在Android中显示APNG动图

String url = "http://xxx.png";
imageView.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        ApngDrawable apngDrawable = ApngDrawable.getFromView(v);
        if (apngDrawable == null) return;
        if (apngDrawable.isRunning()) {
            apngDrawable.stop();  // 停止播放动画
        } else {
            apngDrawable.setNumPlays(3); // 动画循环次数
            apngDrawable.start(); // 开始播放动画
        }
    }
});

ApngImageLoader.getInstance().displayImage(url, imageView);

// 文件路径：com/github/sahasbhop/apngview/ApngDrawable.java
private void prepare() {
 	// 1. 构造File对象
	String imagePath = getImagePathFromUri();
	if (imagePath == null) return;
	baseFile = new File(imagePath);
	if (!baseFile.exists()) return;
	// 2. 读取一个APNG文件并尝试将其拆分帧
	ApngExtractFrames.process(baseFile);
	// 3. 读取APNG文件信息
	readApngInformation(baseFile);
	isPrepared = true;
}

// 文件路径：com/github/sahasbhop/apngview/assist/ApngExtractFrames.java
public static int process(final File orig) {
	PngReaderBuffered pngr = new PngReaderBuffered(orig); // 这里应该是在读取了这个图片
	pngr.end();
	return pngr.frameIndex + 1;
}

// 文件路径：com/github/sahasbhop/apngview/assist/ApngExtractFrames.java
protected void postProcessChunk(ChunkReader chunkR) {
	//......
    try {
        String id = chunkR.getChunkRaw().id;
        PngChunk lastChunk = chunksList.getChunks().get(chunksList.getChunks().size() - 1);
        if (id.equals(PngChunkFCTL.ID)) { // FCTL代表，每一帧开头
            frameIndex++;
            frameInfo = ((PngChunkFCTL) lastChunk).getEquivImageInfo();
            startNewFile(); // 开始新建一个文件，进行输入
        }
        if (id.equals(PngChunkFDAT.ID) || id.equals(PngChunkIDAT.ID)) { // 图像数据块
            // 忽略这里的处理细节....
        }
        if (id.equals(PngChunkIEND.ID)) { // 这一帧结束
            if (fo != null)
                endFile(); // 结束这个文件输入，对应startNewFile方法
        }
    } catch (Exception e) {
        throw new PngjException(e);
    }
}

// 文件路径：com/github/sahasbhop/apngview/ApngDrawable.java
private void readApngInformation(File baseFile) {
	PngReaderApng reader = new PngReaderApng(baseFile); // 又读取了一次文件，这里和步骤二或许可以合并优化下
	reader.end();

	List<PngChunk> pngChunks = reader.getChunksList().getChunks(); // 拿到图片所有数据块
	PngChunk chunk;

	for (int i = 0; i < pngChunks.size(); i++) {
		chunk = pngChunks.get(i);
		if (chunk instanceof PngChunkACTL) {
			numFrames = ((PngChunkACTL) chunk).getNumFrames();  //获取总帧数
			if (numPlays > 0) {
				//......
			} else {
				numPlays = ((PngChunkACTL) chunk).getNumPlays(); // 获取循环播次数
			}
		} else if (chunk instanceof PngChunkFCTL) {
			fctlArrayList.add((PngChunkFCTL) chunk); // 收集帧动画控制的数据块
		}
	}
}

// 文件路径：com/github/sahasbhop/apngview/ApngDrawable.java
	public void start() {
		if (!isRunning()) {
			isRunning = true;
			currentFrame = 0;
			if (!isPrepared) {
				prepare();
			}
            if (isPrepared) {
                run();
				if (apngListener != null) apngListener.onAnimationStart(this);
            } else {
                stop();
            }
		}
	}

public void run() {
	if (showLastFrameOnStop && numPlays > 0 && currentLoop >= numPlays) {
		stop(); // 轮播次数用完且到最后一帧了就停止播放了
		return;
	}

	if (currentFrame < 0) {
		currentFrame = 0;
	} else if (currentFrame > fctlArrayList.size() - 1) {
		currentFrame = 0; // 因为没轮播完，所以当前帧序号从0开始
	}

	PngChunkFCTL pngChunk = fctlArrayList.get(currentFrame);

	int delayNum = pngChunk.getDelayNum();
	int delayDen = pngChunk.getDelayDen();
	int delay = Math.round(delayNum * DELAY_FACTOR / delayDen);

	scheduleSelf(this, SystemClock.uptimeMillis() + delay); // 定时器，循环走run
	invalidateSelf(); // 通知draw再一次了
}

public void stop() {
	if (isRunning()) {
		currentLoop = 0;
		unscheduleSelf(this); // 停止定时器
		isRunning = false;
		if (apngListener != null) apngListener.onAnimationEnd(this);
	}
}

public void draw(Canvas canvas) {
	if (currentFrame <= 0) { 
		drawBaseBitmap(canvas);
	} else {
		drawAnimateBitmap(canvas, currentFrame);
	}

	if (!showLastFrameOnStop && numPlays > 0 && currentLoop >= numPlays) {
		stop(); // 不轮播了就停止
	}

	if (numPlays > 0 && currentFrame == numFrames - 1) { // 最后一帧了
		currentLoop++; // 循环次数加一
		if (apngListener != null) apngListener.onAnimationRepeat(this);
	}
	currentFrame++;
}

private void drawAnimateBitmap(Canvas canvas, int frameIndex) {
	Bitmap bitmap = getCacheBitmap(frameIndex); // 这里对帧bitmap做了缓存
		if (bitmap == null) {
			bitmap = createAnimateBitmap(frameIndex); // 没缓存直接通过帧文件创建bitmap
			cacheBitmap(frameIndex, bitmap); // 缓存！
		}
		if (bitmap == null) return;
		RectF dst = new RectF(0, 0,mScaling * bitmap.getWidth(),mScaling * bitmap.getHeight());
		canvas.drawBitmap(bitmap, null, dst, paint); // 绘制
}