如何使用“`onSaveInstanceState`”？

Question

我想实现什么？

• 我想保存x、y和score的值，所以当用户旋转屏幕时，这些值就会被检索，而不是重新生成。

​

​

我有什么？

1. 可能会纠正不起作用的onSaveInstanceState代码--可能是因为某些@Override与其发生冲突--

我需要什么？

帮助我保存变量的值(

)的一些修正

代码

无onSaveInstanceState**)** ( MainActivity.java )

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    private EditText textBox;
    private int z;
    public int score = 0;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ((TextView) findViewById(R.id.scoreText)).setText(R.string.nullScore);
        textBox = findViewById(R.id.editText);
        textBox.requestFocus();
        setActual();
    }

    private void setActual() {
        Random random = new Random();
        int x = random.nextInt(10) + 1; //you get a random number between 0 and 9 then add 1 to get 1 - 10, no need to use array..
        int y = random.nextInt(10) + 1;
        z = x * y;
        String hintStr = x + " × " + y;
        ((TextView) findViewById(R.id.hintTextView)).setText(hintStr);
    }


            public void onCheck(View view) {

        int answer = Integer.parseInt(textBox.getText().toString());
        String res = "Incorrect";
        if (answer == z) {
            res = "Correct";
            score++;
            Log.d("TAG", "Correct."); // right answer
            textBox.setText("");
            setActual(); // let's regenerate values
        } else if (score == 0) {
            Log.d("TAG", "Incorrect."); // wrong answer
            textBox.setText("");
            setActual();
            ((TextView) findViewById(R.id.scoreText)).setText(R.string.nullScore);
        } else {
            Log.d("TAG", "Incorrect."); // wrong answer
            textBox.setText("");
            score--;
            setActual();
        }
        ((TextView) findViewById(R.id.scoreText)).setText("Score:" + ' ' + score);
        ((TextView) findViewById(R.id.result_text_view)).setText(res);
    }

}

onSaveInstanceState**)** MainActivity.java (与MainActivity.java)

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    private EditText textBox;
    private int z;
    public int score = 0;
    private int x;
    private int y;

    public void onSaveInstanceState(Bundle savedInstanceState) {
        savedInstanceState.putInt("x", x);
        savedInstanceState.putInt("y", y);
        savedInstanceState.putInt("score", score);
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textBox = findViewById(R.id.editText);
        textBox.requestFocus();
        setActual();
        if (savedInstanceState != null) {
            x = savedInstanceState.getInt("x");
            y = savedInstanceState.getInt("y");
            score = savedInstanceState.getInt("score");
        }
    }

    private void setActual() {
        Random random = new Random();
        x = random.nextInt(10) + 1; //you get a random number between 0 and 9 then add 1 to get 1 - 10, no need to use array..
        y = random.nextInt(10) + 1;
        z = x * y;
        String hintStr = x + " × " + y;
        ((TextView) findViewById(R.id.hintTextView)).setText(hintStr);
    }


            public void onCheck(View view) {

        int answer = Integer.parseInt(textBox.getText().toString());
        String res = "Incorrect";
        if (answer == z) {
            res = "Correct";
            score++;
            Log.d("TAG", "Correct."); // right answer
            textBox.setText("");
            setActual(); // let's regenerate values
        } else if (score == 0) {
            Log.d("TAG", "Incorrect."); // wrong answer
            textBox.setText("");
            setActual();
            ((TextView) findViewById(R.id.scoreText)).setText(R.string.nullScore);
        } else {
            Log.d("TAG", "Incorrect."); // wrong answer
            textBox.setText("");
            score--;
            setActual();
        }
        ((TextView) findViewById(R.id.scoreText)).setText("Score:" + ' ' + score);
        ((TextView) findViewById(R.id.result_text_view)).setText(res);
    }

}

Answer 1

您应该考虑调用super.onSaveInstanceState()

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    // save your state
    super.onSaveInstanceState(outState);
}

此外，为了避免每次屏幕旋转时重新创建活动，您可以通过将此添加到应用程序清单中的活动声明中来自行处理配置更改：

android:configChanges="keyboardHidden|orientation|screenSize"

并推翻：

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
}

如果您的应用程序不需要在定位或screenSize更改后重新创建，它可以为用户节省时间.

Answer 2

确实没有检索值吗？我认为这里的问题是，您总是在setActual()中调用onCreate()，它生成x和y值，并将z值赋值给生成的x和y(即使savedInstanceState != null)。

处理事情的更好方法是

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textBox = findViewById(R.id.editText);
    textBox.requestFocus();

    if (savedInstanceState != null) {
        x = savedInstanceState.getInt("x");
        y = savedInstanceState.getInt("y");
        score = savedInstanceState.getInt("score");
        z = x * y;
        String hintStr = x + " × " + y;
        ((TextView) findViewById(R.id.hintTextView)).setText(hintStr);
    } else { setActual(); }
}

您还应该像这样调用super.onSaveInstanceState(savedInstanceState)

@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    savedInstanceState.putInt("x", x);
    savedInstanceState.putInt("y", y);
    savedInstanceState.putInt("score", score);
}