该应用程序是一个普通的计算器，但是顶部有选项卡（ViewPager）。代码中没有错误，但是当您启动应用程序时，无论是在Android Studio内置的模拟器还是在您自己的手机上，应用程序都立即崩溃。重新启动没有帮助。使缓存无效/也重新启动。谁不是Android Studio的新手，请告诉我我在哪里出错。
LOGCAT
2019-11-10 13:13:40.348 6986-6986/? I/ample.viewpage: Not late-enabling -Xcheck:jni (already on)
2019-11-10 13:13:40.401 6986-6986/? W/ample.viewpage: Unexpected CPU variant for X86 using defaults: x86
2019-11-10 13:13:41.080 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden method Landroid/graphics/drawable/Drawable;->getOpticalInsets()Landroid/graphics/Insets; (light greylist, linking)
2019-11-10 13:13:41.080 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden field Landroid/graphics/Insets;->left:I (light greylist, linking)
2019-11-10 13:13:41.080 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden field Landroid/graphics/Insets;->right:I (light greylist, linking)
2019-11-10 13:13:41.080 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden field Landroid/graphics/Insets;->top:I (light greylist, linking)
2019-11-10 13:13:41.081 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden field Landroid/graphics/Insets;->bottom:I (light greylist, linking)
2019-11-10 13:13:41.170 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (light greylist, reflection)
2019-11-10 13:13:41.171 6986-6986/com.example.viewpager W/ample.viewpage: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (light greylist, reflection)
2019-11-10 13:13:41.234 6986-6986/com.example.viewpager D/AndroidRuntime: Shutting down VM
2019-11-10 13:13:41.238 6986-6986/com.example.viewpager E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.viewpager, PID: 6986
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.viewpager/com.example.viewpager.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.viewpager.MainActivity.setOnclick(MainActivity.java:119)
at com.example.viewpager.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
MainActivity.java
package com.example.viewpager;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;
import android.os.Bundle;
import android.text.Editable;
import android.text.InputType;
import android.text.TextWatcher;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.TextView;
import net.objecthunter.exp4j.Expression;
import net.objecthunter.exp4j.ExpressionBuilder;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import com.google.android.material.tabs.TabLayout;
public class MainActivity extends AppCompatActivity implements Tab1.OnFragmentInteractionListener, Tab2.OnFragmentInteractionListener, Tab3.OnFragmentInteractionListener, View.OnClickListener {
private EditText inputtext;
private TextView resulttext;
private Button but0;
private Button but1;
private Button but2;
private Button but3;
private Button but4;
private Button but5;
private Button but6;
private Button but7;
private Button but8;
private Button but9;
private ImageButton butadd;
private ImageButton butmin;
private ImageButton butmulti;
private Button butdivi;
private ImageButton butdelet;
private Button butc;
private Button butbra;
private Button but100;
private Button butequl;
private Button butsing;
private Button butvir;
private boolean stateError;
private boolean isNumber;
private boolean lastDot;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
inisializeButtons();
setOnclick();
// Hiding and disable keyboard
inputtext.setRawInputType(InputType.TYPE_NULL);
inputtext.addTextChangedListener(textWatcher);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tablayout);
tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));
tabLayout.addTab(tabLayout.newTab().setText("Tab 3"));
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
final PagerAdapter adapter = new PagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapter);
viewPager.setOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
{
}
}
private void inisializeButtons() {
this.inputtext = findViewById(R.id.input);
this.resulttext = findViewById(R.id.result);
this.but0 = findViewById(R.id.but0);
this.but1 = findViewById(R.id.but1);
this.but2 = findViewById(R.id.but2);
this.but3 = findViewById(R.id.but3);
this.but4 = findViewById(R.id.but4);
this.but5 = findViewById(R.id.but5);
this.but6 = findViewById(R.id.but6);
this.but7 = findViewById(R.id.but7);
this.but8 = findViewById(R.id.but8);
this.but9 = findViewById(R.id.but9);
this.but100 = findViewById(R.id.but100);
this.butadd = findViewById(R.id.butplus);
this.butmin = findViewById(R.id.butmin);
this.butmulti = findViewById(R.id.butmult);
this.butdivi = findViewById(R.id.butdivi);
this.butdelet = findViewById(R.id.butdelet);
this.butbra = findViewById(R.id.butbra);
this.butsing = findViewById(R.id.butsin);
this.butc = findViewById(R.id.butc);
this.butequl = findViewById(R.id.butequl);
this.butvir = findViewById(R.id.butv);
}
private void setOnclick() {
this.but0.setOnClickListener(this);
this.but1.setOnClickListener(this);
this.but2.setOnClickListener(this);
this.but3.setOnClickListener(this);
this.but4.setOnClickListener(this);
this.but5.setOnClickListener(this);
