在Android线程上更改图像 [英] Changing image on Android thread

问题描述

我经历了stackoverflow和所有类似的答案-但发现它们没有用.

I've gone through stackoverflow and all the similar answers - but have found them not of use.

任何人都可以指出为什么这行不通吗?它应该很简单:每6秒钟更新一次图片(每3分钟更新一次，但为了进行测试，我将其设为6秒钟).

Can anyone please point out why this is not working? It should be simple: update the image every 6 seconds (will be every 3 mins but for testing I've put it as 6 seconds).

代码的作用是-逐步浏览4个图像中的每个图像，但不更改图像.但是，当它到达最后一张图像时，它确实会更改它(??).

What the code does is - goes through each of the 4 images step by step but does not change the image. HOWEVER when it gets to the last image - it does change it(??).

问题:

1. 这是怎么了?
2. 为什么只更新最后一张图片?
3. 如果我仅向处理程序添加"post"而不是"postDelayed"来启动代码-平板电脑只会停留在黑屏上.为什么我必须延迟启动代码才能使其正常工作?

int currentIndex = 0;
boolean start = false;
ImageView descriptionImage;
private Runnable timerRunnable;
long startTime = 0;
private Handler handler;

int[] pictureIds = new int[]{R.drawable.hang, R.drawable.dog, R.drawable.coffee, R.drawable.about};

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    pictureDescription = new ArrayList<String>();
    handler = new Handler(Looper.getMainLooper());
}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_picture_test, container, false);
    descriptionImage = (ImageView) v.findViewById(R.id.iv_picture);

    return v;
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    start();
}

private void start() {

    start = true;
    startTime = System.currentTimeMillis();
    loadImage();
    timerRunnable = new Runnable() {

        @Override
        public void run() {
            while (start) {
                long time = System.currentTimeMillis() - startTime;
                float mins = (float) time / (60 * 1000);
                if (mins >= 0.1f) {
                    startTime = System.currentTimeMillis();
                    if (currentIndex < pictureIds.length) {
                        currentIndex++;
                        loadImage();
                    }
                }
            }
        }
    };
    handler.postDelayed(timerRunnable, 1000);
}

private void loadImage() {
    getActivity().runOnUiThread(new Runnable() {
        @Override
        public void run() {
            if (currentIndex < pictureIds.length) {
                descriptionImage.setImageResource(pictureIds[currentIndex]);
            } else {
                start = false; // finish
            }

        }
    });
}

谢谢！

如果我也将它发布到imageview线程而不是处理程序，则不起作用.

Doesn't work if I post it to the imageview thread either, instead of the handler.

descriptionImage.postDelayed(timerRunnable，1000);

descriptionImage.postDelayed(timerRunnable, 1000);

推荐答案

这是怎么了?

当UI线程繁忙时( while(start))，等待条件变为真( if(mins> = 0.1f){)，它无法照顾其余的工作(例如绘图).

while the UI Thread is busy ( while (start) ) , waiting to your condition to became true ( if (mins >= 0.1f) { ), it can't take care of the rest (like drawing).

Why would it only update the last image?

因为它只能在 if(currentIndex< pictureIds.length){不为真， start 为假，并且UI线程最终可以绘制时才绘制

because it can draw only when if (currentIndex < pictureIds.length) { is not true, start becomes false, and the UI thread can finally draw

如果我仅通过处理程序的"post"(而不是一个"post")来启动代码"postDelayed"-平板电脑仅停留在黑屏上.我为什么会必须延迟启动代码才能使其正常工作?

If I start the code with just a "post" to the handler instead of a "postDelayed" - the tablet just stays with a black screen. Why do I have to start the code with a delay to make it work?

请参阅第1点.

如果您想每3秒更改一次图像，则可以继续使用Handler#postDelayed.例如

if you want to change your image every 3 seconds, you could keep using Handler#postDelayed. E.g.

start = true;
startTime = System.currentTimeMillis();
loadImage();
timerRunnable = new Runnable() {

    @Override
    public void run() {
        currentIndex = currentIndex++ % pictureIds.length;
        loadImage();
        handler.postDelayed(this, 3000);
    }
};
handler.postDelayed(timerRunnable, 3000);

这篇关于在Android线程上更改图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！