问题描述

大家好，我被困在了一个点上，问题是我有下面显示的三个类，我想在 AsyncTask 类中实例化我的 DatabaseHelper 类.能否请您帮忙，我如何在 AsyncTask 类中获取上下文?

Hi everybody I was stuck at a point, the problem is that I have three classes shown below and I want to instantiate my DatabaseHelper class in AsyncTask class. Could you please help, how can I get context in AsyncTask class?

问题已解决

1. MainActivity 类

1. MainActivity class

public class MainActivity extends Activity {
...
FetchData fetchData = new FetchData();
fetchData.execute();
...
}

public class DatabaseHelper extends SQLiteOpenHelper {
....
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
....
}

public class FetchData extends AsyncTask<String, String, String> {
....
DatabaseHelper db = new DatabaseHelper(); //need context here!!!
....
}

#

感谢 Kasra，我创建了一个 Fourh 类并在调用 AsyncTask 之前在 MainActivity 中使用它

#

Thanks to Kasra, I create a fourh class and use it in MainActivity before calling AsyncTask

1. ContextStatic 类

1. ContextStatic class

public class ContextStatic {
private static Context mContext;

public static Context getmContext() {
    return mContext;
}
public static void setmContext(Context mContext) {
    ContextStatic.mContext = mContext;
}
}

更新了 MainActivity 类

    public class MainActivity extends Activity {
    ...
    ContextStatic.setmContext(this);
    FetchData fetchData = new FetchData();
    fetchData.execute();
    ...
    }

推荐答案

试试这个:

 private class FetchData extends AsyncTask<Context, Void, Void> {
     protected Long doInBackground(Context... c) {
         Context myContext = c[0];
// Do your things here....
     }


     protected void onPostExecute() {
// Insert your post execute code here
     }
 }

您可以通过以下行调用此 AsyncTask - 假设您在活动中:

You can call this AsyncTask by the following line - assuming you are in an activity:

 new FetchData().execute(this);

<小时>

如果你不能改变你的 AsyncTask 减速，那么你可以尝试使用一个静态变量——尽管它不如 AsyncTask 减速那么有效和漂亮.试试这个:

if You cannot change your AsyncTask deceleration, then you can try using a static variable - although it is not as efficient and pretty as AsyncTask deceleration. Try this:

Class myStatic{
private  static Context mContext;


static public void setContext(Context c);
mContext = c;
}

static public Context getContext(){
return mContext;
}

}

在你的主代码中，在你调用 AsyncTask 之前，调用这个:

and in your main code, before you call AsyncTask, call this:

myStatic.setContext(this);

在 AsyncTask 的 doInBackground 方法中，添加:

in your doInBackground method of your AsyncTask, add this:

Context myContext = myStatic.getContext();

这篇关于如何在处理不同类的异步任务类中使用 databasehelper 类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！