Android 使用 LocationListener 和 LocationManager 的工作室项目似乎没有 运行

Question

我编写并编译了下面的程序，运行 但是我从 运行 它在我的 phone 上。 有两个位置输出变量，speed 和 ourSpe，因为 ourSpe 来自我观看的一个 youtube 视频，但它不起作用，而 speed 来自堆栈溢出问题我抬头看了看。两者都有帮助，但都没有得到打印出来的结果我按下按钮 spedButt。我想我只是按错误的顺序编写了代码，但我也不确定我是否在使用 LocationManager 正确。

布局文件在 Relativelayout 中只有两个 textViews 和一个 Button，但堆栈溢出一直给我一个错误，我也想不出那个。我今天过得很糟糕。

主要代码

    package com.example.vitaliy_2.safespeedalert;

    import android.Manifest;
    import android.content.Context;
    import android.content.pm.PackageManager;
    import android.location.Location;
    import android.location.LocationListener;
    import android.location.LocationManager;
    import android.os.Bundle;
    import android.support.v4.app.ActivityCompat;
    import android.support.v7.app.AppCompatActivity;
    import android.view.View;
    import android.widget.Button;
    import android.widget.TextView;



    public class SpeedTest extends AppCompatActivity implements LocationListener {
            TextView txt;
            TextView txt_2;
            Button spedButt;
            float curSpe;
            float speed;
            Location l;
            Location mLastLocation;
            Location pCurrentLocation;

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



         txt = (TextView) findViewById(R.id.speed_display);
            txt_2 = (TextView) findViewById(R.id.speed_display_2);
            spedButt = (Button) findViewById(R.id.spedButt);
            speed = 0;

        LocationManager lm = (LocationManager)this.getSystemService(Context.LOCATION_SERVICE);

            if (ActivityCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)!= PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_COARSE_LOCATION) !=PackageManager.PERMISSION_GRANTED) {return;}
            lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
            this.onLocationChanged(null);

        }



        @Override
        public void onLocationChanged(final Location location) {
            l = location;
            if (this.mLastLocation != null)
                speed = (float )Math.sqrt(
                        Math.pow(pCurrentLocation.getLongitude() - mLastLocation.getLongitude(), 2)
                                + Math.pow(pCurrentLocation.getLatitude() - mLastLocation.getLatitude(), 2)
                ) / (pCurrentLocation.getTime() - this.mLastLocation.getTime());
            this.mLastLocation = pCurrentLocation;



            spedButt.setOnClickListener(new View.OnClickListener(){
                @Override
                public void onClick(View v) {
                    if(l == null){
                        txt.setText("-.- m/s");
                        txt_2.setText("-.- m/s");

                    }else{
                        if (pCurrentLocation.hasSpeed())


   speed = pCurrentLocation.getSpeed();
                    curSpe = location.getSpeed();

                    String sent = speed + "m/s";
                    txt.setText(sent);
                    String sentTwo = curSpe + "m/s";
                    txt_2.setText(sentTwo);
                }
            }
        });

    }

Answer 1

回答我自己的问题，这段代码自动弹出，但仍然需要一个请求权限的子句。

if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
            != PackageManager.PERMISSION_GRANTED) {


        ActivityCompat.requestPermissions(this,
                new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);


        return;
    }else{
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 5000, 0, this);
    }
    this.onLocationChanged(null);