Question

我一直在尝试创建一个应用程序，用户可以在其中设置语言并将其存储在共享首选项中。用户可以通过菜单进一步更改首选项。语言首选项将显示在文本视图中。

但是，当我单击任何选项时，应用程序便崩溃了。

Logcat：-

Process: com.example.alertdemo, PID: 6678
java.lang.NullPointerException: Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences.edit()' on a null object reference
    at com.example.alertdemo.MainActivity.setLanguage(MainActivity.java:24)
    at com.example.alertdemo.MainActivity$2.onClick(MainActivity.java:64)
    at androidx.appcompat.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6715)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:911)

这是代码：

package com.example.alertdemo;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.content.DialogInterface;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {


 SharedPreferences sharedPreferences;
 public void setLanguage(String language){
     sharedPreferences.edit().putString("language", language).apply();
     TextView textView = (TextView) findViewById(R.id.textView1);
     textView.setText(language);
 }
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater menuInflater = getMenuInflater();
    menuInflater.inflate(R.menu.main_menu, menu);
    return super.onCreateOptionsMenu(menu);

}

@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
    switch (item.getItemId()){
        case R.id.English:
            setLanguage("English");
            return true;
        case R.id.Spanish:
            setLanguage("Spanish");
            return true;
        default:
            return false;
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    this.getSharedPreferences("com.example.alertdemo", Context.MODE_PRIVATE);

    new AlertDialog.Builder(this)
            .setIcon(android.R.drawable.ic_dialog_alert)
            .setTitle("Choose Language")
            .setMessage("Choose your Language")
            .setPositiveButton("English", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    setLanguage("English");
                }
            })
            .setNegativeButton("Spanish", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    setLanguage("Spanish");
                }
            }).show();



}
}

Answer 1

尝试一下。

     public void setLanguage(String language)
{
         SharedPreferences sharedPreferences = getSharedPreferences("name", Context.MODE_PRIVATE);
         sharedPreferences.edit().putString("language", language).apply();
         TextView textView = (TextView) findViewById(R.id.textView1);
         textView.setText(language);
}

尝试在空对象引用上

1 个答案: