如何从衍生的后台服务访问原始活动的视图

Question

我有一个名为A的活动,在选择菜单项0时,它产生服务B,它在新线程中启动一个可运行的C. 我在活动A中有一个TextView,我想在线程C中访问它.

我已经尝试将TextView作为公共静态字段,但这会产生以下错误:

07-21 07:26:25.723: ERROR/AndroidRuntime(1975): android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.checkThread(ViewRoot.java:2440)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.invalidateChild(ViewRoot.java:522)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewRoot.invalidateChildInParent(ViewRoot.java:540)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.ViewGroup.invalidateChild(ViewGroup.java:2332)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.view.View.invalidate(View.java:4437)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.updateAfterEdit(TextView.java:4593)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.handleTextChanged(TextView.java:5932)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:6081)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.sendTextChange(SpannableStringBuilder.java:889)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:352)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:269)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:432)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:259)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.text.SpannableStringBuilder.append(SpannableStringBuilder.java:28)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.append(TextView.java:2191)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at android.widget.TextView.append(TextView.java:2178)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at com.android.peekaboo.DoScan$scanBody.run(DoScan.java:36)
07-21 07:26:25.723: ERROR/AndroidRuntime(1975):     at java.lang.Thread.run(Thread.java:1058)

我也考虑过尝试通过意图传递View,但不知道它是如何工作的.我需要做什么才能做到这一点？

Answer 1

我遇到了类似的问题,需要在单独的线程的Web服务响应上更新ListView.

在分析了类似的问题和示例之后,这里有一个适合您的解决方案:

public class A extends Activity implements Callback {

     callserviceB () { } // where your service B being called;

     @Override
     public void returnServiceResponse() {
          workOnResponse();
          handler.sendEmptyMessage(0);
     }

     private Handler handler = new Handler() {
          public void  handleMessage(Message msg) {
               //update your view from here only.
          }
     }
}

public class B implements Runnable {
     Callback callback;

     public void run() {
         //your business logic.
         callback.returnServiceResponse();
     }
}

public interface Callback {
     public void returnServiceResponse();
}

Answer 2

您必须从GUI线程更新小部件,即"创建视图层次结构的线程".执行此操作的标准方法是通过Handlers,可以在ProgressDialog示例中找到如何使用处理程序的示例(展开'带有第二个线程的示例ProgressDialog').