如何从 Android 中的 PostExecute 正确启动活动? [英] How to correctly start activity from PostExecute in Android?

问题描述

我有一个 AsyncTask，它用来自 Internet 的解析数据填充自定义列表.

I have an AsyncTask, that fills a custom List with parsed data from Internet.

在 PostExecute 中，我填写该列表并准备好将其传输到新活动.

In PostExecute I fill that List and get it ready to transfer it to a new Activity.

我是这样做的:

@Override
protected void onPostExecute(List<VideoDataDescription> result) 
{
    super.onPostExecute(result);
    MainActivity.progressDialog.dismiss();

    context.startActivity(new Intent(context, ResultsQueryActivity.class));


}

上下文

    private Context context;

在执行此代码后的 LogCat 中，我得到一个 Java.lang.NullPointerException.像我一样启动 Activity 是否可能且正确?

In LogCat after executing this code I get a Java.lang.NullPointerException. Is this possible and correct to start an Activity as I do it?

UPD我已经添加

    private Context mContext;


public YoutubeAndYahooParser(Context context) 
{
    super();
    this.mContext = context;
}

初始化上下文并调用

YoutubeAndYahooParser youtubeAndYahooParser = new YoutubeAndYahooParser(ResultsQueryActivity.this);
                    youtubeAndYahooParser.execute("my string to pass in asynctak");

在 PostExecute 之后

After this in PostExecute

Intent intent = new Intent(mContext, ResultsQueryActivity.class);
 intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
 mContext.startActivity(intent);    

我添加了新标志，因为我接下来进入了 LogCat:

I added new flag because of I have got in LogCat the next:

*从活动上下文外部调用 startActivity() 需要 FLAG_ACTIVITY_NEW_TASK 标志.这真的是你想要的吗?*

*Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?*

我说得对吗?

推荐答案

您应该传入应用程序上下文而不是来自本地活动的上下文.IE.使用 context.getApplicationContext() 并将其保存在 AsyncTask 子类中的局部变量中.

You should pass in the application context rather than a context from the local activity. I.e. use context.getApplicationContext() and save that in a local variable in your AsyncTask subsclass.

代码可能如下所示:

public class MyAsyncTask extends AsyncTask {

    Context context;
    private MyAsyncTask(Context context) {
        this.context = context.getApplicationContext();
    }

    @Override
    protected Object doInBackground(Object... params) {
        ...
    }

    @Override
    protected void onPostExecute(List<VideoDataDescription> result) {
        super.onPostExecute(result);
        MainActivity.progressDialog.dismiss();

        context.startActivity(new Intent(context, ResultsQueryActivity.class));
    }
}

你会这样称呼它:

   new MyAsyncTask(context).execute();

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