我试图通过演示使用连续的雷达图像阵列的连续GroundOverlay来在Google地图上显示渐进式雷达图像。为了不使用户界面繁忙,我为此使用了另一个线程。不幸的是,似乎正在发生怪异的NullPointerException。我已经调试了代码,但是没有找到任何可能导致此错误的空变量。

我该怎么办?

我将仅显示相关代码:(请注意,radaroverlay,map,images,image_index和MAP_BOUNDS是全局变量,并且不为null-请参见1)。

编辑-简化了下面的代码。仍然给出完全相同的错误。



public void createLooper() {
    final Runnable runnable = new Runnable() {
        public void run() {
            if(run == true) {
                mHandler.postDelayed(this,500);
            } else {
                return;
            }

            if(radaroverlay != null) {
                radaroverlay.remove();
            }
            // Problem happens in the line below.
            try {
                GroundOverlayOptions opts = new GroundOverlayOptions()
                                             .image(images[image_index])
                                             .positionFromBounds(MAP_BOUNDS)
                                             .transparency((float) 0.3);
                radaroverlay = map.addGroundOverlay(opts);

            } catch (Exception e) {
                e.printStackTrace();
                run = false;
            }

            if(image_index == 19) {
                image_index = 0;
            } else {
                image_index++;
            }
        }
    };
    //mHandler.postDelayed(runnable, 500);
    new Thread(runnable).start();


并对应的logcat



02-27 16:58:04.815: E/AndroidRuntime(6791): FATAL EXCEPTION: main
02-27 16:58:04.815: E/AndroidRuntime(6791): java.lang.NullPointerException
02-27 16:58:04.815: E/AndroidRuntime(6791):     at maps.z.aa.<init>(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at maps.z.bi.a(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at maps.z.bi.b(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at maps.z.ag.addGroundOverlay(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.google.android.gms.maps.internal.IGoogleMapDelegate$Stub.onTransact(IGoogleMapDelegate.java:182)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at android.os.Binder.transact(Binder.java:249)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.google.android.gms.maps.internal.IGoogleMapDelegate$a$a.addGroundOverlay(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.google.android.gms.maps.GoogleMap.addGroundOverlay(Unknown Source)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.aquamet.saramap.MapActivity$2$1.run(MapActivity.java:520)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at android.os.Handler.handleCallback(Handler.java:587)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at android.os.Handler.dispatchMessage(Handler.java:92)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at android.os.Looper.loop(Looper.java:123)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at android.app.ActivityThread.main(ActivityThread.java:4627)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at java.lang.reflect.Method.invokeNative(Native Method)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at java.lang.reflect.Method.invoke(Method.java:521)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:876)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:634)
02-27 16:58:04.815: E/AndroidRuntime(6791):     at dalvik.system.NativeStart.main(Native Method)


调试:

最佳答案

好吧,事实证明,问题是当我使用一个线程更新GroundOverlays时,虽然我可以读取变量(如果是在创建新线程之前由主线程编写的,则是这样),但是我无法写入变量,并且期望主线程得到相同的结果。

这解释了为什么我可以生成opts(从imagesimage_indexMAP_BOUND读取),但是不能使地图设置新的GroundOverlay(写入map对象)。

我最终使用了runOnUiThread而不是线程,它可以处理并发变量问题。

结果代码:



public void createLooper() {
    final Runnable runnable = new Runnable() {
        public void run() {
            if(run == true) {
                mHandler.postDelayed(this,500);
            } else {
                return;
            }
            if(image_index == img_size) {
                image_index = 0;
            }
            if(radaroverlay != null) {
                radaroverlay.remove();
            }
            // Problem happens in the line below.
            try {
                GroundOverlayOptions opts = new GroundOverlayOptions()
                                             .image(images[image_index])
                                             .positionFromBounds(MAP_BOUNDS)
                                             .transparency((float) 0.3);
                radaroverlay = map.addGroundOverlay(opts);
                image_index++;

            } catch (Exception e) {
                e.printStackTrace();
                run = false;
            }
        }
    };
    runOnUiThread(runnable);
}

10-07 22:12