从布局创建的 onCreate() 中的 getMap() 给出 nullpointerexception [英] getMap() in onCreate(), created from layout gives nullpointerexception

问题描述

这是我的代码:

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;

在 onCreate() 方法中:(我在 onCreate() 中只有这个，除了包创建和变量分配，使用那个包.)

Inside onCreate() method:(I have only this at onCreate(), aside a bundle creation and variables asignation, using that bundle.)

FragmentManager myFM = getSupportFragmentManager();
SupportMapFragment myMAPF =(SupportMapFragment)myFM.
      findFragmentById(R.id.mapfragment);
map=myMAPF.getMap();//Exception at this line

布局:

<fragment
    android:id="@+id/mapfragment"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/button"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true" />

清单:

<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="myapikey" />

不得不提的是，当我生成api密钥时，我复制了debug.keystore文件并存储在一个更方便的位置，然后生成了它.我用原始位置的原始文件再次执行了此操作，并返回了相同的 SH1，但是，我没有生成另一个 API 密钥.已在 API 访问页面中激活中断器.

I have to mention that when i generated the api key I copied the debug.keystore file and stored in a more convenient location, and then generated it. I did it again with the original file in the original location, and returned the same SH1, however, so I didnt generated another API key. Have activated the interruptor in the API Access page.

我之前看过一些回答同样的问题，我尝试了很多他们的解决方案......但没有运气.

I have seen some answer asking the same thing before, and I have tried a lot of their solutions... without luck.

我正在 Eclipse 的 Android 4.0 版设备上通过 USB 运行该应用程序.

I am running the app on a device with Android version 4.0, via USB, from Eclipse.

谁能帮我找出错误在哪里?谢谢.

Anyone can help me to find where is the error? Thank you.

编辑

抱歉，忘记了 StackTrace

Sorry, forgot the StackTrace

10-23 13:54:53.230: E/AndroidRuntime(6786): java.lang.RuntimeException: Unable to start activity ComponentInfo{mypackage/mypackage.MapActivity}: java.lang.NullPointerException
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.os.Looper.loop(Looper.java:137)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread.main(ActivityThread.java:4424)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at java.lang.reflect.Method.invokeNative(Native Method)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at java.lang.reflect.Method.invoke(Method.java:511)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:817)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at dalvik.system.NativeStart.main(Native Method)
10-23 13:54:53.230: E/AndroidRuntime(6786): Caused by: java.lang.NullPointerException
10-23 13:54:53.230: E/AndroidRuntime(6786):     at mypackage.MapActivity.onCreate(MapActivity.java:73)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.Activity.performCreate(Activity.java:4470)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
10-23 13:54:53.230: E/AndroidRuntime(6786):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)

我刚刚注意到一个奇怪的事情，在堆栈跟踪的第一行中放了两倍于我的应用程序的完整包......为什么会发生这种情况?

I just noticed a strange thing, in the first line of the stacktrace puts twice the full package of my app...why is this happening?

推荐答案

您的地图尚不可用...在使用 Play 服务之前，您可以使用类似以下方法来确定它们是否可用(我会调用它在 onActivityCreated，而不是 onCreate) :

Your Map is not yet available... You can use something like the following method to determine if Play Services are available before making use of them (I would call it in onActivityCreated, rather than onCreate) :

protected boolean isPlayServicesAvailable() {
    int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);

    if (status == ConnectionResult.SUCCESS) {
        return (true);
    } else if (GooglePlayServicesUtil.isUserRecoverableError(status)) {
        // deal with error
    } else {
            // maps is not available
    }

    return (false);
}

此外，您的 Fragment 需要实现 Play 服务所需的回调(接口 GooglePlayServicesClient.ConnectionCallbacks 和 GooglePlayServicesClient.OnConnectionFailedListener :

Also, your Fragment needs to implement the Callbacks required by the Play Services (interfaces GooglePlayServicesClient.ConnectionCallbacks and GooglePlayServicesClient.OnConnectionFailedListener :

    /*
     * Called by Location Services when the request to connect the
     * client finishes successfully. At this point, you can
     * request the current location or start periodic updates
     */
    @Override
    public void onConnected(Bundle dataBundle) {
        // Display the connection status
        Toast.makeText(context, "Connected to location services", Toast.LENGTH_SHORT).show();

    }

    /*
     * Called by Location Services if the connection to the
     * location client drops because of an error.
     */
    @Override
    public void onDisconnected() {
        // Display the connection status
        Toast.makeText(context, "Disconnected from location services. Please re-connect.",
                Toast.LENGTH_SHORT).show();
    }

    /*
     * Called by Location Services if the attempt to
     * Location Services fails.
     */
    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        /*
         * Google Play services can resolve some errors it detects.
         * If the error has a resolution, try sending an Intent to
         * start a Google Play services activity that can resolve
         * error.
         */
        if (connectionResult.hasResolution()) {
            try {
                // Start an Activity that tries to resolve the error
                connectionResult.startResolutionForResult(
                        SomeActivity,
                        CONNECTION_FAILURE_RESOLUTION_REQUEST);
                /*
                 * Thrown if Google Play services canceled the original
                 * PendingIntent
                 */
            } catch (IntentSender.SendIntentException e) {
                // Log the error
                e.printStackTrace();
            }
        } else {
            /*
             * If no resolution is available, display a dialog to the
             * user with the error.
             */
            Toast.makeText(context, "Connection error", Toast.LENGTH_SHORT).show();
        }
    }
}

这就是我在包含地图片段的活动中使用它的方式:

EDIT : This is how I use it in my activity containing the map fragment :

if (isPlayServicesAvailable()) {
    setContentView(R.layout.activity_with_map_fragment);
}

在片段中:

if (getMap() != null) {
    GoogleMap map = getMap();
    // do things with the map
}

这应该能让你继续前进;-)

This should get you going ;-)

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