android - toast 不起作用

Question

所以我只是想获取用户的位置并在 toast 中显示它...但它根本不起作用...我也尝试在 Activity 开始时显示 toast 但即使在那个时候它也不起作用这是我的代码

package com.example.alert;

import com.example.alert.CurrentLocation.MyLocationListener;

import android.app.Activity;
import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;


public class ViewAlerters extends Activity{

private Button addButton;
private Button removeButton;
LocationManager lm=(LocationManager)getSystemService(Context.LOCATION_SERVICE);

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.view_alerters);
    Toast.makeText( ViewAlerters.this,"Hello",Toast.LENGTH_SHORT).show();

    LocationListener ll=new MyLocationListener();
    //lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 5*60*10000, 0, ll);
    lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0, 0, ll);
    setUpViews();

}

private void setUpViews() {
    Toast.makeText( getApplicationContext(),"Hello",Toast.LENGTH_SHORT).show();

    addButton = (Button) findViewById(R.id.add_button);
    //alerterText = (TextView) findViewById(R.id.alert_list_text);
    removeButton = (Button)findViewById(R.id.remove_button);
    addButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Intent intent = new Intent(ViewAlerters.this,AddAlerter.class);
            startActivity(intent);
        }
    });

}



/* Class My Location Listener */
public class MyLocationListener implements LocationListener
{

    public void onLocationChanged(Location loc)
    {
        if(loc!=null)
        {
            double x;


            String Text = "My current location is: " +"Latitud = " + loc.getLatitude() +"Longitud = " + loc.getLongitude();
        /*  cr.moveToFirst();
            while(!cr.isAfterLast()) {
                 al.add(cr.getString(cr.getColumnIndex(dbAdapter.KEY_NAME))); //add the item
                 cr.moveToNext();
            }*/
        //  lm.addProximityAlert(loc.getLatitude(), loc.getLongitude(), 10009,, intent)

            //for loop, alerters retrieving one by one
//      x= calcDistance(loc.getLatitude(),loc.getLongitude(),z,y);
    //      if(x<1){
        //        Intent myIntent = new Intent(ViewAlerters.this,CallMode.class);
          //        startActivity(myIntent);
            }

        }

    public void onProviderDisabled(String provider) {
        // TODO Auto-generated method stub
        Toast.makeText( getApplicationContext(),"Gps Disabled - @From :Alert Me",Toast.LENGTH_SHORT ).show();


    }

    public void onProviderEnabled(String provider) {
        // TODO Auto-generated method stub
        Toast.makeText( getApplicationContext(),"Gps Enabled - @From :Alert Me",Toast.LENGTH_SHORT).show();

    }

    public void onStatusChanged(String provider, int status, Bundle extras) {
        // TODO Auto-generated method stub

    }
    }


public double calcDistance(double latA, double longA, double latB, double longB) {

    double theDistance = (Math.sin(Math.toRadians(latA)) *  Math.sin(Math.toRadians(latB)) + Math.cos(Math.toRadians(latA)) * Math.cos(Math.toRadians(latB)) * Math.cos(Math.toRadians(longA - longB)));
    return new Double((Math.toDegrees(Math.acos(theDistance))) * 69.09*1.6093);
}

Answer 1

不要使用 getApplicationContext:

Toast.makeText( this,"Hello",Toast.LENGTH_SHORT).show();

请引用这个关于Context 差异的问题:difference and when to use getApplication(), getApplicationContext(), getBaseContext() and someClass.this