Question

我的应用程序中有四个片段。第一个获取GPS数据用于计算速度，工作正常。一旦应用程序获取gps数据并移动到其他片段，它就会崩溃。仅供参考，其他片段都没有任何代码。

这是我的MainActivity类：

package ir.helpx.speedx;

import android.Manifest;
import android.content.pm.ActivityInfo;
import android.content.pm.PackageManager;
import android.os.Build;
import android.support.design.widget.TabLayout;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.WindowManager;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    Toolbar toolbar;
    TabLayout tabLayout;
    ViewPager viewPager;
    ViewPagerAdapter viewPagerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar =(Toolbar)findViewById(R.id.toolBar);
        setSupportActionBar(toolbar);
        tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        viewPager = (ViewPager) findViewById(R.id.viewPager);
        viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
        viewPagerAdapter.addFragments(new HomeFragment(), "Home");
        viewPagerAdapter.addFragments(new CompassFragment(), "Compass");
        viewPagerAdapter.addFragments(new HUDFragment(), "HUD");
        viewPager.setAdapter(viewPagerAdapter);
        tabLayout.setupWithViewPager(viewPager);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setRequestedOrientation (ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);


        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION}, 1);


    }


    }
    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {

        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Toast.makeText(this,"GPS permission granted", Toast.LENGTH_LONG).show();

                    //  get Location from your device by some method or code

                } else {
                    // show user that permission was denied. inactive the location based feature or force user to close the app
                }
                break;
        }
    }
}

和我的MainActivity XML：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout

    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="ir.helpx.speedx.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_height="wrap_content"
        android:layout_width="368dp"
        tools:layout_editor_absoluteY="0dp"
        tools:layout_editor_absoluteX="8dp"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <include
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            layout="@layout/toolbar_layout"
            />
        <android.support.design.widget.TabLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/tabLayout"
            app:tabMode="fixed"
            app:tabGravity="fill"
         ></android.support.design.widget.TabLayout>
        <android.support.v4.view.ViewPager
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/viewPager"
            ></android.support.v4.view.ViewPager>


    </android.support.design.widget.AppBarLayout>

</android.support.constraint.ConstraintLayout>

这是我的第一个名为Home的片段：

package ir.helpx.speedx;


import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;


/**
 * A simple {@link Fragment} subclass.
 */
public class HomeFragment extends Fragment implements LocationListener{


    public HomeFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        LocationManager mgr;
        mgr = (LocationManager)getContext().getSystemService(getActivity().LOCATION_SERVICE);
        mgr.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
        this.onLocationChanged(null);
        return inflater.inflate(R.layout.fragment_home, container, false);
    }

    //TextView msg1;

    @Override
    public void onLocationChanged(Location location) {

        if (location==null){
        TextView currentSpeed = null;

        }
        else {
            float nCurrentSpeed = location.getSpeed();
            TextView currentSpeed = (TextView) getView().findViewById(R.id.speed);
            currentSpeed.setText((int)nCurrentSpeed*18/5+"");
            //msg1=currentSpeed;
            Toast.makeText(getActivity(), "Location Found!", Toast.LENGTH_LONG).show();
        }
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }
}

这是相关的XML

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="ir.helpx.speedx.HomeFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/speed"
        android:gravity="center"
        android:textSize="180sp"
        android:textStyle="bold"
        android:textColor="@android:color/white"
        android:id="@+id/speed"/>

</FrameLayout>

这是我的第二个片段：

package ir.helpx.speedx;


import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 */
public class HUDFragment extends Fragment {


    public HUDFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_hud, container, false);
    }

}

其余片段与

类似

我有一个工具栏XML：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:minWidth="?attr/actionBarSize"
    android:fitsSystemWindows="true"
    android:id="@+id/toolBar"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    >

</android.support.v7.widget.Toolbar>

最后是我的ViewPagerAdapter：

package ir.helpx.speedx;

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 java.util.ArrayList;

/**
 * Created by abe on 5/29/2017.
 */

public class ViewPagerAdapter extends FragmentPagerAdapter {

    ArrayList<Fragment> fragments = new ArrayList<>();
    ArrayList<String> tabTitles = new ArrayList<>();

    public void addFragments(Fragment fragments, String titles){
        this.fragments.add(fragments);
        this.tabTitles.add(titles);
    }


    public ViewPagerAdapter(FragmentManager fm){
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return fragments.get(position);
    }

    @Override
    public int getCount() {
        return fragments.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles.get(position);
    }
}

请帮帮我！谢谢

Answer 1

我想我可以通过添加

来解决这个问题

＆＃13;

viewPager.setOffscreenPageLimit(4);

＆＃13;

到我的MainActivity。我认为这是因为默认情况下，ViewPager在空闲状态下仅保留视图层次结构中的一个页面。如果我做对了，请告诉我！

当我从一个片段移动到另一个片段时应用程序崩溃

1 个答案: