我已经在这个项目上工作了几天，我无法弄清楚它为什么会一直崩溃。该项目是获取一个位于assets文件夹中的文件，其中包含一堆双打（使用包含文件名的用户的输入），找到它们的余弦，并显示结果供用户查看。这是我的MainActivity类：
package com.example.brandon.lab1;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.TextView;
import android.os.StrictMode;
import android.content.res.AssetManager;
import java.util.Scanner;
import java.util.ArrayList;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.io.IOException;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void cosAndDisplay(View view)
throws IOException {
EditText et;
TextView tv;
int numOfItems;
String fileName;
tv = (TextView) findViewById(R.id.text_main);
et = (EditText) findViewById(R.id.edit_infile);
fileName = (et.getText().toString());
AssetManager assetManager = getAssets();
Scanner fsc = new Scanner(assetManager.open(fileName));
ArrayList<Double> nums = new ArrayList<>();
while (fsc.hasNextDouble()) {
String[] line = fsc.nextLine().split(" ");
for (String s : line) {
nums.add(Double.parseDouble(s));
}
}
fsc.close();
numOfItems = nums.size();
cos_it(nums, numOfItems);
ArrayList<String> numList = new ArrayList<>();
for (int x = 0; x < numOfItems; x++) {
numList.add(nums.get(x).toString());
}
NumberFormat formatter = new DecimalFormat("#0.00");
for (int y = 0; y < numOfItems; y++) {
tv.setText(formatter.format(numList.get(y)));
}
}
public static void cos_it(ArrayList<Double> a, int num_items) {
for(int x=0; x<=num_items; x++) {
a.set(x, Math.cos(a.get(x)));
}
}
}
这是崩溃报告：
--------- beginning of crash
10-10 16:02:25.649 3009-3009/com.example.brandon.lab1 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.brandon.lab1, PID: 3009
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
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$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
at java.util.ArrayList.get(ArrayList.java:308)
at com.example.brandon.lab1.MainActivity.cos_it(MainActivity.java:104)
at com.example.brandon.lab1.MainActivity.cosAndDisplay(MainActivity.java:88)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
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)
10-10 16:02:28.687 3009-3009/? I/Process: Sending signal. PID: 3009 SIG: 9
答案 0 :(得分：0)
如logcat中所指定的那样，你得到了一个
引起：java.lang.IndexOutOfBoundsException：索引0无效，大小为0
从 cos_it 方法中，其中ArrayList的输入参数大小为0，这意味着它不包含任何项目。
如果正确填充了所需的ArrayList，则需要进行调试。