我有一个帮助程序(不是 Activity )类，它对 API 进行查询，该 API 具有一个名为 run() 的公共(public)函数。并在新线程上运行(根据 Android 规范)。我的MainActivity创建一个新的 MakeQuery对象并运行其 run()功能:

MakeQuery q = new MakeQuery();
q.run();

但是，我需要从线程中访问一个变量。下面是一个简短的代码示例:

public class MakeQuery implements Runnable {

    private void setNewString(String localThreadString){
       //NewString comes out null...
       NewString  = localThreadString;
    }

    public void run() {
        new Thread(new Runnable() {
            public void run() {
                android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);

                API Api = new API(keys and tokens);

                //queryAPI() returns string
                setNewString(queryAPI(Api, term1, term2));

                //Don't know how to send intent from here (No context), 
                //I would like:
                Intent i = new Intent(MainActivity.class, AnotherActivity.class)
        }
    }).start();
}

异步任务

//This runs in background thread
@Override
protected Void doInBackground(Void... params) {
    API Api = new API(keys and tokens);

    setNewString(queryAPI(Api, string1, string2));

    return null;
}

@Override
protected void onPostExecute(Void aVoid) {
    Intent intent = new Intent(mContext, Activity2.class);
    intent.putExtra("NewString", NewString);
    Log.d(MYTAG, NewString);
}

主要 Activity

public void buttonPressed(View view) {
    Intent intent = new Intent(this, Activity2.class);
    ...
    MakeQuery task = new MakeQuery(this);
    task.execute();

    startActivity(intent);
}

我尝试在线查看了几个小时。我试过做AsyncTask ，但我不确定如何用我所拥有的实现它。此外，使用 localThread<String>没有帮助。

TLDR:我想知道是否可以获取 NewString，以便我可以通过 Intent 将其传递给另一个 Activity。

解决方案 不要使用 Runnable , 创建一个新的 AsyncTask如下所示。另外，确保 StartActivity在辅助类中而不在 MainActivity 中.这是因为在开始新 Activity 之前我没有等待任务完成。

最佳答案

这是一个使用异步任务的实现:

public class MakeQueryTask extends AsyncTask<Void, Void, Void> {

    private Context mContext;

    private String newString;

    public MakeQueryTask(Context context) {
        mContext = context;
    }

    //This runs on a background thread
    @Override
    protected Void doInBackground(Void... params) {


        API Api = new API(keys and tokens);

        //queryAPI() returns string
        setNewString(queryAPI(Api, term1, term2));

        //You should start your activity on main thread. Do it in onPostExecute() which will be invoked after the background thread is done
        //Intent i = new Intent(mContext, AnotherActivity.class);
        //mContext.startActivity(intent);
        return null;
    }

    private void setNewString(String localThreadString){
        newString  = localThreadString;
    }

    //This will run on UI thread
    @Override
    protected void onPostExecute(Void aVoid) {
        Intent intent = new Intent(mContext, AnotherActivity.class);
       mContext.startActivity(intent);
    }
}

你会这样执行:

 MakeQueryTask task = new MakeQueryTask(this); //Here this is an activity (context)
 task.execute();

关于java - 如何从可运行线程中获取局部变量，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30359961/