如何从可运行线程中获取局部变量

Question

我有一个助手（不是 activity）class 查询 API，它有一个名为 run() 的 public 函数，并且在新线程上运行（根据 Android 规范）。我的 MainActivity 创建一个新的 MakeQuery 对象并运行它的 run() 函数：

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

但是，我需要从线程内访问一个变量。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);
}

我已经试着上网看了好几个小时。我尝试过 AsyncTask，但我不确定如何用我现有的实现它。此外，使用 localThread<String> 没有帮助。

TLDR：我想知道是否有可能获得 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，请确保 StartActivity 在助手 class 中而不是 MainActivity 中。这是因为在开始新的 activity.

之前我没有等待任务完成

Answer 1

如果您从 activity 或 service 调用此 runnable，您可以在构造函数中传入 context。只需在 run() 函数中使用 intent 启动 activity。

public class MakeQuery implements Runnable {

    private Context context;

    public MakeQuery(Context context) {
        this.context = context;
    }

    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));

                Intent intent = new Intent(MainActivity.class, AnotherActivity.class)
                context.startActivity(intent);
        }
    }).start();
}

Answer 2

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();

如何从可运行线程中获取局部变量

How to get a local variable from a Runnable Thread

java

android

multithreading

runnable