MPAndroidChart 未显示在片段中

Question

我在 android studio 中使用 MPAndroidChart 库来制作图表。图表在活动中显示良好，但我无法在片段中使用它们。尝试使用不同的图表，但我无法解决问题。即使我正在向图表提供数据，我也会收到一条消息“没有可用的图表数据”。所以基本上我有一个名为 ExamPerformanceActivity 的活动（带有底部导航栏），它有三个片段 MathsFragment、PhysicsFragment、ChemistryFragment。我在面临问题的 MathsFragment 中有一个条形图。

activity_exam_performance.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
android:id="@+id/activity_main"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.peepstake.vijay.statlog.ExamPerfoActivity">

<FrameLayout
    android:id="@+id/frame_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_above="@+id/navigation"
    android:animateLayoutChanges="true">
</FrameLayout>

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:background="@color/colorPrimary"
    app:itemIconTint="#d5d6d9"
    app:itemTextColor="#ffffff"
    app:menu="@menu/bottombar_student_items"/>
  </RelativeLayout>

ExamPerformanceActivity.java

public class ExamPerformanceActivity extends AppCompatActivity {



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

    BottomNavigationView bottomNavigationView = (BottomNavigationView)
            findViewById(R.id.navigation);

    bottomNavigationView.setOnNavigationItemSelectedListener
            (new BottomNavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                    Fragment selectedFragment = null;
                    switch (item.getItemId()) {
                        case R.id.maths:
                            selectedFragment = MathsFragment.newInstance();
                            break;
                        case R.id.physics:
                            selectedFragment = PhysicsFragment.newInstance();
                            break;
                        case R.id.chemistry:
                            selectedFragment = ChemistryFragment.newInstance();
                            break;
                    }
                    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                    transaction.replace(R.id.frame_layout, selectedFragment);
                    transaction.commit();
                    return true;
                }
            });

    //Manually displaying the first fragment - one time only
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.frame_layout, MathsFragment.newInstance());
    transaction.commit();

    //Used to select an item programmatically
    //bottomNavigationView.getMenu().getItem(2).setChecked(true);

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        // Respond to the action bar's Up/Home button
        case android.R.id.home:
            NavUtils.navigateUpFromSameTask(this);
            return true;
    }
    return super.onOptionsItemSelected(item);
}
public void goTopicwise(View v){
    Intent intent = new Intent(ExamPerformanceActivity.this, TopicwiseActivity.class);
    startActivity(intent);
}

}

fragment_maths.xml

<FrameLayout 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"
tools:context="com.peepstake.vijay.statlog.Common.MathsFragment">


<com.github.mikephil.charting.charts.BarChart
    android:id="@+id/bar"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</com.github.mikephil.charting.charts.BarChart>

</FrameLayout>

MathsFragment.java

public class MathsFragment extends Fragment {
BarChart bar;

public static MathsFragment newInstance() {
    MathsFragment fragment = new MathsFragment();
    return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

public MathsFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    View view =inflater.inflate(R.layout.fragment_maths, container, false);

    Typeface font = Typeface.createFromAsset(getActivity().getAssets(), "fonts/ProductSans.ttf");

    bar = (BarChart)view.findViewById(R.id.bar);

    List<BarEntry> entries = new ArrayList<>();
    entries.add(new BarEntry(0f, 100f,"Total"));
    entries.add(new BarEntry(1f, 82f,"Obtained"));
    entries.add(new BarEntry(2f, 95f,"Highest"));
    entries.add(new BarEntry(3f, 69f,"Average"));



    BarDataSet bSet = new BarDataSet(entries, "Marks");
    bSet.setColors(ColorTemplate.VORDIPLOM_COLORS);

    ArrayList<String> barFactors = new ArrayList<>();
    barFactors.add("Total");
    barFactors.add("Obtained");
    barFactors.add("Highest");
    barFactors.add("Average");


    XAxis xAxis = bar.getXAxis();
    xAxis.setGranularity(1f);
    xAxis.setGranularityEnabled(true);
    BarData data = new BarData(bSet);
    data.setBarWidth(0.9f); // set custom bar width
    data.setValueTextSize(12);
    Description description = new Description();
    description.setTextColor(R.color.colorPrimary);
    description.setText("All values in marks");
    bar.setDescription(description);
    bar.setData(data);
    bar.setFitBars(true); // make the x-axis fit exactly all bars
    bar.invalidate(); // refresh
    bar.getXAxis().setValueFormatter(new IndexAxisValueFormatter(barFactors));

    Legend l = bar.getLegend();
    l.setFormSize(10f); // set the size of the legend forms/shapes
    l.setForm(Legend.LegendForm.CIRCLE); // set what type of form/shape should be used
    l.setTypeface(font);
    l.setTextSize(12f);
    l.setTextColor(Color.BLACK);
    List<LegendEntry> lentries = new ArrayList<>();
    for (int i = 0; i < barFactors.size(); i++) {
        LegendEntry entry = new LegendEntry();
        entry.formColor = ColorTemplate.VORDIPLOM_COLORS[i];
        entry.label = barFactors.get(i);
        lentries.add(entry);
    }
    l.setXEntrySpace(5f); // set the space between the legend entries on the x-axis
    l.setYEntrySpace(5f);
    l.setCustom(lentries);

    return inflater.inflate(R.layout.fragment_maths, container, false);
}

}

My Output screen

Answer 1

将onCreateView 方法的最后一行更改为以下内容：

l.setCustom(lentries);
//return inflater.inflate(R.layout.fragment_maths, container, false);
return view;

图表现在将正确显示：

为什么？该方法的第一行：

View view = inflater.inflate(R.layout.fragment_maths, container, false);

膨胀一个 View 对象，它是该片段的 contentView。

然后你调用：

bar = (BarChart)view.findViewById(R.id.bar);

在同一个 View 对象上获取BarChart 的句柄，然后将数据添加到其中。

但是，在方法末尾的原始代码中，您膨胀了一个新的 contentView，从而丢弃了您添加数据的 View 和 BarChart。换句话说，原始方法设置图表然后丢弃它，将其替换为空的BarChart，这是膨胀视图的简单结果。