enter image description here当我打开Android应用程序时，它会崩溃。这是代码：
import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Build;
import android.provider.Settings;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private Button requestButton;
private TextView coordinateText;
private LocationManager locationManager;
private LocationListener locationListener;
private Button buttonMap;
private Button buttonCurrentLocation;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//reference requestButton
requestButton = (Button) findViewById(R.id.requestButton);
//reference coordText
coordinateText = (TextView) findViewById(R.id.coordinateText);
// Creating button object for buttonMap
buttonMap = (Button) findViewById(R.id.buttonMap);
//Create a button object for buttonCurrentLocation
buttonCurrentLocation = (Button) findViewById(R.id.buttonCurrentLocation);
//Action listener for buttonMap
buttonMap.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent1 = new Intent(getApplicationContext(), MapsActivity.class);
startActivity(intent1);
}
});
// Action listener for buttonCurrentLocation
buttonCurrentLocation.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), GPSShow.class);
startActivity(i);
}
});
//Initialize locationManager
locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
//Initialize locationListener
locationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
coordinateText.append("\n" + location.getLatitude() + " " + location.getLongitude());
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
Intent intent2 = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent2);
}
};
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
requestPermissions(new String[]{
Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.INTERNET
}, 10);
}
return;
} else {
configureButton();
}
}
//OUTSIDE ONCREATE METHOD
public void onRequestPermissionResult(int requestCode, String[] permissions, int[] grantResults) {
switch (requestCode) {
case 10:
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
configureButton();
return;
}
}
private void configureButton() {
requestButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
locationManager.requestLocationUpdates("gps", 5000, 0, locationListener);
}
});
}
}
这是logcat：
01-15 17:10:18.088 2340-2340/com.example.matt.palt E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.matt.palt, PID: 2340
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.matt.palt/com.example.matt.palt.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.matt.palt.MainActivity.configureButton(MainActivity.java:124)
at com.example.matt.palt.MainActivity.onCreate(MainActivity.java:103)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-15 17:10:20.435 2340-2340/com.example.matt.palt I/Process: Sending signal. PID: 2340 SIG: 9
我第一次运行应用程序时运行正常。
似乎问题是requestButton。我已经尝试进一步寻找解决方案，但找不到一个。
答案 0 :(得分：0)
找不到R.id.buttonMap，导致findViewById（R.id.buttonMap）为null。
id buttonMap应该在您的activity_main xml文件中。事实并非如此。
答案 1 :(得分：0)
从logcat中可以看出按钮requestButton为空。似乎你的java代码是正确的，问题出在你的布局中。您的xml文件中的标识requestButton并不完全相同。将您的xml与java代码匹配