this.but6.setOnClickListener(this);
this.but7.setOnClickListener(this);
this.but8.setOnClickListener(this);
this.but9.setOnClickListener(this);
this.but100.setOnClickListener(this);
this.butadd.setOnClickListener(this);
this.butmulti.setOnClickListener(this);
this.butmin.setOnClickListener(this);
this.butdelet.setOnClickListener(this);
this.butdivi.setOnClickListener(this);
this.butvir.setOnClickListener(this);
this.butequl.setOnClickListener(this);
this.butc.setOnClickListener(this);
this.butdelet.setOnClickListener(this);
this.butsing.setOnClickListener(this);
this.butbra.setOnClickListener(this);
}
@Override
public void onFragmentInteraction(Uri uri) {
}
@Override
public void onClick(View v) {
int Id = v.getId();
switch (Id) {
case R.id.but0:
append("0");
isNumber = true;
break;
case R.id.but1:
append("1");
isNumber = true;
break;
case R.id.but2:
append("2");
isNumber = true;
break;
case R.id.but3:
append("3");
isNumber = true;
break;
case R.id.but4:
append("4");
isNumber = true;
break;
case R.id.but5:
append("5");
isNumber = true;
break;
case R.id.but6:
append("6");
isNumber = true;
break;
case R.id.but7:
append("7");
isNumber = true;
break;
case R.id.but8:
append("8");
isNumber = true;
break;
case R.id.but9:
append("9");
isNumber = true;
break;
case R.id.but100:
if (!isEmpty() && isNumber)
append("%");
break;
case R.id.butplus:
if (!isEmpty())
if (endsWithOperatore())
replace("+");
else
append("+");
isNumber = false;
lastDot = false;
break;
case R.id.butmin:
if (endsWithOperatore())
replace("-");
else
append("-");
isNumber = false;
lastDot = false;
break;
case R.id.butmult:
if (!isEmpty())
if (endsWithOperatore())
replace("x");
else
append("x");
isNumber = false;
lastDot = false;
break;
case R.id.butdivi:
if (!isEmpty())
if (endsWithOperatore())
replace("/");
else
append("/");
isNumber = false;
lastDot = false;
break;
case R.id.butv:
if (isNumber && !stateError && !lastDot) {
append(".");
isNumber = false;
lastDot = true;
} else if (isEmpty()) {
append("0.");
isNumber = false;
lastDot = true;
}
break;
case R.id.butdelet:
delete();
break;
case R.id.butc:
clear();
break;
case R.id.butbra:
bracket();
break;
case R.id.butequl:
calcule(true);
break;
case R.id.butsin:
setSing();
break;
default:
break;
}
}
private void setSing() {
if (isEmpty()){
append("(-");
}else if (isNumber && !endsWithOperatore()){
int index1;
int index2;
int index3;
int index4;
int lastone = 0;
index1 = getinput().lastIndexOf("x") + 1;
index2 = getinput().lastIndexOf("+") + 1;
index3 = getinput().lastIndexOf("-") + 1;
index4 = getinput().lastIndexOf("/") + 1;
if (index1 > index2 && index1 > index3 && index1 > index4)
lastone = index1;
else if (index2 > index1 && index2 > index3 && index2 > index4)
lastone = index2;
else if (index3 > index2 && index3 > index1 && index3 > index4)
lastone = index1;
else if (index4 > index1 && index4 > index3 && index4 > index2)
lastone = index1;
char ch=getinput().charAt(lastone);
appendsing("(-" + String.valueOf(ch), lastone);
}
}
private void appendsing(String str,int index) {
inputtext.getText().replace(index,index+1,str);
}
private void bracket() {
if ((!stateError && !isEmpty() && !endsWithbra() && isNumber) || isclosed()) {
append("x(");
} else if (isEmpty() || endsWithOperatore() || endsWithbra()) {
append("(");
} else if (!isEmpty() && !endsWithbra()) {
append(")");
}
}
private boolean endsWithbra() {
return getinput().endsWith("(");
}
private boolean isclosed() {
return getinput().endsWith(")");
}
private boolean endsWithOperatore() {
return getinput().endsWith("+") || getinput().endsWith("-") || getinput().endsWith("/") || getinput().endsWith("x");
}
private void replace(String str) {
inputtext.getText().replace(getinput().length() - 1, getinput().length(), str);
}
private void clear() {
lastDot = false;
isNumber = false;
stateError = false;
inputtext.getText().clear();
}
private void append(String str) {
this.inputtext.getText().append(str);
}
private void delete() {
if (!isEmpty()) {
this.inputtext.getText().delete(getinput().length() - 1, getinput().length());
} else clear();
}
private String getinput() {
return this.inputtext.getText().toString();
}
private boolean isEmpty() {
return getinput().isEmpty();
}
private void calcule(boolean isequlclick) {
String input = getinput();
try {
if (!isEmpty() && !endsWithOperatore()) {
if (input.contains("x")) {
input = input.replaceAll("x", "*");
}
Expression expression = new ExpressionBuilder(input).build();
double result = expression.evaluate();
if (isequlclick) {
inputtext.setText(String.valueOf(result));
resulttext.setText("");
} else
resulttext.setText(String.valueOf(result));
} else resulttext.setText("");
} catch (Exception e) {
stateError = true;
isNumber = false;
}
}
TextWatcher textWatcher = new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
calcule(false);
}
@Override
public void afterTextChanged(Editable s) {
}
};
}
您的应用程序确实因错误而崩溃。您收到一个NullPointerException。 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
这意味着您正在为null的Button上设置OnClickListener。在您的initializeButtons()程序中，您可能忘记了按钮或ID拼写错误？