当ViewPager设置FragmentPagerAdapter

Question

我有两个活动，父母和孩子。使用Intent发生2之间的数据传递。我根据微调器的值设置一个或两个选项卡。标签和TableLayout显示在第二页上。

问题是：当我设置FragmentStatePageAdapter时，onCreateView中的TabFragment1没有被调用，程序因错误而崩溃

Abhishek

错误：

  

原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“ void android.widget.TableLayout.addView（android.view.View，android.view.ViewGroup $ LayoutParams）”
      在finance.banking.comparefd.CalFDActivity.addHeaders（CalFDActivity.java:292）
      在finance.banking.comparefd.CalFDActivity.onCreate（CalFDActivity.java:205）
      在android.app.Activity.performCreate（Activity.java:6237）

代码：

package finance.banking.comparefd;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v7.app.AppCompatActivity;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Spinner;
import android.widget.TableLayout;
import android.widget.Toast;

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

//import android.support.v4.view.PagerAdapter;



public class MainActivity extends AppCompatActivity implements 
  AdapterView.OnItemSelectedListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

         TabLayout tabLayout =  findViewById(R.id.tab_layout);
         tabLayout.addTab(tabLayout.newTab().setText("Testing"));

        final EditText amtDeposited = findViewById(R.id.amtDeposit);



        Button button=findViewById(R.id.btnCalc);

        // Spinner element
        final Spinner spinner =  findViewById(R.id.spinner);


        // Spinner click listener
        spinner.setOnItemSelectedListener(this);

        // Spinner Drop down elements
        List<String> categories = new ArrayList<>();
        categories.add("--Select--");
        categories.add("1");
        categories.add("2");
        categories.add("3");
        categories.add("3-5");


        // Creating adapter for spinner
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<>(this, 
     android.R.layout.simple_spinner_item, categories);

        // Drop down layout style - list view with radio button

     dataAdapter.
        setDropDownViewResource(
                 android.R.layout.simple_spinner_dropdown_item 
            );

        // attaching data adapter to spinner
        spinner.setAdapter(dataAdapter);


        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Toast.makeText(getBaseContext(), result.toString(),
                        Toast.LENGTH_LONG).show();

                final RadioGroup radioGroup = findViewById(R.id.radio_group);

                Toast.makeText(getBaseContext(), 
       String.valueOf(radioGroup.getCheckedRadioButtonId()), 
    Toast.LENGTH_LONG).show();

                Toast.makeText(getBaseContext(), ((RadioButton) 
    findViewById(radioGroup.getCheckedRadioButtonId()))
                                .getText().toString(), 
     Toast.LENGTH_LONG).show();

                Intent intent = new Intent(getBaseContext(), 
    CalFDActivity.class);
                startActivity(intent);

            }
        });
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int 
   position, long id) {
        // On selecting a spinner item
        TableLayout tl =  findViewById(R.id.table1);
        TabLayout tabLayout3 =  findViewById(R.id.tab_layout);
        TableLayout tlH =  findViewById(R.id.headerTable);

        if (tl!=null ) {
            tabLayout3.removeAllTabs();
            tabLayout3.addTab(tabLayout3.newTab().setText("Testing"));
            tl.removeAllViews();
            tlH.removeAllViews();
        }

        // Showing selected spinner item
       // Toast.makeText(parent.getContext(), "Selected: " + item, 
    Toast.LENGTH_LONG).show();

    }


    @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 void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub

    }
}

---

package finance.banking.comparefd;

import android.content.Intent;
import android.graphics.Color;
import android.graphics.Typeface;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.Gravity;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;

   import java.text.NumberFormat;
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Locale;
    import java.util.Map;

    public class CalFDActivity extends AppCompatActivity  {


    List<> tabData = new ArrayList<>();
    ViewPager v;

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

        Intent intent = getIntent();

        TabLayout tabLayout = findViewById(R.id.tab_layout1);

        v = selectTabFragment(tabLayout);

        showData(v, tabLayout);

        Log.d("Android Fragment ", "" + v);

        TableLayout tlH = v.findViewById(R.id.headerTable);
        TableLayout tl =  v.findViewById(R.id.table1);

        //tl.removeAllViews();
        addHeaders(tlH);
        addData(tl, tabData);

