Question

首先感谢你的出色工作。论坛对我来说总是很好的帮助，但这次我需要问一个具体的问题。

我创建了一个类Tasks，它将在TextView活动中每秒更新BatteryStatus。我发现有两种方法可以更新文本：

传递对Context接口的引用
在活动类

对于解决方案1，我收到此错误：

09-30 20:08:29.635: W/System.err(14515): android.view.ViewRoot$CalledFromWrongThreadException:      Only the original thread that created a view hierarchy can touch its views.

对于解决方案2，出现此错误：

09-30 21:23:07.110: W/System.err(16344): java.lang.NullPointerException
09-30 21:23:07.110: W/System.err(16344): at android.app.Activity.findViewById(Activity.java:1653)

好的，程序不知道TextView的位置和内容。我需要更改什么才能使其正常工作？我真的想要了解在另一个类中更新TextViews，Buttons ......的两种方法。

传递对Context接口的引用：

public class BatteryStatus extends Activity{

    private static Timer myclock;
    private static TimerTask mytask;
    TextView tvBatteryStatus;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_battery_status);   // XML-Datei im Layout - Ordner

        // Text View
        tvBatteryStatus = (TextView) findViewById(R.id.tvBatteryStatus);

        // Timer Task
        myclock = new Timer();
        mytask = new Tasks(BatteryStatus.this);
        // schedule the task to run every 1000ms and delay execution for another 1000ms
        myclock.scheduleAtFixedRate(mytask, 1000, 1000);

    }
}

任务

public class Tasks extends TimerTask  {

    Context context;

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

    public void run(){      
        try{Update();}
        catch(Exception e){e.printStackTrace();}
    }

    public void Update(){
        TextView txtView = (TextView) ((BatteryStatus)context).findViewById(R.id.tvBatteryStatus);
        txtView.setText("Hello");
    }

}

在活动类

带吸气剂的BatteryStatus

    public class BatteryStatus extends Activity{

        private static Timer myclock;
        private static TimerTask mytask;
        TextView tvBatteryStatus;

        @Override
        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_battery_status);   // XML-Datei im Layout - Ordner

            // Text View
            tvBatteryStatus = (TextView) findViewById(R.id.tvBatteryStatus);

            // Timer Task
            myclock = new Timer();
            mytask = new Tasks();
            // schedule the task to run every 1000ms and delay execution for another 1000ms
            myclock.scheduleAtFixedRate(mytask, 1000, 1000);

        }

        public TextView getTextView(){
            TextView tV = (TextView)findViewById(R.id.tvBatteryStatus);
            return tV;
        }

    }

任务

    public class Tasks extends TimerTask  {

        TextView t;
        BatteryStatus b = new BatteryStatus();

        public void run(){      
            try{Update();}
            catch(Exception e){e.printStackTrace();}
        }

        public void Update(){
            t = b.getTextView();
            t.setText("hellooo");
        }

    }

Answer 1

快速而肮脏的解决方案：

编辑Tasks类：

    public class Tasks extends TimerTask  {

        TextView t;
        Activity activity;
        BatteryStatus b = new BatteryStatus();

        public void run(){      
            try{Update();}
            catch(Exception e){e.printStackTrace();}
        }

        public void Update(){
            if(activity != null){
                activity.runOnUIThread(new Runnable(){
                    t = b.getTextView();
                    t.setText("hellooo");
                });
            }            
        }
        public void setActivity(Activity a){ // this must be called from the rest of your application
            activity = a;
        }

    }

Answer 2

使用第二种方法，您将实例化一个新的Activity，而不是使用已初始化TextView的Activity。您必须在构造函数中提供活动的引用。

    public Tasks(BatteryStatus b){this.b = b;}

你可以使用textView。

Answer 3

android中的基本拇指规则是你只能在主线程上更新视图，因此你得到了异常

 09-30 20:08:29.635: W/System.err(14515): android.view.ViewRoot$CalledFromWrongThreadException:      Only the original thread that created a view hierarchy can touch its views.

它告诉您正在从非UI线程访问视图元素。因此，为了从非UI线程进行视图更改，请参阅此网站并阅读主题部分。它所需要的一切...... http://developer.android.com/guide/components/processes-and-threads.html

Answer 4

针对您在第二个解决方案中遇到的问题在活动类中创建一个getter函数

您必须通过构造函数传递Context引用。

 public class Tasks extends TimerTask  {

        TextView t;
        BatteryStatus b = new BatteryStatus();

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

        public void run(){      
            try{Update();}
            catch(Exception e){e.printStackTrace();}
        }

        public void Update(){
             TextView txtView = (TextView) ((Activity)context).findViewById(R.id.tvBatteryStatus);
              txtView.setText("Hello");
        }

    }

并在此类中创建Tasks对象，并将此BatteryStatus活动的上下文传递给Tasks.class

 public class BatteryStatus extends Activity{

        private static Timer myclock;
        private static TimerTask mytask;
        TextView tvBatteryStatus;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_battery_status);   // XML-Datei im Layout - Ordner

        // Text View
        tvBatteryStatus = (TextView) findViewById(R.id.tvBatteryStatus);

        // Timer Task
        myclock = new Timer();
        mytask = new Tasks();
        // schedule the task to run every 1000ms and delay execution for another 1000ms
        myclock.scheduleAtFixedRate(mytask, 1000, 1000);
        // make an object and pass the reference of this activity
        Tasks abc = new Tasks(BatteryStatus .this);
    }



}

通过TimerTask从另一个类更新Activity的TextView的两个选项

4 个答案: