java - Android程序问题，NullPointerExc

Question

嗯，我的程序一直给我一个空点异常，我不知道为什么？我知道它与lvl变量有关，但我不知道是什么？我该如何解决这个问题？

日志猫:

03-18 16:14:55.852: ERROR/AndroidRuntime(277): FATAL EXCEPTION: main
03-18 16:14:55.852: ERROR/AndroidRuntime(277): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.games.think/com.games.think.Think}: java.lang.NullPointerException
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.os.Looper.loop(Looper.java:123)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread.main(ActivityThread.java:4627)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at java.lang.reflect.Method.invokeNative(Native Method)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at java.lang.reflect.Method.invoke(Method.java:521)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at dalvik.system.NativeStart.main(Native Method)
03-18 16:14:55.852: ERROR/AndroidRuntime(277): Caused by: java.lang.NullPointerException
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at com.games.think.Think.onCreate(Think.java:38)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
03-18 16:14:55.852: ERROR/AndroidRuntime(277):     ... 11 more

这是我的一些代码:

     package com.games.think;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;

public class Think extends Activity implements OnClickListener{

    int question = 1, lvl;

    /** Called when the activity is first created. */
    RadioButton lvl1;
    RadioButton lvl2;
    RadioButton lvl3;
    RadioButton lvl4;
    RadioButton lvl5;


    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button play = (Button)findViewById(R.id.play);
        play.setOnClickListener(this);
        Button level = (Button)findViewById(R.id.level);
        level.setOnClickListener(this);
        Button exit = (Button)findViewById(R.id.exit);
        exit.setOnClickListener(this);
        Button setLevel = (Button)findViewById(R.id.setLevel);
        setLevel.setOnClickListener(this);
        lvl1 = (RadioButton)findViewById(R.id.lvl1);
        lvl2 = (RadioButton)findViewById(R.id.lvl2);
        lvl3 = (RadioButton)findViewById(R.id.lvl3);
        lvl4 = (RadioButton)findViewById(R.id.lvl4);
        lvl5 = (RadioButton)findViewById(R.id.lvl5);

        lvl = getLevel();
        if(lvl == -1) {
            lvl=getLevel();
        }


    }

    @SuppressWarnings("null")
    private int getLevel() {

        String FILENAME = "think_level";
        FileInputStream fis;
        byte[] buffer = new byte[1000];



        try {
            fis = openFileInput(FILENAME);
        } catch (FileNotFoundException e) {
            setLevel("1");
            return -1;
        }

        try {
            fis.read(buffer,0,1000);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            fis.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String level = buffer.toString();
        int iLevel = Integer.valueOf(level);
        return iLevel;
    }

    private void setLevel(String level) {
        String FILENAME = "think_level";
        String string = level;

        FileOutputStream fos;
        try {
            fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
            fos.write(string.getBytes());
            fos.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }

    }

    @Override
    public void onClick(View v) {
        switch( v.getId()){
        case R.id.play:
            setContentView(R.layout.play);
            setQuestion();
        case R.id.level:
            setContentView(R.layout.level);
            switch(getLevel()) {
            case 1:
                lvl1.setChecked(true);
            case 2:
                lvl2.setChecked(true);
            case 3:
                lvl3.setChecked(true);
            case 4:
                lvl4.setChecked(true);
            case 5:
                lvl5.setChecked(true);

            }

        case R.id.setLevel:
            if(lvl1.isChecked()) {
                setLevel("1");
            }
            if(lvl2.isChecked()) {
                setLevel("2");
            }
            if(lvl3.isChecked()) {
                setLevel("3");
            }
            if(lvl4.isChecked()) {
                setLevel("4");
            }
            if(lvl5.isChecked()) {
                setLevel("5");
            }







        }
    }

    private void setQuestion() {




    }



    }

Answer 1

检查 ID 为“setLevel”的按钮是否在您的 main.xml 中。如果在其他地方，你找不到它，如下所示:

 Button setLevel = (Button)findViewById(R.id.setLevel);

但是你需要一个充气机。