android - 对 ViewPager 的多个选项卡布局使用单个片段类
问题描述
在 TabsDemoApp 我尝试使用一个片段并在三个 XML 布局之间切换,我看到了这些问题
“如何知道 onCreateView 函数中哪个选项卡处于活动状态?”
我试图理解它并将其应用于此示例
这是完整的代码
选项卡布局适配器
package com.example.tabsdemoapp;
import java.util.ArrayList;
import java.util.List;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;
public class TabLayoutAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public TabLayoutAdapter(@NonNull FragmentManager fm, int mNumOfTabs) {
super(fm, mNumOfTabs);
this.mNumOfTabs = mNumOfTabs;
}
@NonNull
@Override
public Fragment getItem(int position) {
return TabFragment.newInstance(position);
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
标签片段
package com.example.tabsdemoapp;
import android.content.Context;
import android.os.Bundle;
import android.provider.SyncStateContract;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
public class TabFragment extends Fragment {
private static String ARG_POSITION = "position";
private static int fragmentId = 0;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
if(container.getId() == R.id.tab1) {
return inflater.inflate(R.layout.tab1, container, false);
}else if(container.getId() == R.id.tab2){
return inflater.inflate(R.layout.tab2, container, false);
}else {
return inflater.inflate(R.layout.tab3, container, false);
}
}
public static TabFragment newInstance(int position) {
TabFragment fragment = new TabFragment();
Bundle bundle = new Bundle();
bundle.putInt(ARG_POSITION, position);
fragment.setArguments(bundle);
return fragment;
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
fragmentId = getArguments().getInt(ARG_POSITION,fragmentId);
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
assert getTargetFragment() != null;
getChildFragmentManager().beginTransaction().
replace(R.id.container, getTargetFragment()).
commit();
}
@Override
public void onAttach(@NonNull Context context) {
super.onAttach(context);
}
@Override
public void onDetach() {
super.onDetach();
}
}
main_activity.xml
<LinearLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/rootView"
tools:context=".MainActivity">
<com.google.android.material.tabs.TabLayout
android:id="@+id/myTabLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:layout_editor_absoluteX="1dp"
tools:layout_editor_absoluteY="186dp">
</com.google.android.material.tabs.TabLayout>
<androidx.viewpager.widget.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/viewPager"
app:elevation="5dp"
>
</androidx.viewpager.widget.ViewPager>
</LinearLayout>
MainActivity 类
public class MainActivity extends AppCompatActivity {
TabLayout tabLayout;
ViewPager viewPager;
TabLayoutAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabLayout = findViewById(R.id.myTabLayout);
viewPager = findViewById(R.id.viewPager);
tabLayout.setupWithViewPager(viewPager);
adapter = new TabLayoutAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapter);
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
switch (tab.getPosition()) {
case 0:
viewPager.setCurrentItem(tab.getPosition());
break;
case 1:
viewPager.setCurrentItem(tab.getPosition());
break;
case 2:
viewPager.setCurrentItem(tab.getPosition());
break;
default:
viewPager.setCurrentItem(tab.getPosition());
}
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
}
每个选项卡都有一个三个 XML,tab1,tab2,tab3
tab1.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/tab1"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Tab one"
android:textAppearance="?android:attr/textAppearanceLarge"/>
</RelativeLayout>
tab2.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/tab2"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Tab two"
android:textAppearance="?android:attr/textAppearanceLarge"/>
</RelativeLayout>
tab3.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/tab3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Tab three"
android:textAppearance="?android:attr/textAppearanceLarge"/>
</RelativeLayout>
运行应用程序后,我看到一个空白页面,没有 ViewPager 和 TabLayout
解决方案
- 为 TabLayout 制作标题,您
TabLayoutAdapter
应该覆盖getPageTitle
@Override
public CharSequence getPageTitle(int position) {
return "Tab " + position;
}
- 你错在这里
container
传给onCreateView
永远是"@+id/viewPager"
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
if(container.getId() == R.id.tab1) {
return inflater.inflate(R.layout.tab1, container, false);
}else if(container.getId() == R.id.tab2){
return inflater.inflate(R.layout.tab2, container, false);
}else {
return inflater.inflate(R.layout.tab3, container, false);
}
}
将此代码更改为
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
if(fragmentId == 0) {
return inflater.inflate(R.layout.tab1, container, false);
}else if(fragmentId == 1){
return inflater.inflate(R.layout.tab2, container, false);
}else {
return inflater.inflate(R.layout.tab3, container, false);
}
}
TabLayoutAdapter
通过总片段而不是通过初始化,tabLayout.getTabCount()
因为现在 tabLayout 没有子选项卡,它将返回 0。
adapter = new TabLayoutAdapter(getSupportFragmentManager(), 3);
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