我正在为学校创建一个项目,其中包含 map fragment 和按钮,但是当我尝试访问我的 map 时,它完全崩溃了 这是我的代码:
package com.helloandroid.mapview;
import android.app.FragmentManager;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import com.google.android.gms.maps.*;
import com.google.android.gms.maps.model.*;
public class MainActivity extends ActionBarActivity {
GoogleMap myMap;
Button btnShow;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
btnShow = (Button) findViewById(R.id.btnShow);
这是崩溃的地方:
SupportMapFragment mapFrag = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
myMap = mapFrag.getMap();
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
这是我的 logcat 结果:
01-09 20:19:57.475 28744-28744/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.helloandroid.mapview/com.helloandroid.mapview.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2306)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
at android.app.ActivityThread.access$600(ActivityThread.java:156)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1340)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:153)
at android.app.ActivityThread.main(ActivityThread.java:5297)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.helloandroid.mapview.MainActivity.onCreate(MainActivity.java:34)
at android.app.Activity.performCreate(Activity.java:5122)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
at android.app.ActivityThread.access$600(ActivityThread.java:156)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1340)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:153)
at android.app.ActivityThread.main(ActivityThread.java:5297)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
这是 map fragment
<fragment
android:id="@+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.google.android.gms.maps.MapFragment"
android:layout_below="@+id/btnShow" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Show"
android:id="@+id/btnShow"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
有人知道我该如何解决这个问题吗?
提前致谢
最佳答案
正确设置
首先您需要检查设备是否有正确的 Google Play 服务,如果没有正确设置,您将根本无法使用 map 。
if (GooglePlayServicesUtil.isGooglePlayServicesAvailable(this) != ConnectionResult.SUCCESS) {
// Handle the case here
}
其次,您无法保证 map 已准备好,因此您需要多次尝试设置 map ,例如从 OnCreate(..)
和 onResume(..)
调用此方法。
private void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the map.
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
// Check if we were successful in obtaining the map.
if (mMap != null) {
// here you can setup the map the way you want
}
}
}
你的错误
当您访问 SupportMapFragment 时,您收到 NullPointerException
吗?检查以下内容:
- 您确定已包含 android-support-v4.jar 支持库吗?
- 您确定 R.id.map 存在吗?
- 您的项目中是否正确包含了 Google Play 服务库?
如果您仍然遇到问题,您应该包含 map fragment 的 xml。
编辑
你的 XML 设置应该有这个
class="com.google.android.gms.maps.SupportMapFragment"
,即从 fragment 中删除 android:name
属性并添加类。
关于java - 尝试访问 map fragment 时应用程序崩溃,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21029015/