我是一个安卓的Android应用程序制造商，以下是我的第一个应用程序。 该应用程序基本上做的是它获取手机的位置，延迟5秒，并运行另一个getLocation;然后它从这两点得出速度，并指出用户是否在使用手机时走路。
Studio中的代码没有问题，但是当我尝试运行我的应用程序时，手机只是说“应用程序停止了”＃39;它关闭了应用程序。 我花了几个小时试图搞清楚，但无济于事。
我做错了什么？
package com.example.denny.myapplication;
import android.Manifest.permission;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationManager;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.provider.Settings;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
PackageManager pm = getPackageManager();
if (pm.checkPermission(permission.ACCESS_FINE_LOCATION, getPackageName()) == PackageManager.PERMISSION_DENIED) {
alertboxGPS();
}
mHandler = new Handler();
startRepeatingTask();
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
}
);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
//Also, chuck the subroutine settings here. :3
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
PackageManager pm = getPackageManager();
protected void alertboxGPS() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Your Device's GPS is Disabled")
.setCancelable(true)
.setTitle("** Gps Status **")
.setPositiveButton("Gps On",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// finish the current activity
// AlertBoxAdvance.this.finish();
Intent myIntent = new Intent(
Settings.ACTION_SECURITY_SETTINGS);
startActivity(myIntent);
dialog.cancel();
}
})
.setNegativeButton("Cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// cancel the dialog box
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}
protected void alertboxViolation() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Please stop walking. You may get in an accident.")
.setCancelable(false)
.setTitle("Walking Warning")
.setPositiveButton("Stop Walking",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// finish the current activity
// AlertBoxAdvance.this.finish();
Intent myIntent = new Intent(
Settings.ACTION_SECURITY_SETTINGS);
startActivity(myIntent);
dialog.cancel();
}
})
.setNegativeButton("Cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// cancel the dialog box
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}
//Some Default Integers
int ViolationLimit = 10;
int SpeedLimit = 100;
int ExceedInstance = 0;
//Default Value
LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Location location1;
Location location2;
private double GetSpeed(Location location1, Location location2) {
if (location1 == null) {
location1 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
location2 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
} else {
location1 = location2;
if (checkSelfPermission(permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
}
location2 = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
}
double Distance;
Distance = location1.distanceTo(location2);
double Speed = Distance / mInterval;
return Speed;
}
private int Judge(double Speed, int ViolationLimit, int SpeedLimit, int ExceedInstance) {
if (Speed >= 1 && Speed <= SpeedLimit) {
ExceedInstance += 1;
}
if (ExceedInstance >= ViolationLimit) {
alertboxViolation();
}
return ExceedInstance;
}
void stopRepeatingTask() {
mHandler.removeCallbacks(mStatusChecker);
}
private int mInterval = 3000; // 3 seconds by default, can be changed later
private Handler mHandler;
Runnable mStatusChecker = new Runnable() {
@Override
public void run() {
updateStatus();
mHandler.postDelayed(mStatusChecker, mInterval);
}
};
private void updateStatus() {
//Is used for updating mInterval
}
void startRepeatingTask() {
double Speed = GetSpeed(location1, location2);
Judge(Speed, ViolationLimit, SpeedLimit, ExceedInstance);
mStatusChecker.run();
}
}
Logcat日志：
10-13 23:23:55.818 13410-13410/? E/SELinux: Function: selinux_android_load_priority [0], There is no sepolicy file
10-13 23:23:55.818 13410-13410/? E/SELinux:
10-13 23:23:55.818 13410-13410/? E/SELinux: Function: selinux_android_load_priority , loading version is VE=SEPF_GT-I9505_4.3_0024
10-13 23:23:55.818 13410-13410/? E/SELinux:
10-13 23:23:55.818 13410-13410/? E/SELinux:
