我正试图让这个图表包起作用：
https://github.com/PhilJay/MPAndroidChart/wiki/Getting-Started
我遇到的问题不在于软件包，但我对如何定义XML以及如何从代码中引用XML缺乏了解。
这是我的班级绘制LineGraph：
import com.github.mikephil.charting.charts.LineChart;
import com.github.mikephil.charting.data.Entry;
import com.github.mikephil.charting.data.LineData;
import com.github.mikephil.charting.data.LineDataSet;
import android.support.v7.app.AppCompatActivity;
import java.util.ArrayList;
import java.util.List;
public class ChartHandler extends AppCompatActivity {
public void initLineChart() {
// in this example, a LineChart is initialized from xml
LineChart chart = (LineChart) findViewById(R.id.chart);
ArrayList<Integer> data = new ArrayList<Integer>();
data.add(10);
data.add(20);
data.add(30);
data.add(40);
data.add(50);
List<Entry> entries = new ArrayList<Entry>();
for (Integer item : data) {
// turn your data into Entry objects
entries.add(new Entry(item, item));
}
LineDataSet dataSet = new LineDataSet(entries, "Label"); // add entries to dataset
dataSet.setColor(170);
dataSet.setValueTextColor(0);
LineData lineData = new LineData(dataSet);
chart.setData(lineData);
chart.invalidate(); // refresh
}
}
我不清楚在哪里为图表定义XML，我已将其作为值/ linechart.xml下的新文件添加：
<?xml version="1.0" encoding="utf-8"?>
当我构建时，我得到一个错误，Charthandler.java无法找到符号图表。
注意：如果我在现有的content_main.xml布局中添加此XML，然后将我的代码复制到MainActivity的onCreate函数中，那么它可以工作，但我希望能够在单独的类和XML定义中组织代码在他们自己的文件中
更新
我创建了一个新文件res / layout / linechart.xml
<?xml version="1.0" encoding="utf-8"?>
<com.github.mikephil.charting.charts.LineChart xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/chart"
android:layout_width="368dp"
android:layout_height="495dp"
tools:layout_editor_absoluteY="8dp"
tools:layout_editor_absoluteX="8dp">
</com.github.mikephil.charting.charts.LineChart>
构建完成，但是当我的代码试图找到id：
时，我收到运行时错误07-20 11:38:10.361 1290-1290/com.testapp.cloudsnifferclient E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.testapp.cloudsnifferclient, PID: 1290
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.testapp.cloudsnifferclient/com.testapp.cloudsnifferclient.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.LineChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)
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:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.github.mikephil.charting.charts.LineChart.setData(com.github.mikephil.charting.data.ChartData)' on a null object reference
at com.testapp.MainActivity.onCreate(MainActivity.java:71)
at android.app.Activity.performCreate(Activity.java:6288)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)
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:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
答案 0 :(得分：1)
将其置于res / layout下以解决您的问题