【HarmonyOS】【JAVA UI】鸿蒙怎么对图片编码为 base64 和 base64 解码为 PixelMap，并显示在控件上

在 HarmonyOS 中对图片的解码和编码是常见的操作，在 HarmonyOS 怎么进行编码和解码呢？今天写一个 demo 进行实现该功能实现，我们从以下几个步骤进行讲解该功能

1. 准备环节

2. 图片编码为 Base64 字符串

3. Base64 解码为 PixelMap，并显示在 Image 控件上

第一步准备环节

1.1 准备一张图片放在 resources/rawfile 文件夹下，图片如下

1.2 新建 ImageAbilitySlice java 类和 xml 布局， xml 布局如下

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:height="match_parent"
    ohos:width="match_parent"
    ohos:orientation="vertical">
    <Text
        ohos:height="100vp"
        ohos:width="match_parent"
        ohos:background_element="#ffffff"
        ohos:text="图片编码"
        ohos:text_size="20vp"
        ohos:text_alignment="center"
        ohos:id="$+id:textRead"/>
    <Text
        ohos:id="$+id:getmPixelMapAndShowImage"
        ohos:height="100vp"
        ohos:width="match_parent"
        ohos:text="图片解码并显示"
        ohos:background_element="#ed6262"
        ohos:text_size="20vp"
        ohos:text_alignment="center"/>
 
    <Image
        ohos:height="match_parent"
        ohos:width="match_parent"
        ohos:id="$+id:ShowImage"/>
 
</DirectionalLayout>

XML 效果图如下

第二步图片编码为 Base64 字符串

2.1 这边我们参考资料是 Base64 的基本用法，来写一个工具类，代码如下

package com.harmony.alliance.mydemo.utils;
 
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Base64;
 
public class ImageUtils {
 
    /**
     * 将图片转换成Base64编码的字符串
     */
    public static String imageToBase64(String path) {
        if(path==null||path.equals("")) {
            return null;
        }
        InputStream is = null;
        byte[] data = null;
        String result = null;
        try {
            is = new FileInputStream(path);
            //创建一个字符流大小的数组。
            data = new byte[is.available()];
            //写入数组
            is.read(data);
            //用默认的编码格式进行编码
            result = Base64.getEncoder().encodeToString(data);
        }catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(null !=is) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
 
        }
        return result;
    }
 
    /**
     * 将图片转换成Base64编码的字符串
     */
    public static String imageInputStreamToBase64(  InputStream is) {
        if(is==null) {
            return null;
        }
        byte[] data = null;
        String result = null;
        try {
            //创建一个字符流大小的数组。
            data = new byte[is.available()];
            //写入数组
            is.read(data);
            //用默认的编码格式进行编码
            result = Base64.getEncoder().encodeToString(data);
        }catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(null !=is){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
 
        }
        return result;
    }
}

2.2 实现图片编码的代码如下

textRead.setClickedListener(new Component.ClickedListener() {
    @Override
    public void onClick(Component component) {
        try {
            String filePath = String.format(Locale.ROOT, "assets/entry/resources/rawfile/%s", "icon.png");
            InputStream is = this.getClass().getClassLoader().getResourceAsStream(filePath);
            //Todo 得到base64字符串
            ImageData="data:image/png;base64,"+ ImageUtils.imageInputStreamToBase64(is);
            HiLogUtils.PrintLog(ImageData);
        }catch (Exception e) {
            e.printStackTrace();
        }
 
    }
});

效果图如下

第三步将 Base64 解码为 mPixelMap 并显示在 Image 控件上

3.1 我们这里使用如下 Base64.getDecoder().decode 和 ImageSource、SourceOptions 的相关技术，代码如下

findComponentById(ResourceTable.Id_getmPixelMapAndShowImage).setClickedListener(new Component.ClickedListener() {
    @Override
    public void onClick(Component component) {
    String Base64Data=  ImageData.replace("data:image/png;base64,","");
    //todo base64字符串得到字节
    byte[] base64byte=     java.util.Base64.getDecoder().decode(Base64Data);
    ImageSource.SourceOptions srcOpts = new ImageSource.SourceOptions();
    srcOpts.formatHint = "image/png";
    ImageSource imageSource = ImageSource.create(base64byte, srcOpts);
    // 设置图片参数
    ImageSource.DecodingOptions decodingOptions = new ImageSource.DecodingOptions();
    PixelMap mPixelMap = imageSource.createPixelmap(decodingOptions);
    ShowImage.setPixelMap(mPixelMap);
    }
});

效果图如下

整体代码如下

package com.harmony.alliance.mydemo.slice;
 
import com.harmony.alliance.mydemo.ResourceTable;
import com.harmony.alliance.mydemo.utils.ImageUtils;
import ohos.aafwk.ability.AbilitySlice;
import ohos.aafwk.content.Intent;
import ohos.agp.components.Component;
import ohos.agp.components.Image;
import ohos.agp.components.Text;
import ohos.global.resource.RawFileEntry;
import ohos.global.resource.Resource;
import ohos.media.image.ImageSource;
import ohos.media.image.PixelMap;
 
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Base64;
import java.util.Locale;
 
public class ImageAbilitySlice  extends AbilitySlice {
    Image ShowImage;
    private   String ImageData;
    @Override
    protected void onStart(Intent intent) {
        super.onStart(intent);
        setUIContent(ResourceTable.Layout_iamge_ability_slice);
        Text textRead= (Text) findComponentById(ResourceTable.Id_textRead);
        ShowImage= (Image) findComponentById(ResourceTable.Id_ShowImage);
        textRead.setClickedListener(new Component.ClickedListener() {
            @Override
            public void onClick(Component component) {
                try {
                    String filePath = String.format(Locale.ROOT, "assets/entry/resources/rawfile/%s", "icon.png");
                    InputStream is = this.getClass().getClassLoader().getResourceAsStream(filePath);
                    //Todo 得到base64字符串
                    ImageData="data:image/png;base64,"+       ImageUtils.imageInputStreamToBase64(is);
                    HiLogUtils.PrintLog(ImageData);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
 
        findComponentById(ResourceTable.Id_getmPixelMapAndShowImage).setClickedListener(new Component.ClickedListener() {
            @Override
            public void onClick(Component component) {
                String Base64Data=  ImageData.replace("data:image/png;base64,","");
                //todo base64字符串得到字节
                byte[] base64byte=     java.util.Base64.getDecoder().decode(Base64Data);
                ImageSource.SourceOptions srcOpts = new ImageSource.SourceOptions();
                srcOpts.formatHint = "image/png";
                ImageSource imageSource = ImageSource.create(base64byte, srcOpts);
                // 设置图片参数
                ImageSource.DecodingOptions decodingOptions = new ImageSource.DecodingOptions();
                PixelMap mPixelMap =      imageSource.createPixelmap(decodingOptions);
                ShowImage.setPixelMap(mPixelMap);
            }
        });
    }
}

效果如下