java - 通过Application更新Activity外的TextView

Question

我有以下三个类:

---

public class ApplicationView extends Application {  

    private static Context mContext;
    private static final String    TAG   = "ApplicationView ";  

    public static Context getContext() {
        Log.i(TAG, "getContext: " + mContext); 
        return mContext;
    }

    public static void setContext(Context mmContext) {
        Log.i(TAG, "setContext: " + mmContext);         
        mContext = mmContext;

    }
}

---

    public class VideoCapture extends Activity implements SurfaceHolder.Callback {

        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main); 
            ApplicationView.setContext(this);   
        }
    }

--------------------------
public class OverlayView extends SurfaceView  implements SurfaceHolder.Callback {

    public void updateText()
    {       
        Context mcontext = ApplicationView.getContext();
        ((VideoCapture)mcontext).runOnUiThread(new Runnable(){
                    public void run(){                      
                        String NewText = "bla bla bla"                         
                        TextView txtView = (TextView)findViewById(R.id.txt_status);
                        txtView.setText(NewText);
                    }
                });
    }  
}

---

在我的 list 中:

• 在应用程序中:android:name="xxx.yyy.zzz.ApplicationView"

  - 在 Activity 中:android:name="xxx.yyy.zzz.VideoCapture"

---

当我调用 Update Text 时出现以下 NullPointerException 错误:

02-17 11:15:27.850: E/AndroidRuntime(15834): FATAL EXCEPTION: main
02-17 11:15:27.850: E/AndroidRuntime(15834): java.lang.NullPointerException
02-17 11:15:27.850: E/AndroidRuntime(15834):    at xx.yyy.zzz.OverlayView$2.run(OverlayView.java:137)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at android.app.Activity.runOnUiThread(Activity.java:4591)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at xxx.yyy.zzz.OverlayView.updateText(OverlayView.java:133)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at xxx.yyy.zzz.OverlayView$1.onPreviewFrame(OverlayView.java:122)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at android.hardware.Camera$EventHandler.handleMessage(Camera.java:754)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at android.os.Looper.loop(Looper.java:137)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at android.app.ActivityThread.main(ActivityThread.java:4745)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at java.lang.reflect.Method.invokeNative(Native Method)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at java.lang.reflect.Method.invoke(Method.java:511)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
02-17 11:15:27.850: E/AndroidRuntime(15834):    at dalvik.system.NativeStart.main(Native Method)

---

我做错了什么？在 OverlayView 中调用 updateText 有更好的方法吗？谢谢大家!

Answer 1

我认为当除 Activity 类之外的任何类都知道此 Activity 的布局和/或 View 时，这是一种不好的做法。我的建议是创建在 VideoCapture Activity 中查找和更新 TextView 并在 UI 线程上执行此操作的方法:

public void updateText(final String text) {       
        runOnUiThread(new Runnable() {
                    public void run(){                                               
                        TextView txtView = (TextView)findViewById(R.id.txt_status);
                        txtView.setText(text);
                    }
                });
    }

并将其命名为OverlayView:

Context mcontext = ApplicationView.getContext();
((VideoCapture) mcontext).updateText("bla bla bla");