java - Android 应用程序 - 恢复线程

Question

我有一个 Android 应用程序，它有一个运行线程的类。与 here 基本相同.

当前线程每 500 毫秒更新一个带有计算值的 TextView ，并另外记录该值，以便我可以在 adb-logcat 中看到它。

当我使用设备的后退按钮退出应用程序时，线程仍然在后台运行。 (这就是我想要的)。 adb-logcat 仍然给我线程正在计算的值。

但是当我重新打开应用程序时， TextView 不再更新!

当我再次打开应用程序时，我必须做什么才能恢复更新 TextView ？

这是我的简化代码:

SensorProcessor.java

public class SensorProcessor implements Runnable {

    protected Context mContext;
    protected Activity mActivity;

    private volatile boolean running = true;
    //Tag for Logging
    private final String LOG_TAG = SensorProcessor.class.getSimpleName();

    public SensorProcessor(Context mContext, Activity mActivity){
        this.mContext = mContext;
        this.mActivity = mActivity;
    }


    public void run() {

            while (running){

                try {                    
                    final String raw = getSensorValue();
                    mActivity.runOnUiThread(new Runnable() {
                        public void run() {
                            final TextView textfield_sensor_value;
                            textfield_sensor_value = (TextView) mActivity.findViewById(R.id.text_sensor);
                            textfield_sensor_value.setText("Sensor Value: " + raw); // <-------- Does not update the field, when app resumes
                            Log.v(LOG_TAG, raw); // <-------- Still working after the app resumes
                        }
                    });


                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    //When an interrupt is called, we set running to false, so the thread can exit nicely
                    running = false;
                }
            }

            Log.v(LOG_TAG, "Sensor Thread finished");

    }
}

MainActivity.java

public class MainActivity extends Activity implements OnClickListener, OnInitListener {
    //Start the Thread, when the button is clicked
    public void onClick(View v) {
        if (v.getId() == R.id.button_start) {
            runnable = new SensorProcessor(this.getApplicationContext(),this);
            thread = new Thread(runnable);
            thread.start();
        }
}

Answer 1

您可以扩展 Application 类并将 getter 和 setter 方法插入到您的 Runnable 中。下面是 MyApplication 的示例(不要忘记添加 list 连接!)，在 manifest.xml 中:

<application
    android:name=".MyApplication"
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppBaseTheme" >

然后是我的应用程序:

public class MyApplication extends Application {

    private SensorProcessor mSensorProcessor = null;

     public SensorProcessor getCurrentSensorProcessor(){
        return mSensorProcessor;
     }

      public void setSensorProcessor(SensorProcessor mSensorProcessor){
          this.mSensorProcessor = mSensorProcessor;
     }

}

在您的 Activity 的 onCreate() 内调用:

 ((MyApplication)getApplication()).getCurrentSensorProcessor().mActivity = this;

您还需要修改 Runnable 构造函数:

public SensorProcessor(Context mContext, Activity mActivity){
    this.mContext = mContext;
    this.mActivity = mActivity;
    ((MyApplication)mActivity.getApplication()).setSensorProcessor(this);
}

并且不要忘记在完成时通过在 Runnable 中调用它来清空 mSensorProcessor 的实例:

((MyApplication)mActivity.getApplication()).setSensorProcessor(null);

最后您需要修改 Activity 中的 onClick:

 if (v.getId() == R.id.button_start) {
        SensorProcessor mSensorProcessor = ((MyApplication)getApplication()).getCurrentSensorProcessor();
        if (mSensorProcessor != null)
            mSensorProcessor.mActivity = this;
        else {
            runnable = new SensorProcessor(this.getApplicationContext(), this);
            thread = new Thread(runnable);
            thread.start();
        }
    }

它应该可以工作，也许需要一些小的改变。