe[0]);
    }
}

Manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" >

    <uses-sdk android:minSdkVersion="9" android:targetSdkVersion="19"/>

    <application>

        <!-- 'activity -->

        <provider android:exported="false"
            android:name=".provider.LocalImageContentProvider"
            android:authorities="com.example.local.provider"
        />

    </application>

</manifest>

To load images in the WebView use the ContentProvider URI + "/image.jpg":
<img src="content://com.example.local.provider/image/29.jpg"></img>

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