    }

    private void showData(final ViewPager v, TabLayout tabLayout) {
        v.addOnPageChangeListener(new 
 TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new 
 TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                if (tab.getPosition() == 1) {
                    tabData = new ArrayList<>();
                    TableLayout tlH =  findViewById(R.id.headerTable1);
                    TableLayout tl = findViewById(R.id.table2);
                    tlH.removeAllViews();
                    tl.removeAllViews();
                    addHeaders(tlH);
                    addData(tl, tabData);
                }
                v.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });
    }



    public void addData(TableLayout tl, List<FDData> tabData) {

        for (int i = 0; i < tabData.size(); i++) {
            TableRow tr = new TableRow(this);
            tr.setLayoutParams(getLayoutParams());
            tr.addView(getTextView(i + 1, tabData.get(i).getName(), 
 Color.BLACK, Typeface.NORMAL, Color.WHITE, 20, 30));
            tr.addView(getTextView(i + 2, tabData.get(i).getCity(), 
 Color.BLACK, Typeface.NORMAL, Color.WHITE, 30, 30));
            tr.addView(getTextView(i + 3, tabData.get(i).getAddress, 
 Color.BLACK, Typeface.NORMAL, Color.WHITE, 20, 30));
            tr.addView(getTextView(i + 4, tabData.get(i).getHobby, 
 Color.BLACK, Typeface.NORMAL, Color.WHITE, 20, 30));
            tl.addView(tr, getLayoutParams());
        }
    }

    public void addHeaders(TableLayout tl) {

        TableRow tr = new TableRow(this);
        Log.d("Android: ", "Before 1");
        tr.setLayoutParams(getLayoutParams());
        Log.d("Android: ", "After 1");
        tr.addView(getTextView(1, "Name", Color.WHITE, Typeface.BOLD, 
  Color.BLUE, 20, 80));
        Log.d("Android: ", "After 2");
        tr.addView(getTextView(2, "City", Color.WHITE, Typeface.BOLD, 
  Color.BLUE, 30, 80));
        tr.addView(getTextView(3, "Address", Color.WHITE, Typeface.BOLD, 
  Color.BLUE, 20, 80));
        tr.addView(getTextView(4, "Hobby", Color.WHITE, Typeface.BOLD, 
  Color.BLUE, 20, 80));
        Log.d("Android: ", "After 3");
        tl.addView(tr, getTblLayoutParams());
        Log.d("Android: ", "After 4");
    }

    private TableRow.LayoutParams getLayoutParams() {
     /*        LayoutParams params = new LayoutParams(
                LayoutParams.WRAP_CONTENT,
                LayoutParams.WRAP_CONTENT);*/
        TableRow.LayoutParams params = new TableRow.LayoutParams(
                TableRow.LayoutParams.WRAP_CONTENT,
                TableRow.LayoutParams.WRAP_CONTENT);
        params.setMargins(2, 2, 2, 2);
        return params;
    }

    private TextView getTextView(int id, String title, int color, int 
   typeface, int bgColor, int widthInPercentOfScreenWidth, int 
    fixedHeightInPixels) {
        TextView tv = new TextView(this);
        tv.setId(id);
        tv.setText(title);
        tv.setTextColor(color);
        tv.setGravity(Gravity.CENTER);
        //tv.setPadding(0, 10, 10, 0);
        tv.setTypeface(Typeface.DEFAULT, typeface);
        tv.setBackgroundColor(bgColor);
        tv.setLayoutParams(getLayoutParams());
        tv.setWidth(100);
        tv.setHeight(fixedHeightInPixels);
        //tv.setOnClickListener(this);
        return tv;
    }

    private TableLayout.LayoutParams getTblLayoutParams() {
        Log.d("Android: ", "Inside getTblLayoutParams");
        return new TableLayout.LayoutParams(
                TableRow.LayoutParams.WRAP_CONTENT,
                TableRow.LayoutParams.WRAP_CONTENT);
    }



    public ViewPager selectTabFragment(TabLayout tabLayout) {
        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

        v = findViewById(R.id.pager);
        CustomPagerAdapter adapter = new 
  CustomPagerAdapter(getSupportFragmentManager(), 
   tabLayout.getTabCount(),getBaseContext());
        v.setAdapter(adapter);
        return v;
    }
}

---

package finance.banking.comparefd;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class TabFragment1 extends Fragment {


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup 
    container, Bundle savedInstanceState) {
        Log.d("Android: ", "Inside TabFragment1");
        return inflater.inflate(R.layout.tab_fragment_1, container, false);
    }
  }

---

package finance.banking.comparefd;

import android.content.Context;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.util.Log;

public class CustomPagerAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;
    Context context;

    public CustomPagerAdapter(FragmentManager fm, int NumOfTabs, Context 
  context) {
        super(fm);
        Log.d("Android: ", "Inside Constructor");
        this.mNumOfTabs = NumOfTabs;
        this.context = context;
    }

    @Override
    public Fragment getItem(int position) {
        Log.d("Android: ","Inside PagerAdapter");
        Log.d("Position: ",String.valueOf(position));

        switch (position) {
            case 0:
                //TabFragment1 tab1 = (TabFragment1) 
  Fragment.instantiate(context, TabFragment1.class.getName());
                return new TabFragment1();
            case 1:
                //TabFragment2 tab2 = (TabFragment2) 
  Fragment.instantiate(context, TabFragment2.class.getName());
                return new TabFragment2();
            case 2:
                //TabFragment3 tab3 = (TabFragment3) 
  Fragment.instantiate(context, TabFragment3.class.getName());
                return new TabFragment3();
            default:
                return null;
        }
    }

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