10-13 23:23:55.818 13410-13410/? E/SELinux: selinux_android_seapp_context_reload: seapp_contexts file is loaded from /data/security/spota/seapp_contexts
10-13 23:23:55.818 13410-13410/? D/dalvikvm: Late-enabling CheckJNI
10-13 23:23:55.928 13410-13410/com.example.denny.myapplication I/dalvikvm: Could not find method com.example.denny.myapplication.MainActivity.checkSelfPermission, referenced from method com.example.denny.myapplication.MainActivity.GetSpeed
10-13 23:23:55.928 13410-13410/com.example.denny.myapplication W/dalvikvm: VFY: unable to resolve virtual method 16261: Lcom/example/denny/myapplication/MainActivity;.checkSelfPermission (Ljava/lang/String;)I
10-13 23:23:55.928 13410-13410/com.example.denny.myapplication D/dalvikvm: VFY: replacing opcode 0x6e at 0x0028
10-13 23:23:55.938 13410-13410/com.example.denny.myapplication D/AndroidRuntime: Shutting down VM
10-13 23:23:55.938 13410-13410/com.example.denny.myapplication W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x4190e898)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.denny.myapplication/com.example.denny.myapplication.MainActivity}: java.lang.NullPointerException
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2219)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.access$700(ActivityThread.java:159)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.os.Looper.loop(Looper.java:137)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5419)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:525)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: Caused by: java.lang.NullPointerException
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.content.ContextWrapper.getPackageManager(ContextWrapper.java:94)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at com.example.denny.myapplication.MainActivity.<init>(MainActivity.java:74)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.Class.newInstanceImpl(Native Method)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.Class.newInstance(Class.java:1130)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2210)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.access$700(ActivityThread.java:159)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.os.Looper.loop(Looper.java:137)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5419)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:525)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
10-13 23:23:55.948 13410-13410/com.example.denny.myapplication E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
10-13 23:24:03.355 13410-13410/com.example.denny.myapplication I/Process: Sending signal. PID: 13410 SIG: 9
这是一个非常大的日志，但我不知道如何以更好的方式做到这一点。
声明 这个问题与Null Pointer问题不一样，因为我已经制作了一个应用程序而且我不知道是什么导致它。这就是我提出这个问题的原因。
答案 0 :(得分：2)
首先，关于你的评论：
这个问题是在问别人不知道的事情。我是一个 应用程序，我不知道为什么它会关闭。请不要假设 每个人都知道他们正在做什么的一切 问一个问题。
人们正在努力帮助你。在写这样的评论之前，你可能想重新考虑一下你的态度。
其次，@谢尔文是正确的。您的logcat输出明确指出您的应用程序崩溃是由NullPointerException（NPE）引起的：
E/AndroidRuntime: Caused by: java.lang.NullPointerException
NullPointerException是由代码中的（其他东西）错误逻辑引起的。您的代码是应用程序的一部分这一事实无关紧要。您应该阅读linked question以了解NPE是什么以及它们发生的原因。
讲座结束，让我们来看看你的问题。
Logcat为您提供了大量有关错误的信息，通常包括显示问题的原因和堆栈跟踪。所以，从顶部开始：
E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{...}: java.lang.NullPointerException
好的，在Activity实例化期间，它是一个NullPointerException。为什么呢？
Caused by: java.lang.NullPointerException
E/AndroidRuntime: at android.content.ContextWrapper.getPackageManager(ContextWrapper.java:94)
at com.example.denny.myapplication.MainActivity.<init>(MainActivity.java:74)
因此调用getPackageManager()时出现问题。 您的代码中最近的位置是MainActivity.<init>, MainActivity.java, line 74
<init>只是构建对象时的Java方法＆＃34;。
查看源代码，您试图在对象构造期间初始化PackageManager pm字段实例：
@Override
public boolean onOptionsItemSelected(MenuItem item) {
...
}
PackageManager pm = getPackageManager();
protected void alertboxGPS() {
...
}
问题是当getPackageManager()实例正在构建时正在调用Activity - 此时并不是所有内容都已就绪。
几乎可以肯定的是，对getPackageManager()的调用试图使用尚未创建的对象 - 因此NullPointerException。
一种解决方案是删除pm字段的初始化，而是在onCreate()期间设置它 - 此时，您的Activity实例将完全构建并{{1调用将成功。
更好的解决方案是完全删除getPackageManager()字段，只需在需要时创建局部变量 - 就像您在pm中所做的一样。