Question

我有问题。当有条目统计活动正常工作。但如果没有条目，则stast活动崩溃。请帮我。需要一些东西来阻止它。（我不是程序员，所以对我来说不容易）

package com.sudarmuthu.android.wt.activities;

import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import com.sudarmuthu.android.wt.R;
import com.sudarmuthu.android.wt.data.DBUtil;
import com.sudarmuthu.android.wt.data.Entry;

/**
 * Activity class to handle stats
 * 

public class EntriesStatsActivity extends Activity {


// for debugging
private static boolean D = true;
private static String TAG = "WT - EntriesStatsActivity";

private List<Entry> mEntries;

/* (non-Javadoc)
 * @see android.app.Activity#onCreate(android.os.Bundle)
 */
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.entry_stats);

    Bundle bundle = getIntent().getExtras();
    int typeId = bundle.getInt("typeId");

    if (D) Log.d(TAG, "Got type id: " + typeId);

    mEntries = DBUtil.fetchEntries(this, typeId, null);
    Entry firstEntry = mEntries.get(0);

    int count = mEntries.size();
    float sum = 0;
    float average = 0;

    float min = Float.parseFloat(firstEntry.getValue());
    float max = Float.parseFloat(firstEntry.getValue());

    // calculate
    for (Entry entry : mEntries) {
        float value = Float.parseFloat(entry.getValue());
        sum += value;

        if (value < min) {
            min = value;
        }

        if (value > max) {
            max = value;
        }
    }

    average = sum / count;

    // populate the values
    TextView statsCount = (TextView) findViewById(R.id.statsCount);
    statsCount.setText("" + count);

    TextView statsSum = (TextView) findViewById(R.id.statsSum);
    statsSum.setText("" + sum);

    TextView statsAverage = (TextView) findViewById(R.id.statsAverage);
    statsAverage.setText("" + average);

    TextView valueFrom = (TextView) findViewById(R.id.valueFrom);
    valueFrom.setText("" + min);

    TextView valueTo = (TextView) findViewById(R.id.valueTo);
    valueTo.setText("" + max);

}

}

Answer 1

如果没有条目，mEntries.size()等于0.所以当你做

时

average = sum / count;

除以0，抛出Arithmetic Exception（不能将数字除以0）。

Answer 2

您可能会收到空指针异常：

mEntries = DBUtil.fetchEntries(this, typeId, null);
if( mEntries == null ) {
   return;
}

如果没有条目，则活动崩溃

2 个答案: