NullPointerException,是啥导致我的错误?
Posted
技术标签:
【中文标题】NullPointerException,是啥导致我的错误?【英文标题】:NullPointerException, what is causing my error?NullPointerException,是什么导致我的错误? 【发布时间】:2015-03-04 17:22:22 【问题描述】:Logcat 在 Records.java 的第 42 行返回一个 nullPointerException。第 42 行说“daily_record.setText(Daily_Record_Option);”你们能看一下这段代码吗?我已经尝试解决这个问题几个小时了,但我尝试过的没有任何帮助。谢谢! Records.java
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;
public class Records extends MainActivity
public int default_int_day = 0;
public int default_int_week = 0;
static boolean daily_recieved = false;
static boolean weekly_recieved = false;
@Override
public void onCreate(Bundle savedInstanceState)
TextView daily_record = (TextView) findViewById(R.id.daily_textview);
TextView weekly_record = (TextView) findViewById(R.id.weekly_textview);
super.onCreate(savedInstanceState);
setContentView(R.layout.personal_records);
SharedPreferences sharedPrefs = getSharedPreferences("Data", Context.MODE_PRIVATE);
int Daily_Record_Option = sharedPrefs.getInt("daily", counter);
int Weekly_Record_Option = sharedPrefs.getInt("weekly", counter_weekly);
if(isSavedDaily)
if(Daily_Record_Option > default_int_day)
daily_record.setText(Daily_Record_Option);
default_int_day = Daily_Record_Option;
daily_recieved = true;
else if(default_int_day > Daily_Record_Option)
daily_record.setText(default_int_day);
daily_recieved = false;
else
daily_record.setText("No records yet!");
else
Toast.makeText(this, "No daily data saved yet", Toast.LENGTH_LONG).show();
if(isSavedWeekly)
if(Weekly_Record_Option > default_int_week)
weekly_record.setText(Weekly_Record_Option);
default_int_week = Weekly_Record_Option;
weekly_recieved = true;
else if(default_int_week > Weekly_Record_Option)
weekly_record.setText(default_int_week);
weekly_recieved = false;
else
Toast.makeText(this, "No weekly data saved yet", Toast.LENGTH_LONG).show();
@Override
public boolean onCreateOptionsMenu(Menu menu)
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.records_menu, 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.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.Back)
Intent records_intent = new Intent(this, MainActivity.class);
startActivity(records_intent);
return true;
return super.onOptionsItemSelected(item);
还有布局文件: personal_records.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_ android:layout_
android:background="#FF8B00"
android:id="@+id/Personal_Records">
<TextView
android:layout_
android:layout_
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="@string/Your_Records"
android:id="@+id/textView5"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_margin="40dp"
android:layout_centerHorizontal="true"
android:gravity="center_horizontal"/>
<TextView
android:layout_
android:layout_
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="@string/Weekly_Record"
android:id="@+id/textView6"
android:layout_below="@+id/textView5"
android:layout_alignLeft="@+id/textView5"
android:layout_alignStart="@+id/textView5"
android:layout_marginBottom="20dp" />
<TextView
android:layout_
android:layout_
android:id="@+id/weekly_textview"
android:layout_below="@+id/textView6"
android:layout_alignLeft="@+id/textView6"
android:textAppearance="?android:attr/textAppearanceLarge"
android:layout_alignStart="@+id/textView6"
android:gravity="center_horizontal"
android:text="\@null"/>
<TextView
android:layout_
android:layout_
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="@string/Daily_Record"
android:id="@+id/textView7"
android:layout_below="@+id/weekly_textview"
android:layout_alignLeft="@+id/textView5"
android:layout_alignStart="@+id/textView5"
android:layout_marginBottom="20dp"
android:paddingTop="20dp"/>
<TextView
android:layout_
android:layout_
android:id="@+id/daily_textview"
android:layout_below="@+id/textView7"
android:textAppearance="?android:attr/textAppearanceLarge"
android:layout_alignLeft="@+id/textView6"
android:layout_alignStart="@+id/textView6"
android:text="\@null"
android:gravity="center_horizontal"/>
</RelativeLayout
还有日志猫:
java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2359)
at android.app.ActivityThread.access$700(ActivityThread.java:165)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1326)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5455)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at haveabeer.two.padc.haveabeer.Records.onCreate(Records.java:43)
//Here ^^^
at android.app.Activity.performCreate(Activity.java:5372)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
第 43 行说:“daily_record.setText(Daily_Record_Option);” 现在是第 43 行,因为我在顶部移动了一些东西。但是引发错误的区域在同一区域内/附近。
MainActivity.java
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
import java.util.Calendar;
public class MainActivity extends ActionBarActivity
public int counter = 0;
public int counter_weekly = 0;
Calendar daily_calender = Calendar.getInstance();
int hour = daily_calender.get(Calendar.HOUR);
int second = daily_calender.get(Calendar.SECOND);
int minute = daily_calender.get(Calendar.MINUTE);
int day = daily_calender.get(Calendar.DAY_OF_WEEK);
public boolean isSavedDaily = true;
public boolean isSavedWeekly = false;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageButton beer = (ImageButton) findViewById(R.id.imageButton);
SharedPreferences sharedPrefs = getSharedPreferences("Data",Context.MODE_PRIVATE);
counter = sharedPrefs.getInt("daily", counter);
counter_weekly = sharedPrefs.getInt("weekly", counter_weekly);
TextView beer_count_onLoad = (TextView) findViewById(R.id.textView);
beer_count_onLoad.setText(getResources().getString(R.string.beerCount) + "" + counter);
TextView beer_week_count_onLoad = (TextView) findViewById(R.id.textView2);
beer_week_count_onLoad.setText(getResources().getString(R.string.beerWeek) + "" + counter_weekly);
final TextView beer_count = (TextView) findViewById(R.id.textView);
final TextView beer_week = (TextView) findViewById(R.id.textView2);
beer.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
counter++;
counter_weekly++;
beer_count.setText(getResources().getString(R.string.beerCount) + "" + counter );
beer_week.setText(getResources().getString(R.string.beerWeek) + "" + counter_weekly );
);
ResetVariablesTimers();
private void ResetVariablesTimers()
SharedPreferences sharedPrefs = getSharedPreferences("Data",Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPrefs.edit();
if(hour == 0 && second == 0 && minute == 0 )
TextView reset_notification = (TextView)findViewById(R.id.textView3);
reset_notification.setText("Daily was reset to 0, was at 400");
editor.putInt("daily", counter);
editor.commit();
isSavedDaily=true;
ResetVariables();
else
Toast.makeText(this, "Not time of the day yet", Toast.LENGTH_LONG).show();
isSavedDaily=true;
if(day == 2 && second == 0 && minute == 0 && hour == 0 )
TextView reset_notification_weekly = (TextView) findViewById(R.id.textView4);
reset_notification_weekly.setText("Weekly was reset to 0, was at 400");
editor.putInt("weekly", counter_weekly);
editor.commit();
isSavedWeekly=true;
ResetVariables();
else
Toast.makeText(this, "Not time of the month yet", Toast.LENGTH_LONG).show();
isSavedWeekly=false;
public void ResetVariables()
if(Records.daily_recieved = true)
counter = 0;
if(Records.weekly_recieved = true)
counter_weekly = 0;
@Override
public boolean onCreateOptionsMenu(Menu menu)
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
@Override
public boolean onOptionsItemSelected(MenuItem item)
