英文:
Wrong calculation after using sharedpreferences
问题
我正在构建一个应用程序，用于检查素数并显示它们。用户需要能够保存数字并在应用程序重新启动时加载它。
当从Sharedprefrences中检索保存的整数时，我遇到问题。代码保存整数并在“loaddata”函数中加载它。但是当我开始检查保存的数字是否是素数时，代码会跳过2个素数。例如，如果我保存“11”，下一个素数应该是“13”，但它跳到了“19”。
如果有人能指导我一下，那将非常好，因为我有点新手。
public class MainActivity extends AppCompatActivity {
private TextView textView;
private EditText editText;
private Button applyPrimeButton;
private Button saveButton;
private Button loadButton;
public static final String SHARED_PREFS = "sharedPrefs";
int max = 500;
int j = 2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textview);
editText = (EditText) findViewById(R.id.edittext);
applyPrimeButton = (Button) findViewById(R.id.apply_prime_button);
saveButton = (Button) findViewById(R.id.save_button);
loadButton = (Button) findViewById(R.id.load_button);
applyPrimeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
for (int i = j; i <= max; i++) {
if (isPrimeNumber(i)) {
textView.setText(i + "");
j = i + 1;
break;
}
}
}
});
saveButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
saveData();
}
});
loadButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
loadData();
}
});
}
public boolean isPrimeNumber(int nummer) {
for (int i = 2; i <= nummer / 2; i++) {
if (nummer % i == 0) {
return false;
}
}
return true;
}
public void saveData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
int nummer = Integer.parseInt(textView.getText().toString());
editor.putInt("prime_save", nummer);
editor.commit();
Toast.makeText(this, "Data saved", Toast.LENGTH_SHORT).show();
}
public void loadData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
int nummer = sp.getInt("prime_save", 0);
textView.setText(String.valueOf(nummer));
}
}
希望这可以帮助你解决问题。
英文:
I'm building an app to check prime numbers and display them. the user need to be able to save the number and load it upon restart of the app.
I have problem when retrieving the saved int from Sharedprefrences. the codes saves the int and loads it on the "loaddata" function. But when I start checking if the saved in is a primenumber, the code jumps 2 primenumbers. Eg if I save "11", the next primenumber should be "13" but it jumps to "19".
Would be great if someone could point into the right direction since i'm a bit of newbie.
public class MainActivity extends AppCompatActivity {
private TextView textView;
private EditText editText;
private Button applyPrimeButton;
private Button saveButton;
private Button loadButton;
public static final String SHARED_PREFS = "sharedPrefs";
int max = 500;
int j = 2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textview);
editText = (EditText) findViewById(R.id.edittext);
applyPrimeButton = (Button) findViewById(R.id.apply_prime_button);
saveButton = (Button) findViewById(R.id.save_button);
loadButton = (Button) findViewById(R.id.load_button);
applyPrimeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
for (int i = j; i <= max; i++) {
if (isPrimeNumber(i)) {
textView.setText(i+"");
j = i+1;
break;
}
}
}
});
saveButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
saveData();
}
});
loadButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
loadData();
}
});
}
public boolean isPrimeNumber(int nummer) {
for (int i = 2; i <= nummer / 2; i++) {
if (nummer % i == 0) {
return false;
}
}
return true;
}
public void saveData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
int nummer = Integer.parseInt(textView.getText().toString());
editor.putInt("prime_save", nummer);
editor.commit();
Toast.makeText(this, "Data saved", Toast.LENGTH_SHORT).show();
}
public void loadData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
int nummer = sp.getInt("prime_save",0);
textView.setText(String.valueOf(nummer));
}
}
答案1
得分: 0
几个问题：
- 当加载数据时，您没有将 j 更新为正确的值，而是依赖于您在文本视图中显示的内容。
- 要找到素数，只需要检查原始数字的平方根，而不是它的一半。
尝试这样做：
applyPrimeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (j < max) {
if (isPrimeNumber(j)) {
textView.setText(j + "");
j++;
}
}
}
});
public void saveData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putInt("prime_save", j);
editor.commit();
Toast.makeText(this, "数据已保存", Toast.LENGTH_SHORT).show();
}
public void loadData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
int nummer = sp.getInt("prime_save", 0);
j = nummer;
textView.setText(String.valueOf(nummer));
}
注意：我保留了变量和方法名称的原始拼写，因为这些是代码的一部分。
英文:
Several issues:
- You are not updating j to the correct value when loading data, and instead relying on what you are displaying in the textview.
- To find prime number, it is enough to check until the square root of the original number and not half of it.
Try this:
applyPrimeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(j<max ){
if (isPrimeNumber(j)) {
textView.setText(j+"");
j++;
}
}
}
});
public void saveData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putInt("prime_save", j);
editor.commit();
Toast.makeText(this, "Data saved", Toast.LENGTH_SHORT).show();
}
public void loadData() {
SharedPreferences sp = getSharedPreferences(SHARED_PREFS, Activity.MODE_PRIVATE);
int nummer = sp.getInt("prime_save",0);
j = nummer;
textView.setText(String.valueOf(nummer));
}
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