我只是在尝试该库，以查看它是否符合我的需求，到目前为止，我还无法使它正常工作。这是代码
package com.example.user.bottomnavigationbar;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;
import com.github.mikephil.charting.charts.PieChart;
import com.github.mikephil.charting.data.PieData;
import com.github.mikephil.charting.data.PieDataSet;
import com.github.mikephil.charting.data.PieEntry;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
PieChart pc;
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
= new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.navigation_home:
return true;
// case R.id.navigation_overview:
// Intent intentOverview = new Intent(MainActivity.this, activity_test.class);
// intentOverview.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
// MainActivity.this.finish();
// startActivity(intentOverview);
// return true;
case R.id.navigation_expenses:
return true;
case R.id.navigation_reminder:
return true;
case R.id.navigation_income:
return true;
case R.id.navigation_login:
Intent intentLogin = new Intent(MainActivity.this, LoginActivity.class);
intentLogin.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
MainActivity.this.finish();
startActivity(intentLogin);
return true;
}
return false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState)
{
pc = findViewById(R.id.chart);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navigation = findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
ArrayList <PieEntry> pieData = new ArrayList<>();
pieData.add(new PieEntry(10));
pieData.add(new PieEntry(20));
pieData.add(new PieEntry(30));
PieDataSet dataSet = new PieDataSet(pieData, "Survey Results");
PieData data = new PieData(dataSet);
pc.setData(data);
}
public void onBackPressed()
{
new AlertDialog.Builder(this)
.setIcon(android.R.drawable.ic_dialog_alert)
.setTitle("Closing Activity")
.setMessage("Are you sure you want to close this activity?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener()
{
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
这是我得到的错误
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.user.bottomnavigationbar, PID: 4172
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.bottomnavigationbar/com.example.user.bottomnavigationbar.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.PieChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
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.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.PieChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
at com.example.user.bottomnavigationbar.MainActivity.onCreate(MainActivity.java:78)
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)
我搜索了一下，发现对别人来说，他们没有初始化对象，因此它引发了此错误。现在有人确实提到可以用代码创建图表，然后将其添加到活动中，如文档的“入门”页面所建议的那样，但我无法使其正常工作。那有什么呢？
P.S留在代码中进行导航，因为我不确定是否可能是问题的原因
答案 0 :(得分：0)
您首先要找到该视图，然后将内容视图提供给您的活动，并替换为此代码
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pc = findViewById(R.id.chart);
BottomNavigationView navigation = findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
ArrayList <PieEntry> pieData = new ArrayList<>();
pieData.add(new PieEntry(10));
pieData.add(new PieEntry(20));
pieData.add(new PieEntry(30));
PieDataSet dataSet = new PieDataSet(pieData, "Survey Results");
PieData data = new PieData(dataSet);
pc.setData(data);
}