多媒体——图片——图像解码器ImageDecoder

比眉伴天荒 2024-04-03 09:06 64阅读 0赞

图像解码器ImageDecoder

早期的Android只支持三种图像格式：JPEG、PNG和GIF，而且图像视图仅能显示动图的初始画面，无法直接播放动画效果。

时代呼唤技术更先进的图像压缩算法，谷歌推出了WebP格式，苹果推出了HEIF格式。WebP与HEIF都具备了下列特性：

(1)支持透明背景；(JPEG不支持透明背景)(2)支持动画效果；(JPEG和PNG不支持动画效果)(3)支持有损压缩；(PNG和GIF不支持有损压缩，因此它们的图片体积较大)

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布局：

![cdee1b63402c5874472a3dfac44c9ee2.png][]

item\_select.xml

![a12566a7ec9db0488dbf1c449c936e29.png][]

代码：

package com.example.myapplication;
    
    import androidx.annotation.RequiresApi;
    import androidx.appcompat.app.AppCompatActivity;
    import android.graphics.ImageDecoder;
    import android.graphics.ImageDecoder.OnHeaderDecodedListener;
    import android.graphics.drawable.Animatable;
    import android.graphics.drawable.Drawable;
    import android.os.Build;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.ImageView;
    import android.widget.Spinner;
    import android.widget.TextView;
    import java.io.IOException;
    import java.io.InputStream;
    import java.nio.ByteBuffer;
    
    @RequiresApi(api = Build.VERSION_CODES.P)
    public class MainActivity extends AppCompatActivity
    {
    
        private TextView tv_info; // 声明一个文本视图对象
        private ImageView iv_pic; // 声明一个图像视图对象
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
            tv_info = findViewById(R.id.tv_info);
            iv_pic = findViewById(R.id.iv_pic);
    
            initTypeSpinner(); // 初始化图像类型下拉框
        }
    
        private String[] typeArray = {"直接显示GIF", "直接显示WebP", "显示GIF动图", "显示WebP动图", "显示HEIF图片"};
    
    
        // 初始化图像类型下拉框
        private void initTypeSpinner()
        {
    
            ArrayAdapter<String> typeAdapter = new ArrayAdapter<String>(this, R.layout.item_select, typeArray);
    
            Spinner sp_type = findViewById(R.id.sp_type);
    
            sp_type.setPrompt("请选择图像类型");
    
            sp_type.setAdapter(typeAdapter);
    
            sp_type.setOnItemSelectedListener(new MainActivity.ImageTypeListener());
    
            sp_type.setSelection(0);
        }
    
        class ImageTypeListener implements AdapterView.OnItemSelectedListener
        {
    
            public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3)
            {
    
                if (arg2 == 0)
                {
                    tv_info.setText("");
                    iv_pic.setImageResource(R.drawable.happy);
                }
                else if (arg2 == 1)
                {
                    tv_info.setText("");
                    iv_pic.setImageResource(R.drawable.world_cup_2014);
                }
                else if (arg2 == 2)
                {
                    showImage(R.drawable.happy); // 显示gif和webp图片
                }
                else if (arg2 == 3)
                {
                    showImage(R.drawable.world_cup_2014); // 显示gif和webp图片
                }
                else if (arg2 == 4)
                {
                    showHeic(R.raw.lotus); // 显示Heif图片(扩展名为heif或者heic)
                }
            }
    
            public void onNothingSelected(AdapterView<?> arg0) {}
        }
    
    
    
    
        // 显示Heif图片(扩展名为heif或者heic)
        private void showHeic(int imageId)
        {
    
            try (InputStream is = getResources().openRawResource(imageId)) // 从资源文件中获取输入流对象
            {
                byte[] bytes = new byte[is.available()]; // 创建临时存放的字节数组
    
                is.read(bytes); // 从输入流中读取字节数组
    
    
                ImageDecoder.Source source = ImageDecoder.createSource(ByteBuffer.wrap(bytes)); // 利用Android 9.0新增的ImageDecoder读取图片
    
                showImageSource(source); // 显示指定来源的图像
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    
    
    
    
        // 显示gif和webp图片
    
        private void showImage(int imageId)
        {
            try
            {
                // 利用Android 9.0新增的ImageDecoder读取图片
                ImageDecoder.Source source = ImageDecoder.createSource(getResources(), imageId);
    
                showImageSource(source); // 显示指定来源的图像
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    
    
    
    
        // 显示指定来源的图像
        private void showImageSource(ImageDecoder.Source source) throws IOException
        {
            // 从数据源解码得到图形信息
            Drawable drawable = ImageDecoder.decodeDrawable(source, new OnHeaderDecodedListener() {
                @Override
                public void onHeaderDecoded(ImageDecoder decoder, ImageDecoder.ImageInfo info, ImageDecoder.Source source) {
                    // 获取图像信息的媒体类型与是否动图
                    String desc = String.format("该图片类型为%s，它%s动图",
                            info.getMimeType(), info.isAnimated()?"是":"不是");
                    tv_info.setText(desc);
                }
            });
    
            iv_pic.setImageDrawable(drawable); // 设置图像视图的图形对象
    
            if (drawable instanceof Animatable)  // 如果是动画图形，则开始播放动画
            {
                ((Animatable) iv_pic.getDrawable()).start();
            }
        }
    
    }

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[ab3c96460af01538644bfdc8ef92ce27.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/d6a6417c668f4aa0bb0ddad69e668440.png
[d7aa06ab396d05db9c7a0baad2718ec9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/b2ada974fa0649a4aa5b721ae3707d5c.png
[cdee1b63402c5874472a3dfac44c9ee2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/2548a50c81cf41d08fc72d4356ae5d61.png
[a12566a7ec9db0488dbf1c449c936e29.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/437a5bedf5334bab8f4acbdcaaa99678.png
[84c0f270a8cc7df9fa4b8ad31e512dca.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/bae96176a144455a87e0afeba00e1d5d.png
[79a6e5a0873e7ff488bb768cae352fcd.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/32f10c60c49d40688ed00b1a163df048.png
[954f307917da49b9c04b9af8bb25c707.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/44ee702360e6481094028de6bd1e5d4d.png
[03802b80726b901949c7e5b8fea4200f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/345b4ffdcf284b3aaa98f4aabfc0109c.png
[b3dbee18ad58f448ba693e12e5420e82.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/7274e927f00e41f9aab97c5705de8c49.png
[d2e778b2480d60ecc612f2c0dd4fef0e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/414fc92bb85d468fb4981b2bffa80f4e.png
[916f5a73d3311648490d73f694aaeb90.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/1a8c4e7872954e1b8d6e80804202a3d1.png