从 activity 调用 mapfragment

Question

我将 GoogleMap 定义为：

fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.gms.maps.MapView
        android:id="@+id/mapView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    </RelativeLayout>

和

fragment.java

public class SecondFragment extends Fragment implements onMapReadyCallback {

    private GoogleMap mMap;

    public static SecondFragment newInstance() {
        SecondFragment fragment = new SecondFragment();
        return fragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.activity_maps, null, false);

        SupportMapFragment mapFragment = (SupportMapFragment) this.getChildFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

        return view;
    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}

我的主要 activity 是：

import android.content.pm.PackageManager;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.DialogFragment;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import android.widget.TextView;

import com.google.android.gms.maps.GoogleMap;


public class MainActivity extends AppCompatActivity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
        pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        //mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        //mViewPager = (ViewPager) findViewById(R.id.container);
        //mViewPager.setAdapter(mSectionsPagerAdapter);

        //Get Location Permission
        if (ContextCompat.checkSelfPermission(getApplicationContext(),
                android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(getApplicationContext(),
                        android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {

            ActivityCompat.requestPermissions(this, new String[]
                    {android.Manifest.permission.ACCESS_FINE_LOCATION,
                            android.Manifest.permission.ACCESS_COARSE_LOCATION}, 101);

        }

        // Tab to get Date TODO: Expand fo both Location and Date
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showDateDialog();
            }
        });

    }

    public void showDateDialog() {
        DialogFragment CalFragment = new CalFragment();
        CalFragment.show(getSupportFragmentManager(), "timePicker");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    private class MyPagerAdapter extends FragmentPagerAdapter {

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
        }


        @Override
        public Fragment getItem(int pos) {
            switch (pos) {

                case 0:
                    return FirstFragment.newInstance("FirstFragment, Instance 1");
                case 1:
                    return SecondFragment.newInstance();
                case 2:
                    return ThirdFragment.newInstance("ThirdFragment, Instance 1");
                case 3:
                    return ThirdFragment.newInstance("ThirdFragment, Instance 2");
                case 4:
                    return ThirdFragment.newInstance("ThirdFragment, Instance 3");
                default:
                    return ThirdFragment.newInstance("ThirdFragment, Default");
            }
        }

        @Override
        public int getCount() {
            return 5;
        }
    }
}

表示无法解析 mMap 符号。我应该如何从 activity 调用地图？我这里哪里出错了？

我正在使用 android-support-v4。

Answer 1

首先，您不能创建片段：

return SecondFragment(GoogleMap mMap);

因为您的 SecondFragment 上只有一个默认构造函数，即：

public SecondFragment();

或静态方法：

public static SecondFragment newInstance();

创建片段。

而且您也没有使用 new 关键字创建片段。 Java 中的每个对象都需要使用 new 创建。除非你的 SecondFragment(GoogleMap mMap); 是一个方法。

因此，您需要使用以下内容创建片段：

private class MyPagerAdapter extends FragmentPagerAdapter {
    case 1:
       return new SecondFragment.newInstance();
       // or 
       // return new SecondFragment();

要访问 private GoogleMap mMap; 变量，您可以在片段中使用 getter，如下所示：

public class SecondFragment extends Fragment implements onMapReadyCallback {
  private GoogleMap mMap;

  public GoogleMap getMap() {
    return mMap;
  }
  ...
}

Answer 2

我们无法像您需要的那样实例化任何片段。 bcoz参数化构造函数不能用Fragment创建。

使用以下代码更正您的代码：

private class MyPagerAdapter extends FragmentPagerAdapter {
    case 1:
      return new SecondFragment.newInstance(); // replace with this line
    break;
}

从 activity 调用 mapfragment

call mapfragment from activity

android

google-maps-android-api-2