Question

如何在执行任务时使用AsyncTask类来显示对话框???

class TestAsynTask extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        ProgressDialog.show(???, null, null);
        super.onPreExecute();
    }
    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub
        return null;
    }

}

Answer 1

假设TestAsyncTask是Activity的内部类，那么您可以使用活动名称.this来获取上下文。如果TestAsyncTask不是内部类，那么您需要将Activity的实例传递给构造函数，以便可以将Context作为ProgressDialog.show()方法提供。

以下是内部类方法的示例：

class MyActivity extends Activity {
    //Activity Lifecycle methods

    class TestAsynTask extends AsyncTask<Void, Void, Void> {
        ProgressDialog dialog;

        @Override
        protected void onPreExecute() {
            dialog = ProgressDialog.show(MyActivity.this, "title", "message");
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... params) {
            //very long computation...
            return null;
        }

        @Override
        protected void onPostExecute(Void void) {
           dialog.cancel();
        }
    }
}

您会注意到，您应该将ProgressDialog保存到onPreExecute()方法中的实例变量，然后使用cancel()方法调用onPostExecute()。

另一种方法看起来很相似：

class MyActivity extends Activity {
    //Activity Lifecycle methods


}

class TestAsynTask extends AsyncTask<Void, Void, Void> {
    ProgressDialog dialog;
    MyActivity activity;        

    TaskAsynTask(MyActivity activity) {
        this.activity = activity;
    }

    @Override
    protected void onPreExecute() {
        dialog = ProgressDialog.show(activity, "title", "message");
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... params) {
        //very long computation...
        return null;
    }

    @Override
    protected void onPostExecute(Void void) {
        dialog.cancel();
    }
}

用于显示对话框的AsyncTask

1 个答案: