Question

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

public class MainActivity extends FragmentActivity {

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

        ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
        pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
    }

    private class MyPagerAdapter extends FragmentPagerAdapter {

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int pos) {
            switch(pos) {

            case 0: return FirstFragment.newInstance("FirstFragment, Instance 1");
            case 1: return SecondFragment.newInstance("SecondFragment, Instance 1");
            case 2: return ThirdFragment.newInstance("ThirdFragment, Instance 1");
            case 3: return ThirdFragment.newInstance("ThirdFragment, Instance 2");
            case 4: return ThirdFragment.newInstance("ThirdFragment, Instance 3");
            default: return ThirdFragment.newInstance("ThirdFragment, Default");
            }
        }

        @Override
        public int getCount() {
            return 5;
        }       
    }
}

我收到类型不匹配错误。基本上它说它无法将活动转换为片段。根据我的阅读，它与我的进口有关。任何人都可以帮助我吗？

Answer 1

我知道它已经很晚了，但我提交了这个答案，因为它发生在许多开发者身上。

由于库导入冲突而出现此错误。检查FirstFragment，SecondFragment和ThirdFragment中的导入，确保您使用的是相同的片段库。

如果您使用旧版API的片段，则需要导入android.support.v4.app.Fragment;

但是如果您使用Fragments来使用更新的API android.app.Fragment;

当您使用自动完成来完成类名时，您可能不会注意到要导入的库。

Answer 2

请查看下面的代码。我向您展示并向您展示如何创建寻呼机视图：

MainActivity类：

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

public class MainActivity extends FragmentActivity {

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

        ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
        pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
    }
}

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
                android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
                android:paddingRight="@dimen/activity_horizontal_margin"
                android:paddingTop="@dimen/activity_vertical_margin"
                android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <!-- it is important to use ViewPager from support library -->
    <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

</RelativeLayout>

MyPagerAdapter.class

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;

public  class MyPagerAdapter extends FragmentStatePagerAdapter {

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int pos) {
        switch (pos) {

            case 0:
                return FirstFragment.newInstance("FirstFragment, Instance 1");
            case 1:
                return SecondFragment.newInstance("SecondFragment, Instance 1");
            case 2:
                return ThirdFragment.newInstance("ThirdFragment, Instance 1");
            case 3:
                return ThirdFragment.newInstance("ThirdFragment, Instance 2");
            case 4:
                return ThirdFragment.newInstance("ThirdFragment, Instance 3");
            default:
                return ThirdFragment.newInstance("ThirdFragment, Default");
        }
    }

    @Override
    public int getCount() {
        return 5;
    }
}

fragment_layout.xml 我为所有片段创建了通用布局。我将更改背景颜色并在下面的源代码中设置文本。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:orientation="vertical"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
    <TextView
            android:id="@+id/text_view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"/>
</RelativeLayout>

FirstFragment.class

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class FirstFragment extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v =inflater.inflate(R.layout.fragment_layout, container, false);
        v.setBackgroundColor(Color.RED);
        TextView textView = (TextView) v.findViewById(R.id.text_view);
        textView.setText(getArguments().getString("value"));
        return v;
    }

    public static FirstFragment newInstance(String s) {
        Bundle args = new Bundle();
        args.putString("value", s);
        FirstFragment result = new FirstFragment();
        result.setArguments(args);
        return result;
    }
}

SecondFragment.class

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class SecondFragment extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View v =inflater.inflate(R.layout.fragment_layout, container, false);
        v.setBackgroundColor(Color.GRAY);
        TextView textView = (TextView) v.findViewById(R.id.text_view);
        textView.setText(getArguments().getString("value"));
        return v;
    }

    public static SecondFragment newInstance(String s) {
        Bundle args = new Bundle();
        args.putString("value", s);
        SecondFragment result = new SecondFragment();
        result.setArguments(args);
        return result;
    }
}

ThirdFragment.class

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class ThirdFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_layout, container, false);
        v.setBackgroundColor(Color.BLUE);
        TextView textView = (TextView) v.findViewById(R.id.text_view);
        textView.setText(getArguments().getString("value"));
        return v;
    }

    public static ThirdFragment newInstance(String s) {
        Bundle args = new Bundle();
        args.putString("value", s);
        ThirdFragment result = new ThirdFragment();
        result.setArguments(args);
        return result;
    }
}

这是完整的程序，显示带有文本的5个片段，作为参数传递。请试一试。如果您的解决方案中还有一个问题或其他问题尚不清楚，或者我的解决方案对您没有帮助。来吧，请问。：）

类型不匹配无法从My Activity转换为Fragment

2 个答案: