java - 启动新 Activity ，获取不是封闭类错误

Question

首先，我是 android 和 java 新手。

我有一个使用 facebook 登录的 MainActivity，然后我希望 OnSuccess 启动一个 Map.Activity 类，但它不会，它说该类未包含在内。我无法弄清楚这意味着什么，而且我没有足够的知识将其与其他已回答的主题联系起来。

我的两个类看起来像这样；

MainActivity.java

package com.example.nan.spymap;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;

public class MainActivity extends Activity {

    private CallbackManager callbackManager;

    private TextView info;
    private LoginButton loginButton;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FacebookSdk.sdkInitialize(getApplicationContext());
        callbackManager = CallbackManager.Factory.create();

        setContentView(R.layout.activity_main);



        setContentView(R.layout.activity_main);
        info = (TextView)findViewById(R.id.info);
        loginButton = (LoginButton)findViewById(R.id.login_button);

        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                startActivity(new Intent(MapActivity.this, MapActivity.class));

            }

            @Override
            public void onCancel() {
                info.setText("Login attempt cancelled.");
            }

            @Override
            public void onError(FacebookException e) {
                info.setText("Login attempt failed.");
            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        callbackManager.onActivityResult(requestCode, resultCode, data);
    }
}

和MapActivity.java

package com.example.nan.spymap;

import android.support.v4.app.FragmentActivity;
import android.os.Bundle;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.UiSettings;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class MapActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap; // Might be null if Google Play services APK is not available.
    private MapFragment mMapFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        setUpMapIfNeeded();

       /* MapFragment mapFragment = (MapFragment) getFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    */}

    @Override
    protected void onResume() {
        super.onResume();
        setUpMapIfNeeded();
    }
    @Override
    public void onMapReady(GoogleMap map) {
        // Add a marker in Sydney, Australia, and move the camera.
        map.addMarker(new MarkerOptions()
                .position(new LatLng(10, 10))
                .title("Hello world").draggable(true));
        mMap.setMyLocationEnabled(true); // false to disable
    }
    /**
     * Sets up the map if it is possible to do so (i.e., the Google Play services APK is correctly
     * installed) and the map has not already been instantiated.. This will ensure that we only ever
     * call {@link #setUpMap()} once when {@link #mMap} is not null.
     * <p/>
     * If it isn't installed {@link SupportMapFragment} (and
     * {@link com.google.android.gms.maps.MapView MapView}) will show a prompt for the user to
     * install/update the Google Play services APK on their device.
     * <p/>
     * A user can return to this FragmentActivity after following the prompt and correctly
     * installing/updating/enabling the Google Play services. Since the FragmentActivity may not
     * have been completely destroyed during this process (it is likely that it would only be
     * stopped or paused), {@link #onCreate(Bundle)} may not be called again so we should call this
     * method in {@link #onResume()} to guarantee that it will be called.
     */
    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) {
                setUpMap();
            }
        }
    }

    /**
     * This is where we can add markers or lines, add listeners or move the camera. In this case, we
     * just add a marker near Africa.
     * <p/>
     * This should only be called once and when we are sure that {@link #mMap} is not null.
     */
    private void setUpMap() {
        mMap.addMarker(new MarkerOptions().position(new LatLng(0, 0)).title("Marker"));
    }
}

Answer 1

您的 Activity 名为 MainActivity，但您尝试使用 MapActivity.this 作为 new Intent(MapActivity.this, MapActivity.class) 的第一个参数。将其更改为 MainActivity.this

startActivity(new Intent(MainActivity.this, MapActivity.class));