Question

我用谷歌搜索了几个小时并尝试了Stack Overflow的所有答案，但没有解决我的问题。

我让android程序以字节为单位下载完美的数据。并下载工作在后台线程。我想显示一个进度对话框（jus Spinning one）。但我真的很讨厌问题。我的下载大约需要5秒，但我的进度对话框未显示或仅显示最后1秒。

这是我的AsyncTask代码。

public class ImageJSON extends AsyncTask<String, String, byte[]> {

private JSONObject jsonObject = new JSONObject();
private byte[] response;

 private ProgressDialog pg; 
 private Context context; 

 public ImageJSON(Activity activity) {
     pg = new ProgressDialog(activity);
 }
@Override 
protected void onPreExecute() { 
    super.onPreExecute();
    pg.setMessage("Downloading, please wait.");
    pg.show(); 
} 

@Override 
protected void onProgressUpdate(String... progress) {
    super.onProgressUpdate(progress);
    if (pg != null) { 
        pg.setProgress(Integer.parseInt(progress[0])); 
    } 
}

protected void onPostExecute(byte[] result) { 
    if (pg.isShowing()) { 
        pg.dismiss(); 
    } 
}
@Override
protected byte[] doInBackground(String... params) {
    HttpPost httpPost = new HttpPost("my file url....");
    HttpClient httpClient = new DefaultHttpClient();
    HttpContext httpContext = new BasicHttpContext();
    try {
        jsonObject.put("imageId", params[0]);

        StringEntity stringEntity = new StringEntity(jsonObject.toString());
        httpPost.addHeader("Content_Type", "application/octet_stream");
        httpPost.setEntity(stringEntity);

        HttpResponse httpResponse = httpClient.execute(httpPost, httpContext);
        HttpEntity entity = httpResponse.getEntity();

        if (entity!=null) {
            response = EntityUtils.toByteArray(entity);
            entity.consumeContent();
            httpClient.getConnectionManager().shutdown();
        }
    } catch (JSONException|IOException e) {
        e.printStackTrace();
    }
    return response;
}

我使用此代码从我的活动中调用它。

final ImageJSON imageTask = new ImageJSON(ReaderActivity.this);
byte[] response = imageTask.execute(imageId).get();

如果有人可以帮助我，请提前致谢。

Answer 1

您不希望使用get()，因为它仍会冻结您的UI线程，从而否定使用AsyncTask的意义。您可能希望实施onPostExecute以便正确返回结果。

Answer 2

试试这个 -

public ImageJSON(Activity activity) {

 }
@Override 
protected void onPreExecute() { 
    super.onPreExecute();
pg = new ProgressDialog(ReaderActivity.this);
    pg.setMessage("Downloading, please wait.");
    pg.show(); 
}

Answer 3

您忘记在onPreExecute方法中初始化您的进度对话

@Override 
protected void onPreExecute() { 
    super.onPreExecute();
pg = new ProgressDialog(pass_context_here);
    pg.setMessage("Downloading, please wait.");
    pg.show(); 
}

Answer 4

更改此

public ImageJSON(Context ctx) {
 this.context = ctx;

}

现在在onPreExecute()方法中使用此

@Override 
protected void onPreExecute() { 
 super.onPreExecute();
 pg = new ProgressDialog(context);
 pg.setMessage("Downloading, please wait.");
 pg.show(); 
 }

您在ProgressDialog类中初始化ImageJSON，阻止您的UI线程意味着将其冻结。因此需要参考上下文在onPreExecute()方法中初始化它。

执行AsyncTask期间不显示进度对话框

4 个答案: