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我正在开发一个应用程序并希望保存我的复选框选项的 obe 状态，但是当我尝试使用 SharedPreferences 类（第一次使用它）时，我得到一个空指针异常。我已经进行了几个小时的故障排除，但找不到解决方案。任何人都可以看看这个并告诉我有什么问题吗？完整的代码要长得多，但这是给我空指针异常的公园。我知道它与 SharedPreferences 有关。

package us.mattmccoy.meanfind;

//import java.util.Arrays;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.ClipData;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {


//saved data stuff needed
SharedPreferences preferences = this.getSharedPreferences("us.mattmccoy.meanfind", Context.MODE_PRIVATE); 
Editor edit = preferences.edit();
//private data using saved data
String autoclearKEY = "us.mattmccoy.meanfind.AUTOCLEAR";
boolean autoclear = preferences.getBoolean(autoclearKEY, false);

//normal private data
final Context con1 = this;
int dividend;String dataFixed;boolean tb;
private CheckBox myCBox, acBox;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    addListenerBoxes();
    if(autoclear == true){
        acBox.setChecked(true);
    }else{
        acBox.setChecked(false);
    }
}
//check box listeners
public void addListenerBoxes(){
    //instantiate boxes
    acBox = (CheckBox) findViewById(R.id.chex2);
    acBox.setOnClickListener(new OnClickListener() {

          @Override
          public void onClick(View v) {
                    //is acBox checked?
            if (((CheckBox) v).isChecked()) {
                edit.putBoolean(autoclearKEY, true).commit();
            }else{
                edit.putBoolean(autoclearKEY, false).commit();
            }
          }
    });
    myCBox = (CheckBox) findViewById(R.id.chex);

}

错误信息：

http://pastebin.com/5P2Mfwik

4

1 回答 1

1

更改此行

SharedPreferences preferences = this.getSharedPreferences("us.mattmccoy.meanfind", Context.MODE_PRIVATE);

至

SharedPreferences preferences; = this.getSharedPreferences("us.mattmccoy.meanfind", Context.MODE_PRIVATE);

并放

preferences = this.getSharedPreferences("us.mattmccoy.meanfind", Context.MODE_PRIVATE);

在onCreate()

Context您在建立它之前尝试使用它，onCreate()因此您正在NPE使用context. 您还需要移动这些行

Editor edit = preferences.edit();
boolean autoclear = preferences.getBoolean(autoclearKEY, false);

onCreate()在你初始化之后进入，否则你会preferences得到另一个NPE，因为直到你初始化它。所以它应该是这样的preferencesnull

public class MainActivity extends Activity {
//saved data stuff needed
SharedPreferences preferences;   //declare them
Editor edit;
//private data using saved data
String autoclearKEY = "us.mattmccoy.meanfind.AUTOCLEAR";
boolean autoclear;
        @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    SharedPreferences preferences; = this.getSharedPreferences("us.mattmccoy.meanfind",   Context.MODE_PRIVATE);
    Editor edit = preferences.edit();   //initialize them
    boolean autoclear = preferences.getBoolean(autoclearKEY, false);
    addListenerBoxes();
    if(autoclear == true){
        acBox.setChecked(true);
    }else{
        acBox.setChecked(false);
    }

如果这不能解决您的问题，请发布完整的 logcat

于 2013-05-10T23:27:58.317 回答