我试图从json文件中获取数据，以便稍后可以使用aChartEngine。这是我用来获取这些数据的方法：
public String loadJSONFromAsset() {
String json = null;
try {
InputStream is = this.getAssets().open(ficheiro);
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
return json;
}
我在其他类中使用此方法，我只在列表视图中显示json数据（即使没有在getAssets（）之前提供上下文），但是我无法将其转换为这次工作。
logcat的：
05-20 10:26:14.108: E/AndroidRuntime(6388): FATAL EXCEPTION: main
05-20 10:26:14.108: E/AndroidRuntime(6388): Process: com.example.euroxxi_testeficheiro, PID: 6388
05-20 10:26:14.108: E/AndroidRuntime(6388): java.lang.IllegalStateException: Could not execute method of the activity
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.view.View$1.onClick(View.java:3969)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.view.View.performClick(View.java:4633)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.view.View$PerformClick.run(View.java:19330)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.os.Handler.handleCallback(Handler.java:733)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.os.Handler.dispatchMessage(Handler.java:95)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.os.Looper.loop(Looper.java:157)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.app.ActivityThread.main(ActivityThread.java:5356)
05-20 10:26:14.108: E/AndroidRuntime(6388): at java.lang.reflect.Method.invokeNative(Native Method)
05-20 10:26:14.108: E/AndroidRuntime(6388): at java.lang.reflect.Method.invoke(Method.java:515)
05-20 10:26:14.108: E/AndroidRuntime(6388): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
05-20 10:26:14.108: E/AndroidRuntime(6388): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
05-20 10:26:14.108: E/AndroidRuntime(6388): at dalvik.system.NativeStart.main(Native Method)
05-20 10:26:14.108: E/AndroidRuntime(6388): Caused by: java.lang.reflect.InvocationTargetException
05-20 10:26:14.108: E/AndroidRuntime(6388): at java.lang.reflect.Method.invokeNative(Native Method)
05-20 10:26:14.108: E/AndroidRuntime(6388): at java.lang.reflect.Method.invoke(Method.java:515)
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.view.View$1.onClick(View.java:3964)
05-20 10:26:14.108: E/AndroidRuntime(6388): ... 11 more
05-20 10:26:14.108: E/AndroidRuntime(6388): Caused by: java.lang.NullPointerException
05-20 10:26:14.108: E/AndroidRuntime(6388): at android.content.ContextWrapper.getAssets(ContextWrapper.java:88)
05-20 10:26:14.108: E/AndroidRuntime(6388): at com.example.euroxxi_testeficheiro.ChartTeste.loadJSONFromAsset(ChartTeste.java:53)
05-20 10:26:14.108: E/AndroidRuntime(6388): at com.example.euroxxi_testeficheiro.ChartTeste.getIntent(ChartTeste.java:91)
05-20 10:26:14.108: E/AndroidRuntime(6388): at com.example.euroxxi_testeficheiro.MainActivity.ChartPlot(MainActivity.java:77)
05-20 10:26:14.108: E/AndroidRuntime(6388): ... 14 more
这是完整的活动
package com.example.euroxxi_testeficheiro;
import java.io.IOException;
import java.io.InputStream;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import org.achartengine.ChartFactory;
import org.achartengine.chart.BarChart.Type;
import org.achartengine.model.CategorySeries;
import org.achartengine.model.XYMultipleSeriesDataset;
import org.achartengine.renderer.XYMultipleSeriesRenderer;
import org.achartengine.renderer.XYSeriesRenderer;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.jjoe64.graphview.BarGraphView;
import com.jjoe64.graphview.GraphViewSeries;
import com.jjoe64.graphview.GraphView.GraphViewData;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ListView;
public class ChartTeste extends Activity{
private static final String TAG_CENTRAL = "getCentrais_JSONResult";
private static final String TAG_NOME = "Central";
private static final String TAG_DATA = "Data";
private static final String TAG_PRODUCAO = "Producao";
String ficheiro = "getCentrais_JSON.json";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chart_teste);
getIntent();
}
public String loadJSONFromAsset() {
String json = null;
try {
InputStream is = getApplicationContext().getAssets().open("getCentrais_JSON.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
return json;
}
public Intent getIntent(Context context)
{
XYMultipleSeriesDataset dataset = new XYMultipleSeriesDataset();
XYMultipleSeriesRenderer mRenderer = new XYMultipleSeriesRenderer();
try {
String nome;
int producao;
// contacts JSONArray
JSONArray centrais = null;
JSONObject jsonObj = new JSONObject(loadJSONFromAsset());
// Getting JSON Array node
centrais = jsonObj.getJSONArray(TAG_CENTRAL);
int[] y={0};
String[] xLabel = {""};
// looping through All Contacts
for (int i = 0; i < centrais.length(); i++) {
JSONObject c = centrais.getJSONObject(i);
//String id = c.getString(TAG_ID);
nome = c.getString(TAG_NOME);
producao = c.getInt(TAG_PRODUCAO);
xLabel[i]=nome;
y[i]=producao;
mRenderer.addXTextLabel(y[i], xLabel[i]);
}
// Bar 1
CategorySeries series = new CategorySeries("Grafico de producao");
for (int j = 0; j < y.length; j++) {
series.add("Bar " + (j+1), y[j]);
}
dataset.addSeries(series.toXYSeries());
// This is how the "Graph" itself will look like
mRenderer.setChartTitle("Gráfico de produção");
mRenderer.setXTitle("X VALUES");
mRenderer.setYTitle("Y VALUES");
mRenderer.setXLabels(0);
mRenderer.setAxesColor(Color.GREEN);
mRenderer.setLabelsColor(Color.RED);
// Customize bar 1
XYSeriesRenderer renderer = new XYSeriesRenderer();
renderer.setDisplayChartValues(true);
renderer.setChartValuesSpacing((float) 0.5);
mRenderer.addSeriesRenderer(renderer);
//renderer.setChartTitleTextSize(titleSize); // if we change title text size, it will render off screen
mRenderer.setLabelsTextSize(25);
mRenderer.setLegendTextSize(25);
} catch (JSONException e) {
e.printStackTrace();
}
Intent intent = ChartFactory.getBarChartIntent(context, dataset,mRenderer, Type.DEFAULT);
return intent;
}
}
答案 0 :(得分：2)
堆栈跟踪表明ChartTeste已使用new进行实例化。切勿使用new实例化活动。
要么考虑是否需要其他活动，要么使用Intent来实例化，例如
Intent i = new Intent(MainActivity.this, ChartTeste.class);
startActivity(i);
答案 1 :(得分：0)
试试这个，
public String loadJSONFromAsset() {
String json = null;
try {
InputStream is = getAssets().open("file_name.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
return json;
}
这可能会对你有所帮助
答案 2 :(得分：0)
this
参考当前对象，我认为你应该使用
getApplicationContext()