【发布时间】：2018-06-15 22:28:51
【问题描述】：
我是编程新手，在互联网上找不到任何理想的解决方案，因此希望您能帮助我。
我想编写一个应用程序，它有 4 个选项卡，每个选项卡都有一个 ListView。如果我创建一个只有 4 个选项卡或只有 ListView 的应用程序，它工作得非常好。然而，当涉及到结合这两个部分时，它不起作用。启动应用程序时它开始崩溃。
请看一下我的代码。我将只显示一个选项卡 java 和 xml 代码，因为它们总是相同的。
感谢您抽出宝贵时间。
MainActivity.java
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity {
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/main_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.matrix.koks.MainActivity">
<android.support.design.widget.AppBarLayout
android:id="@+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="@dimen/appbar_padding_top"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:layout_weight="1"
android:background="?attr/colorPrimary"
app:layout_scrollFlags="scroll|enterAlways"
app:popupTheme="@style/AppTheme.PopupOverlay"
app:title="@string/app_name">
</android.support.v7.widget.Toolbar>
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.design.widget.TabItem
android:id="@+id/tabItem"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/tab_text_1" />
<android.support.design.widget.TabItem
android:id="@+id/tabItem2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/tab_text_2" />
<android.support.design.widget.TabItem
android:id="@+id/tabItem3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/tab_text_3" />
<android.support.design.widget.TabItem
android:id="@+id/tabItem4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/tab_text_4" />
</android.support.design.widget.TabLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>
Tab1.java
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import java.util.ArrayList;
public class Tab1 extends Fragment {
EditText EditText;
Button AddBtn;
Button SubBtn;
Button ResultBtn;
Button ResetButton;
ListView ListView;
ArrayList<String> ArrayListString;
ArrayAdapter<String> Adapter;
ArrayList<Integer> ArrayListInteger;
int Value;
int Count;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_1, container, false);
EditText = (EditText) getView().findViewById(R.id.EnterValueEditText1);
AddBtn = (Button) getView().findViewById(R.id.AddDataButton1);
SubBtn = (Button) getView().findViewById(R.id.SubDataButton1);
ResultBtn = (Button) getView().findViewById(R.id.ResultButton1);
ResetButton = (Button) getView().findViewById(R.id.ResetButton1);
ListView = (ListView) getView().findViewById(R.id.ListView1);
ArrayListString = new ArrayList<String>();
Adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, ArrayListString);
ArrayListInteger = new ArrayList<Integer>();
ListView.setAdapter(Adapter);
AddBtnClick();
SubBtnClick();
ResultButtonClick();
ResetButtonClick();
return rootView;
}
public void AddBtnClick(){
AddBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String Number = EditText.getText().toString();
ArrayListString.add(Number);
Adapter.notifyDataSetChanged();
Value = Integer.parseInt(EditText.getText().toString());
Count += Value;
EditText.getText().clear();
}
});
}
public void SubBtnClick(){
SubBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String Number = EditText.getText().toString();
ArrayListString.add(Number);
Adapter.notifyDataSetChanged();
Value = Integer.parseInt(EditText.getText().toString());
Count -= Value;
EditText.getText().clear();
}
});
}
public void ResultButtonClick(){
ResultBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ArrayListString.clear();
Adapter.notifyDataSetChanged();
String Final = String.valueOf(Count);
ArrayListString.add(Final);
Adapter.notifyDataSetChanged();
}
});
}
public void ResetButtonClick(){
ResetButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
ArrayListString.clear();
Adapter.notifyDataSetChanged();
Count = 0;
}
});
}
}
fragment_1.xml
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/constraintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="@+id/EnterValueEditText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="@string/EditText"
android:inputType="number"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/AddDataButton1"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="@string/AddData"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.275"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/EnterValueEditText1" />
<Button
android:id="@+id/SubDataButton1"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="@string/SubData"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.725"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/EnterValueEditText1" />
<Button
android:id="@+id/ResultButton1"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="16dp"
android:text="@string/Result"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.275"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/AddDataButton1" />
<Button
android:id="@+id/ResetButton1"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="16dp"
android:text="@string/Reset"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.725"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/SubDataButton1" />
<ListView
android:id="@+id/ListView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
app:layout_constraintTop_toBottomOf="@+id/ResultButton1" />
</android.support.constraint.ConstraintLayout>
Logcat
06-16 11:29:37.227 2486-2486/com.matrix.koks I/art: Not late-enabling -Xcheck:jni (already on)
06-16 11:29:37.227 2486-2486/com.matrix.koks W/art: Unexpected CPU variant for X86 using defaults: x86
06-16 11:29:37.321 2486-2486/com.matrix.koks W/System: ClassLoader referenced unknown path: /data/app/com.matrix.koks-2/lib/x86
06-16 11:29:37.334 2486-2486/com.matrix.koks I/InstantRun: starting instant run server: is main process
06-16 11:29:37.389 2486-2486/com.matrix.koks W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
06-16 11:29:40.501 2486-2486/com.matrix.koks D/AndroidRuntime: Shutting down VM
--------- beginning of crash
06-16 11:29:40.553 2486-2486/com.matrix.koks E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.matrix.koks, PID: 2486
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.matrix.koks.Tab1.onCreateView(Tab1.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2346)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1428)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1759)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1827)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:797)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2596)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2383)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2338)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2215)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:649)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:145)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1238)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1086)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1616)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:739)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:91)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1361)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:809)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:141)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
at android.view.View.measure(View.java:19857)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689)
at android.view.View.measure(View.java:19857)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1619)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
at android.view.Choreographer.doCallbacks(Choreographer.java:686)
at android.view.Choreographer.doFrame(Choreographer.java:621)
06-16 11:29:40.553 2486-2486/com.matrix.koks E/AndroidRuntime: at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
【问题讨论】：
标签： java android listview android-fragments