Question

字符串stored中包含“1.0”。每次按下按钮，我想将其值增加0.5。但相反，我的输出变为“1.00.5”。我该如何解决这个问题？

 String stored = userspeed.getText().toString();
 String speedplus = stored + 0.5;
 SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
 SharedPreferences.Editor editor = preferences.edit();
 editor.putString("user_speed", speedplus.toString());
 editor.apply();

更新

public class ProgramActivity extends AppCompatActivity {
    EditText userspeed;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_program);
        userspeed = (EditText) findViewById(R.id.userspeed);

        //load values
        SharedPreferences preferences = PreferenceManager
                .getDefaultSharedPreferences(getBaseContext());
        String stored = preferences.getString("user_speed", "1.0");//default
        userspeed.setText(stored, TextView.BufferType.EDITABLE);

    }

    public void adduserspeed(View view) {
        String stored = userspeed.getText().toString();
        double storedValue = Double.parseDouble(stored);
        String speedplus = String.valueOf(storedValue +0.5f);
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
        SharedPreferences.Editor editor = preferences.edit();
        editor.putString("user_speed", speedplus);
        editor.apply();
    }
}

Answer 1

    String stored = userspeed.getText().toString();
    float speedplus = Float.parseFloat(stored) + 0.5;
    SharedPreferences preferences = PreferenceManager
            .getDefaultSharedPreferences(this);
    SharedPreferences.Editor editor = preferences.edit();
    editor.putFloat("user_speed", speedplus);
    editor.apply();

将字符串值解析为int，然后进行数学运算。否则将发生字符串连接。

Answer 2

尝试解析存储的，即1.0为Double，然后添加0.5d

String speedplus = String.valueOf((Double.parseDouble(stored) + 0.5d));

最终代码

String stored = userspeed.getText().toString();
String speedplus = String.valueOf((Double.parseDouble(stored) + 0.5d));
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("user_speed", speedplus.toString());
editor.apply();

Answer 3

最快的黑客将是：

String speedplus = String.valueOf(Float.parseFloat(stored) + 0.5F);

但是，您的下一个问题无疑将是“为什么我的结果为1.499999999？”，即answered here in detail。

Answer 4

你也可以使用double：

 String speedplus = (Double.parseDouble(stored)+0.5).toString();

Answer 5

首先，您需要将字符串值转换为浮点值，然后执行添加操作，最后将结果转换为字符串，以便您可以在共享首选项中存储为字符串。

    final String stored = userspeed.getText().toString();
    final float storedValue = Float.parseFloat(stored);
    final String speedplus = String.valueOf(storedValue + 0.5f);
    final SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
    final SharedPreferences.Editor editor = preferences.edit();
    editor.putString("user_speed", speedplus);
    editor.apply();

如果要使用double值，只需将第一行替换为以下内容：

final String stored = "1.0";
final double storedValue = Double.parseDouble(stored);
final String speedplus = String.valueOf(storedValue + 0.5d);

<强>更新您的问题是在adduserspeed(View view)方法中，您没有从首选项中检索存储的值，您正在从EditText中检索，并且您没有更新该EditText值，因此每次执行adduserspeed(View view)方法时，您在首选项上存储的值是1.0 + 0.5，因为您重新打开应用程序之前EditText值为1.0。当您重新打开应用程序时，您的EditText值为1.5，依此类推......

我已经改进了你的代码，现在效果很好，不管怎么说，不要只是复制我的代码，尝试理解它，这样你就可以学习。

public class MainActivity extends AppCompatActivity {
private EditText userSpeed;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    this.userSpeed = (EditText) findViewById(R.id.userspeed);
    setUserSpeedText();

}

public void adduserspeed(View view) {
    final String stored = getUserSpeedValue();
    final double storedValue = Double.parseDouble(stored);
    final String speedPlus = String.valueOf(storedValue + 0.5f);
    setUserSpeedValue(speedPlus);
    setUserSpeedText();
}

private String getUserSpeedValue() {
    final SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
    return preferences.getString("user_speed", "1.0");
}

private void setUserSpeedValue(final String newSpeedValue) {
    final SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
    final SharedPreferences.Editor editor = preferences.edit();
    editor.putString("user_speed", newSpeedValue);
    editor.apply();
}

private void setUserSpeedText() {
    if (null != this.userSpeed) {
        this.userSpeed.setText(getUserSpeedValue());
    }
}
}

如何更改字符串的值？

5 个答案: