Checking with if and else if there is a value in sharedpreference

I'm trying to check if there is a value in the shared preference, if not, an Alert Dialog with an EditText will be displayed to add the value.

More so far so good, and displayed and the value is inserted and saved.

More when the application is closed and opened again, it displays the dialog asking again for the value that is no longer assigned to Shared Preference

This is my code:

public void checkValue() {
SharedPreferences sp = getSharedPreferences("USERCODE", 0);
if (sp.getString("tag", "") != null)
{
openAlert();
}
else
{
Toast.makeText(getBaseContext(), "Existing value.", Toast.LENGTH_SHORT).show();
}
}
private void openAlert()
{
mValue = getSharedPreferences("PREFERENCE", MODE_PRIVATE).getBoolean("mValue", true);
if (mValue)
{
AlertDialog.Builder mAlertDialog = new AlertDialog.Builder(this);
final View customLayout = getLayoutInflater().inflate(R.layout.alert_dialog, null);
final EditText userInput = customLayout.findViewById(R.id.alertdialogEditTextCode);
mAlertDialog.setView(customLayout);
mAlertDialog.setCancelable(false);
mAlertDialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton)
{
String value = userInput.getText().toString();
SharedPreferences sp = getSharedPreferences("USERCODE", 0);
SharedPreferences.Editor preferencesEditor = sp.edit();
preferencesEditor.putString("tag", value);
preferencesEditor.commit();
updatdCode();
Toast.makeText(getBaseContext(), "Código salvo com sucesso!", Toast.LENGTH_SHORT).show();
dialog.dismiss();
}
});
mAlertDialog.show();
getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit().putBoolean("mValue", true).commit();
}
}
private void updatdCode()
{
SharedPreferences sp = getSharedPreferences("USERCODE", 0);
String data = sp.getString("tag", "");
mTextView = (TextView) findViewById(R.id.game_title);
mTextView.setText(data);
}
}

How can this be resolved?

The problem was solved, using a String and calling updatdCode (); at the beginning.

package com.vanderclin.app;
import android.app.*;
import android.content.*;
import android.os.*;
import android.view.*;
import android.widget.*;
import com.vanderclin.app.*;
public class MainActivity extends Activity 
{
private boolean mValue;
private TextView mTextView;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
SharedPreferences sp = this.getSharedPreferences("USERCODE", 0);
String usercode = sp.getString("CODE", "");
updatdCode();
if (usercode == "")
{
Toast.makeText(getBaseContext(), "User not registered.", Toast.LENGTH_LONG).show();
mValue = getSharedPreferences("PREFERENCE", MODE_PRIVATE).getBoolean("mValue", true);
if (mValue)
{
AlertDialog.Builder mAlertDialog = new AlertDialog.Builder(this);
final View customLayout = getLayoutInflater().inflate(R.layout.alert_dialog, null);
final EditText userInput = customLayout.findViewById(R.id.alertdialogEditTextCode);
mAlertDialog.setView(customLayout);
mAlertDialog.setCancelable(false);
mAlertDialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton)
{
String value = userInput.getText().toString();
SharedPreferences sp = getSharedPreferences("USERCODE", 0);
SharedPreferences.Editor preferencesEditor = sp.edit();
preferencesEditor.putString("CODE", value);
preferencesEditor.commit();
updatdCode();
Toast.makeText(getBaseContext(), "Code saved successfully!", Toast.LENGTH_SHORT).show();
dialog.dismiss();
}
});
mAlertDialog.show();
getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit().putBoolean("mValue", true).commit();
}
}
else
{
Toast.makeText(getBaseContext(), "Registered user.", Toast.LENGTH_LONG).show();
}
}
private void updatdCode()
{
SharedPreferences sp = getSharedPreferences("USERCODE", 0);
String data = sp.getString("CODE", "");
mTextView = findViewById(R.id.mainTextView);
mTextView.setText(data);
}
}```
</details>
# 答案1
**得分**: 1
```plaintext
sp.getString("tag", "")
这个结果永远不可能为null，因为如果在SharePreference中找不到，它会返回默认值，而默认值是您在第二个参数中声明的空字符串`""`。
所以您必须更改为
if (!sp.getString("tag", "").equals(""))

if (!sp.getString("tag", "").equals(""))

答案2

得分: 1

从Brian H.的回答中，我稍微修改了一下：

if (sp.getString("tag", "").equals("")) {
    openAlert();
}

默认值是 ""，因此您必须与空字符串进行比较。如果相等，那么意味着在共享首选项中没有值。

抱歉，我还不能发表评论。

if (sp.getString("tag", "").equals(""))
{
openAlert();
}