Question

我有一个CountDownTimer，它每隔15秒调用一次ChangeWallpaper（）方法。壁纸会改变，但是当我尝试打开应用程序时，它会使应用程序抽屉屏幕无响应几秒钟。当应用程序最终打开时，我选择的所有内容都需要5-10秒才能响应。我在Android Developer中读到了AsyncTask，它应该在UI线程之外加载Bitmaps并阻止App挂起，但它似乎没有用。

以下代码位于我的Activity类中：

/** changeWallpaper() **/ - called by CountDownTimer every 15 seconds
protected void changeWallpaper() throws IOException {
    Integer totalimages = finallist.size();

    if (lastloopcount == totalimages) { // if end of the list of images is reached, it resets and goes back to top.
        loopcount = 0;
        lastloopcount = 0;
    }

    for (String imagepath : finallist) { // "finallist" is global variable with all the image's paths in an array list. The Loop count is to select the next image in the array list every 15 seconds.
        loopcount++;
        if (loopcount > lastloopcount) {
            lastloopcount = loopcount;
            loopcount = 0;

            WallpaperManager wm = WallpaperManager.getInstance(this);
            wm.setBitmap(decodeImageFromPath(imagepath));

            break;
        }
    }
}

/** AsyncTask Wallpaper Load **/
class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {
    public BitmapWorkerTask(ImageView imageView) {
        new WeakReference<ImageView>(imageView);
    }

    @Override
    protected Bitmap doInBackground(Integer... params) {
        return null;
    }
}

/** decodeImageFromPath() **/
public Bitmap decodeImageFromPath(String imagepath) {
    DisplayMetrics displayMetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    int height = displayMetrics.heightPixels;
    int width = displayMetrics.widthPixels << 2;

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(imagepath, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, width, height);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeFile(imagepath, options);
}

/** WallpaperManager (Method) **/
public static int calculateInSampleSize(
    BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // ... Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;

    int stretch_width = Math.round((float)width / (float)reqWidth);
    int stretch_height = Math.round((float)height / (float)reqHeight);

    if (stretch_width <= stretch_height) return stretch_height;
    else return stretch_width;
}

我是否正确使用了AsyncTask功能？
有更简单的方式来写这个吗？

提前致谢。

编辑：

/** Spinner **/
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
    String chosenTime = parent.getItemAtPosition(position).toString();
    int chosenTimeNew = 0;
    if (chosenTime.contains("sec")) {
        chosenTime = chosenTime.replace(" sec","");
        chosenTimeNew = Integer.parseInt(chosenTime) * 500;
    } else if (chosenTime.contains("min") ) {
        chosenTime = chosenTime.replace(" min","");
        chosenTimeNew = Integer.parseInt(chosenTime) * 30000;
    } else if (chosenTime.contains("hour")) {
        chosenTime = chosenTime.replace(" hour","");
        chosenTimeNew = (Integer.parseInt(chosenTime) * 30000) * 60;
    } else if (chosenTime.contains("day")) {
        chosenTime = chosenTime.replace(" day","");
        chosenTimeNew = ((Integer.parseInt(chosenTime) * 30000) * 60) * 24;
    }
    rSpeed = chosenTimeNew;
}

编辑2：

由CountDownTimer（）调用：

new BitmapWorkerTask(null).execute(imagepath);

然后：

    /** AsyncTask Wallpaper Load **/
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {

    public BitmapWorkerTask(ImageView imageView) {
        new WeakReference<ImageView>(imageView);
    }

    @Override
    protected Bitmap doInBackground(String... params) {

        DisplayMetrics displayMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
        int height = displayMetrics.heightPixels;
        int width = displayMetrics.widthPixels << 2;

        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(params[0], options);

        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, width, height);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;

        Bitmap bmp = BitmapFactory.decodeFile(params[0], options);
        return bmp;
    }

    protected void onPostExecute(Bitmap bmp) {

        Context context = getApplicationContext();
        WallpaperManager wm = WallpaperManager.getInstance(context);
        try {
            wm.setBitmap(bmp);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

    /** WallpaperManager (Method) **/
public static int calculateInSampleSize(
    BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // ... Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;

    int stretch_width = Math.round((float)width / (float)reqWidth);
    int stretch_height = Math.round((float)height / (float)reqHeight);

    if (stretch_width <= stretch_height) return stretch_height;
    else return stretch_width;
}

Answer 1

应该在doInBackground方法中调用主代码（处理位图）。否则它与此处的同步调用相同。

    @Override
    protected Bitmap doInBackground(String... params) {
        Bitmap bmp = decodeImageFromPath(params[0]);
        return bmp;
    }

     protected void onPostExecute(Bitmap bmp) {
        wm.setBitmap(bmp)
     }

new BitmapWorkerTask ().execute(imagePath);

http://developer.android.com/reference/android/os/AsyncTask.html

您可以参考此链接上的示例。

Answer 2

您甚至不使用BitmapWorkerTask！当你在代码中写一些AsyncTask时，没有任何魔法能够在后台执行代码的任意部分。你知道，你也必须使用它。

将代码的持久部分移动到AsyncTask的doInBackground()方法中，然后调用它：new BitmapWorkerTask().execute();

修改

要传递图像路径，请将BitmapWorkerTask的定义更改为类似... extends AsyncTask<String, Void, Bitmap> ...的内容（请注意字符串而不是整数），并将图像路径作为execute()方法的参数。

new BitmapWorkerTask().execute(imagePath);

请注意，现在这是异步运行的，所以execute（）调用会立即返回，但是加载图像还需要一些时间。

另请阅读Painless Threading文章。

加载位图时，应用程序UI变得无法响应

2 个答案: