下载图像时显示 ProgressDialog

Question

我的应用程序具有下载功能需要一些时间来下载图像，因为我在下载图像时尝试添加ProgressDialog。 ProgressDialog它永远不会出现请帮助我

这是我保存图像的代码：

private String saveImage(Bitmap image) {
    ProgressDialog pd = new ProgressDialog(Pop.this);
    pd.setMessage("Downloading ...");
    pd.show();
    String savedImagePath = null;
    String imageFileName = "vapor"+System.currentTimeMillis()+ ".png";
    File storageDir = new File(
            Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)
                    + "/vaporwave");
    boolean success = true;
    if (!storageDir.exists()) {
        success = storageDir.mkdirs();
    }
    if (success) {
        File imageFile = new File(storageDir, imageFileName);
        savedImagePath = imageFile.getAbsolutePath();
        try {
            OutputStream fOut = new FileOutputStream(imageFile);
            image.compress(Bitmap.CompressFormat.PNG, 100, fOut);
            fOut.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        // Add the image to the system gallery
        galleryAddPic(savedImagePath);
        Toast.makeText(Pop.this, "IMAGE SAVED", Toast.LENGTH_LONG).show();
        pd.dismiss();
    }
    return savedImagePath;
}

Answer 1

你应该使用像AsyncTask这样的后台任务，你不应该在你的UI线程上做复杂的任务。（否则你的UI会很幸运直到任务完成，所以你的progressDialog永远不会显示）

您可以阅读 AsyncTask Here

例如在异步中：

1) 在onPreExecute 上显示你的progressDialog

2) 并在onPostExecute 中将其关闭

3) 并在doInBackground 中完成您的工作（保存图像）（此方法中的返回类型将传递给onPostExecute）

public class saveImage extends AsyncTask<Bitmap,Void,String>{
    ProgressDialog pd;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = new ProgressDialog(Pop.this);
        pd.setMessage("Downloading ...");
        pd.show();
    }

    @Override
    protected String doInBackground(Bitmap... params) {
        Bitmap image = params[0];
        String savedImagePath = null;
        String imageFileName = "vapor"+System.currentTimeMillis()+ ".png";
        File storageDir = new File(
                Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)
                        + "/vaporwave");
        boolean success = true;
        if (!storageDir.exists()) {
            success = storageDir.mkdirs();
        }
        if (success) {
            File imageFile = new File(storageDir, imageFileName);
            savedImagePath = imageFile.getAbsolutePath();
            try {
                OutputStream fOut = new FileOutputStream(imageFile);
                image.compress(Bitmap.CompressFormat.PNG, 100, fOut);
                fOut.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            // Add the image to the system gallery
            galleryAddPic(savedImagePath);
            Toast.makeText(Pop.this, "IMAGE SAVED", Toast.LENGTH_LONG).show();
            pd.dismiss();
        }
        return savedImagePath;
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);
        //s is your savedImagePath
        pd.dismiss();
    }
}

你可以这样调用这个任务：

    new saveImage().execute(yourBitmap);