SharedPreferences sharedPrefs = getSharedPreferences("Data", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPrefs.edit();
editor.putInt("daily", counter);
editor.putInt("weekly", counter_weekly);
editor.commit();
// 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.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings)
return true;
else if (id == R.id.Personal_Records && isSavedDaily)
Intent records_intent = new Intent(this, Records.class);
startActivity(records_intent);
return true;
else
Toast.makeText(this, "No records available yet!", Toast.LENGTH_LONG).show();
return super.onOptionsItemSelected(item);
@Override
protected void onSaveInstanceState(Bundle outState)
SharedPreferences sharedPrefs = getSharedPreferences("Data", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPrefs.edit();
editor.putInt("daily", counter);
editor.putInt("weekly", counter_weekly);
editor.commit();
super.onSaveInstanceState(outState);
outState.putInt("daily_counter", counter);
outState.putInt("weekly_counter", counter_weekly);
ResetVariablesTimers();
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState)
super.onRestoreInstanceState(savedInstanceState);
counter = savedInstanceState.getInt("daily_counter");
counter_weekly = savedInstanceState.getInt("weekly_counter");
TextView daily = (TextView) findViewById(R.id.textView);
daily.setText(getResources().getString(R.string.beerCount) + counter);
TextView weekly = (TextView) findViewById(R.id.textView2);
weekly.setText(getResources().getString(R.string.beerWeek) + counter);
@Override
protected void onDestroy()
SharedPreferences sharedPrefs = getSharedPreferences("Data", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPrefs.edit();
editor.putInt("daily", counter);
editor.putInt("weekly", counter_weekly);
editor.commit();
super.onDestroy();
ResetVariablesTimers();
@Override
protected void onStop()
SharedPreferences sharedPrefs = getSharedPreferences("Data", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPrefs.edit();
editor.putInt("daily", counter);
editor.putInt("weekly", counter_weekly);
editor.commit();
ResetVariablesTimers();
super.onStop();
您能否就如何使 ResetVariableTimers() 变得更好提出您的想法?我想要做的是在新的一天/一周到来时重置每日和每周计数器。我在想这可能应该是一个后台服务,但我不知道该去哪里。
【问题讨论】:
尝试将daily_record.setText(Daily_Record_Option);
换成daily_record.setText(Daily_Record_Option + "");
@Rohit5k2 不,那没用。
你正在扩展MainActivity
;那里可能有问题。这个类似乎没有任何错误,除了你不应该像你正在做的那样在setText
方法中使用整数。在setText
中使用整数具有完全不同的含义。
我删除了扩展 MainActivity 并且到处都有错误。所以为了解决这个问题,我显然按下了 ALT+ENTER 来查看 Android Studio 的建议,但这没有帮助。在我的其他一项活动中,我在 setText 中使用了一个 int,它运行良好。所以我完全不知道还有什么可以尝试的。
@Rohit5k2 您是否认为问题可能源于当用户单击右上角名为“Your Records”的 ActionBar 项时启动 Records.java 活动这一事实?那是一个片段吗?
【参考方案1】:
您正在尝试获取您的TextView
而不在活动中设置内容。
将这些行放在setContentView(R.layout.personal_records);
之后
TextView daily_record = (TextView) findViewById(R.id.daily_textview);
TextView weekly_record = (TextView) findViewById(R.id.weekly_textview);
另外,你不应该在setText
中使用整数;它具有完全不同的含义。如果您这样做,它将寻找具有该整数值的资源。
【讨论】:
【参考方案2】:在引用其中的任何元素之前,您首先需要扩充您的视图。当时你有这两行代码,
TextView daily_record = (TextView) findViewById(R.id.daily_textview);
TextView weekly_record = (TextView) findViewById(R.id.weekly_textview);
您的视图仍然为空,因此出现 NullPointer 异常。在引用任何元素之前,您应该首先调用 setContentView(R.layout.myView)。
【讨论】:
我刚刚这样做了,我仍然得到 nullPointerException。 你需要将super.onCreate(savedInstanceState); setContentView(R.layout.personal_records);
移动到@Override public void onCreate(Bundle savedInstanceState)
之后的右边
你能告诉我第 42 行对应的是什么吗?您能否发布堆栈跟踪。以上是关于NullPointerException,是啥导致我的错误?的主要内容,如果未能解决你的问题,请参考以下文章
java.lang.NullPointerException错误是啥意思
为啥@ManyToMany 会导致 NullPointerException?
ProGuard 导致 NullPointerException
textout.getText() 导致“可能产生'java.lang.NullPointerException'”消息