java - 进度对话框未出现

Question

我有在 AsyncTask 中启动 ProgressDialog 的代码，它看起来像这样:

class RetrieveApps extends AsyncTask<String, Void, List<ApplicationInfo>> {
    PackageManager pm;

    @Override
    protected List<ApplicationInfo> doInBackground(String...params) {
        dialog = ProgressDialog.show(Apps.this,
                "Retreiving Application list",
                "Retrieving list of installed applications", true);
        pm = getPackageManager();
        return pm.getInstalledApplications(PackageManager.GET_META_DATA);
    }
    @Override
    protected void onPostExecute(List<ApplicationInfo> result) {
        for(ApplicationInfo nfo : result){
            Drawable icon = nfo.loadIcon(pm);
            String name = nfo.loadLabel(pm).toString();
            if(name != null && icon != null){
                apps.add(new App(name, icon));
            }
        }
        dialog.dismiss();
    }

}

我收到一个RuntimeException说

Can't create handler inside thread that has not called Looper.prepare()

它指向调用 ProgressDialog.show() 的行。

Answer 1

public class RetrieveApps extends AsyncTask<String, Void, List<ApplicationInfo>> {
    PackageManager pm;

    @Override
    protected List<ApplicationInfo> doInBackground(String...params) {

        pm = getPackageManager();
        return pm.getInstalledApplications(PackageManager.GET_META_DATA);
    }
    @Override
    protected void onPostExecute(List<ApplicationInfo> result) {
        for(ApplicationInfo nfo : result){
            Drawable icon = nfo.loadIcon(pm);
            String name = nfo.loadLabel(pm).toString();
            if(name != null && icon != null){
                apps.add(new App(name, icon));
            }
        }
        dialog.dismiss();
    }

    @Override
    protected void onPreExecute(){
      dialog = ProgressDialog.show(Apps.this,
                "Retreiving Application list",
                "Retrieving list of installed applications", true);

    }

}

尝试上面的类，我将对话框创建移到了在 UI 线程上运行的 onPreExecute 方法中

记住 onPreExecute 、 onPostExecute 和 onProgressUpdate 方法在 UI 线程上运行doInBackground方法在非UI线程上运行