Question

我有两个java文件。一个MainActivity文件和一个apclass文件。我想制作一个数学Android应用程序，它可以找到许多AP的术语，ap和其他的总和。

但问题是它给错误（红线）

我的主要活动

package com.pradeep.apgphp;

import android.support.design.widget.TabLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;    

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);
    tabLayout.setupWithViewPager(mViewPager);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
            return;
        }
    });

}    


@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);
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int position) {
      switch (position){
          case 0:
              apclass tab1 = new apclass();
              return tab1;
          case 1:
              gpclass tab2 = new gpclass();
              return tab2;
          case 2:
              hpclass tab3 = new hpclass();
              return tab3;
              default:
                  return null;
      }

    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return "AP";
            case 1:
                return "GP";
            case 2:
                return "HP";
        }
        return null;
    }
}

}

和我的AP CLASSA

package com.pradeep.apgphp;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
public class apclass  extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.activity_ap, container, true);
    return rootView;
}

}

现在，当我尝试添加按钮并希望发送一些值时，它会在其下面显示一条红线

按钮A =（按钮）findViewById（R.id.a）;

如果我添加此类型，那么我将面临错误。

Answer 1

如果您的按钮在班级a中，则需要编写以下代码：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                     Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_ap, container, true);
Button A = (Button) rootview.findViewById(R.id.a);
return rootView;}

希望有所帮助:)

Answer 2

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.activity_ap, container, false);
    Button A = (Button) rootView.findViewById(R.id.a);
    return rootView;
}

试试这个。

Answer 3

你向你的apclass夸大了一个布局..现在你无法从它直接访问元素id。当你使用

setContentView(R.layout.layoutname);

尝试

Button b1=(Button)findViewById(R.id.id);

当您为布局充气时，我们只能从视图中访问布局元素。所以请使用如下

 Button b1=(Button)rootView.findViewById(R.id.id);

希望它能帮到你

无法添加任何Button操作

3 个答案: