我按照以下链接在标签布局中添加图标： https://guides.codepath.com/android/google-play-style-tabs-using-tablayout#sliding-tabs-layout
一切正常，包括带文字的标签。当我尝试添加图标时，应用程序会在启动时崩溃。我一直在寻找超过5小时，我对android很新。 ： - （
我只在activity_main.xml中收到错误：
tools:context="com.example.android.viewpager.MainActivity"
在viewpager.MainActivity上显示带有注释的红色案例：
"Unresolved class, MainActivity --- Validates resources references inside android XML files."
但是，当切换到仅文本选项卡时，此错误仍然存在并且应用程序在该情况下运行（错误仍然存在，因此我认为这不相关）。
我将更改隔离到下面的类，在文本和图标模式之间来回切换（用相应的标题消隐行）。这似乎不是样式的问题，是的，AllCaps在＆＃34; TextAppearance.Design.tab＆＃34;
中设置为falseSimpleFragmentPagerAdapter.java：
package com.example.android.miwok;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.content.ContextCompat;
import android.text.Spannable;
import android.text.SpannableString;
import android.text.style.ImageSpan;
/**
* Provides the appropriate {@link Fragment} for a view pager.
*/
public class SimpleFragmentPagerAdapter extends FragmentPagerAdapter {
final int PAGE_COUNT = 4;
// if you work with text in the tabs
private String tabTitles[] = new String [] { "Time", "$", "Company", "A trip" };
// Always needed
private Context context;
//if you work with Icons in the tabs
/*
private int[] imageResId = {
R.drawable.ic_access_time_white_24dp,
R.drawable.ic_attach_money_white_24dp,
R.drawable.ic_local_bar_white_24dp,
R.drawable.ic_directions_car_white_24dp
};
*/
public SimpleFragmentPagerAdapter(FragmentManager fm) {
super(fm);
this.context = context;
}
@Override
public int getCount() {
return PAGE_COUNT;
}
@Override
public Fragment getItem(int position) {
if (position == 0) {
return new NumbersFragment();
} else if (position == 1){
return new FamilyFragment();
} else if (position == 2){
return new ColorsFragment();
} else {
return new PhrasesFragment();
}
}
@Override
// Generate title based on item position
public CharSequence getPageTitle(int position) {
//If you work with text in the tabs
return tabTitles[position];
//If you work with icons in the tabs
/*
Drawable image = context.getResources().getDrawable(imageResId[position]);
image.setBounds(0, 0, image.getIntrinsicWidth(), image.getIntrinsicHeight());
SpannableString sb = new SpannableString(" ");
ImageSpan imageSpan = new ImageSpan(image, ImageSpan.ALIGN_BOTTOM);
sb.setSpan(imageSpan, 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
return sb;
*/
}
}
MainActivity：
package com.example.android.miwok;
import android.content.Context;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.content.Intent;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
/**
* Displays a {@link ViewPager} where each page shows a different page.
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set the content of the activity to use the activity_main.xml layout file
setContentView(R.layout.activity_main);
// Find the view pager that will allow the user to swipe between fragments
ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
// Create an adapter that knows which fragment should be shown on each page
SimpleFragmentPagerAdapter adapter = new SimpleFragmentPagerAdapter(getSupportFragmentManager());
// Set the adapter onto the view pager
if (viewPager != null) {
viewPager.setAdapter(adapter);
}
// Give the Tab layout the ViewPager
TabLayout tabLayout = (TabLayout) findViewById(R.id.sliding_tabs);
if (tabLayout != null) {
tabLayout.setupWithViewPager(viewPager);
}
}
}
logcat的：
03-21 13:53:00.450 1971-1971/? I/art: Late-enabling -Xcheck:jni
03-21 13:53:00.470 1971-1978/? E/art: Failed sending reply to debugger: Broken pipe
03-21 13:53:00.470 1971-1978/? I/art: Debugger is no longer active
03-21 13:53:00.470 1971-1978/? I/art: Starting a blocking GC Instrumentation
03-21 13:53:00.582 1971-1971/? W/System: ClassLoader referenced unknown path: /data/app/com.example.android.miwok-1/lib/arm64
03-21 13:53:00.591 1971-1971/? I/InstantRun: Starting Instant Run Server for com.example.android.miwok
03-21 13:53:01.128 1971-1971/? 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
03-21 13:53:01.222 1971-1971/? D/AndroidRuntime: Shutting down VM
03-21 13:53:01.223 1971-1971/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.miwok, PID: 1971
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.miwok/com.example.android.miwok.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2711)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2772)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:241)
at android.app.ActivityThread.main(ActivityThread.java:6217)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at com.example.android.miwok.SimpleFragmentPagerAdapter.getPageTitle(SimpleFragmentPagerAdapter.java:69)
at android.support.design.widget.TabLayout.populateFromPagerAdapter(TabLayout.java:773)
at android.support.design.widget.TabLayout.setPagerAdapter(TabLayout.java:764)
at android.support.design.widget.TabLayout.setupWithViewPager(TabLayout.java:716)
at com.example.android.miwok.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:6705)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2664)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2772)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:241)
at android.app.ActivityThread.main(ActivityThread.java:6217)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)