java - 奇怪的错误。 "return mFragmentList.get(position);"行不兼容类型错误

Question

我是新手。我正在关注 http://www.androidhive.info/2015/09/android-material-design-working-with-tabs/ 上的滑动标签 Activity 教程。

我在“return mFragmentList.get(position);”处收到奇怪的错误提示 Incompatible Types在 MainActivity.java 请帮助。

主 Activity .java

    package com.pixalstudio.musicadda;

import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toolbar;
import android.support.v4.app.Fragment;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
    }

    private void setSupportActionBar(Toolbar toolbar) {
    }

    private void setupViewPager(ViewPager viewPager) {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new OneFragment(), "ONE");
        adapter.addFragment(new TwoFragment(), "TWO");
        adapter.addFragment(new ThreeFragment(), "THREE");
        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<android.app.Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public android.support.v4.app.Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(android.app.Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }
}

如果有人需要其他帮助，请告诉我。提前谢谢 :)

洛格卡特

    03-04 21:38:22.643 2650-2650/com.pixalstudio.musicadda E/AndroidRuntime: FATAL EXCEPTION: main
                                                                         Process: com.pixalstudio.musicadda, PID: 2650
                                                                         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pixalstudio.musicadda/com.pixalstudio.musicadda.MainActivity}: java.lang.ClassCastException: android.support.v7.widget.Toolbar cannot be cast to android.widget.Toolbar
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                             at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:135)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at java.lang.reflect.Method.invoke(Method.java:372)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                          Caused by: java.lang.ClassCastException: android.support.v7.widget.Toolbar cannot be cast to android.widget.Toolbar
                                                                             at com.pixalstudio.musicadda.MainActivity.onCreate(MainActivity.java:26)
                                                                             at android.app.Activity.performCreate(Activity.java:5990)
                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                             at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                             at android.os.Looper.loop(Looper.java:135) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                             at java.lang.reflect.Method.invoke(Native Method) 
                                                                             at java.lang.reflect.Method.invoke(Method.java:372) 
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
03-04 21:38:22.645 1519-1887/system_process W/ActivityManager:   Force finishing activity 1 com.pixalstudio.musicadda/.MainA

Activity

构建.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"

    defaultConfig {
        applicationId "com.pixalstudio.musicadda"
        minSdkVersion 14
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.2.0'
    compile 'com.android.support:design:23.2.0'
    compile 'com.android.support:support-v4:23.2.0'
}

Answer 1

改变:

private final List<android.app.Fragment> mFragmentList = new ArrayList<>();

收件人:

private final List<Fragment> mFragmentList = new ArrayList<>();

您没有像在其他任何地方那样使用支持 fragment 。

与 addFragment 方法相同:

public void addFragment(Fragment fragment, String title) {
    mFragmentList.add(fragment);
    mFragmentTitleList.add(title);
}

您可以只用 Fragment 替换这些行，因为您正在导入支持库 fragment import android.support.v4.app.Fragment;。

另请注意，OneFragment、TwoFragment 和 ThreeFragment 必须从支持库 fragment 扩展，如果它们尚未扩展的话。

根据发布的新日志，您还需要从支持库中导入工具栏。

import android.support.v7.widget.Toolbar;