Android自定义视图中图片的处理

//把一个Bitmap对象包装成BitmapDrawable对象
BitmapDrawable drawable = new BitmapDrawable (bitmap) ;

//获取BitmapDrawable所包装的Bitmap 对象
Bitmap bitmap = drawable.getBitmap();

public class Test4Activity extends Activity {
    String[] images = null;
    AssetManager assets = null;
    int currentImg = 0;
    private ImageView image;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test4_acitvity);
        image = findViewById(R.id.test4_iv);
        Button next = findViewById(R.id.test4_bt_next);
        try {
            assets = getAssets();
            //获取assets目录目录下的所有文件
            images =assets.list("");
        } catch (ioException e) {
            e.printStackTrace();
        }
        //按钮事件
        next.setOnClickListener(view -> {
            //如果发生数组越界
            if(currentImg >= images.length){
                currentImg = 0;
            }
            //找到下一个图片文件
            while (!images[currentImg].endsWith(".png")&&!images[currentImg].endsWith(".jpg")
                    &&!images[currentImg].endsWith(".gif")){
                currentImg++;
                //如果已经发生了数组越界
                if(currentImg >= images.length){
                    currentImg = 0;
                }
            }
            InputStream assetFile = null;
            try {
                //打开指定资源对应的输入流
                assetFile = assets.open(images[currentImg++]);
            } catch (IOException e) {
                e.printStackTrace();
            }
            BitmapDrawable bitmapDrawable = (BitmapDrawable) image.getDrawable();
            //如果图片还未回收，先强制回收该图片
            if(bitmapDrawable != null&&!bitmapDrawable.getBitmap().isRecycled()){
                bitmapDrawable.getBitmap().recycle();
            }
            //改变ImageView显示图片
            //调用了BitmapFactory从指定输入流解析并创建Bitmap
            image.setImageBitmap(BitmapFactory.decodeStream(assetFile));
        });
    }
}

AssetManager assset= getAssets();  
InputStream is = assset.open("filename");

assetFile = assets.open(images[currentImg++]);

public class Test5Activity extends AppCompatActivity {
    //说白了只有api 28 之后的才进的来
    @RequiresApi(api = Build.VERSION_CODES.P)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test5);
        //获取对象
        TextView textView = findViewById(R.id.test5_tv);
        ImageView imageView = findViewById(R.id.test5_iv);
        //创建 imageDecoder.Source对象
            //第一步：
            ImageDecoder.Source source = ImageDecoder.createSource(getResources(),R.drawable.viewgif);
            try {
                //第二步：执行decodeDrawable()方法获取Drawable对象
                @SuppressLint({"WrongThread", "SetTextI18n"})
                Drawable drawable = ImageDecoder.decodeDrawable(source,(decoder, info, s) ->{
                    //通过 info 参数获取被解码图片的信息
                    textView.setText("图片的原始宽度："+info.getSize().getWidth()+
                            "\n"+"图片原始宽高"+info.getSize().getHeight());
                    //设置图片解码之后的缩放大小
                    decoder.setTargetSize(600,580);
                });
                imageView.setImageDrawable(drawable);
                //如果drawable 是AnimatedImageDrawable的实例，则执行动画
                if(drawable instanceof AnimatedImageDrawable){
                    ((AnimatedImageDrawable) drawable).start();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
}

//先用Lambda 表达式作为OnHeaderDecodeListener监听器
    Drawable drawable = ImageDecoder.decodeDrawable(source,(decoder, info, s) ->{
        //为ImageDecoder 设置 OnPartialImageListener 监听器（Lambda 表达式）
        decoder.setOnPartialImageListener(e->{
            ....
            //return true 表明即使不能完整地解码全部图片也返回Drawable或Bitmap
            return true;
        });
    });