Question

我的代码中标有/ Here /的行上出现空指针异常。我花了大约2个小时查找AssetManager以及如何使用它等，但仍然无法弄清楚为什么它是null。我已经从上下文和资源中调用了getAssets（），但我仍然是null。有人可以帮我从这里出去吗？感谢。

package com.hamc17.CatFacts;

import android.app.Activity;
import android.content.Context;
import android.content.res.AssetManager;
import android.content.res.Resources;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Random;

public class FactsActivity extends Activity{

Context context;
Resources res;

@Override
public void onCreate(Bundle savedInstanceBundle){

    super.onCreate(savedInstanceBundle);

    context = getApplicationContext();
    res = context.getResources();

    Button getFactButton = (Button) findViewById(R.id.getFactButton);
    getFactButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Toast toastMessageOnClick = new Toast(FactsActivity.this);
            toastMessageOnClick.setText(getFact());
            if((toastMessageOnClick.toString()).length()>50)
            {
                toastMessageOnClick.setDuration(10);
            }
            else
            {
                toastMessageOnClick.setDuration(Toast.LENGTH_LONG);
            }
            toastMessageOnClick.show();
        }
    });
}


    String[] factArray = getFactsFromTextFile().split(";");
    private String getFactsFromTextFile(){
/*Here*/ AssetManager assMan = context.getAssets();
        try{
            BufferedReader buff = new BufferedReader(new InputStreamReader(assMan.open("facts.txt")));
            String line;
            StringBuilder build = new StringBuilder();
            while((line = buff.readLine()) != null)
            {
                build.append(line).append(System.getProperty("line.seperator"));
            }
            return build.toString();
        }
        catch (IOException e)
        {
            Toast toastMessage = new Toast(getApplicationContext());
            toastMessage.setText(e.toString() + "\n Whoops, there was an error! ");
            toastMessage.show();
            return "";
        }
        finally
        {
            try{
                assMan.close();
            }
            catch (Exception e)
            {
                //Whatever Trevor
            }
        }
    }

private String getFact(){

    String randomFactString = "";
    int factCount = factArray.length;

    Random rng = new Random();
    int randomNum = rng.nextInt()*factCount;

    randomFactString = factArray[randomNum];

    return randomFactString;
}

}

Answer 1

您缺少setContentView(R.layout.mylayout);

@Override
public void onCreate(Bundle savedInstanceBundle){
    super.onCreate(savedInstanceBundle);
    setContentView(R.layout.mylayout);
    Button getFactButton = (Button) findViewById(R.id.getFactButton);

findViewById查找当前膨胀布局中具有id的资源。因此，您应该在初始化视图之前将布局的内容设置为活动

您也可以使用

res = getResources();

Answer 2

而不是创建一个局部变量来获取Activity的Context只需使用getBaseContext（）;每次要获取Context的引用。

所以这样的话：

AssetManager assMan = getBaseContext().getAssets();

AssetManager空指针异常

2 个答案: