android - 实例状态未正确恢复/保存

Question

我正在尝试在屏幕方向发生变化时保存和恢复 bool 字段。无论出于何种原因，该字段在第一次方向更改期间正确保存/恢复，但当方向更改回初始状态时，调用 onSaveInstanceState() 时 bool 值是错误的。

根据 this answer ，我将 android:configChanges="orientation" 添加到 list 中相应的 Activity 标签。以下代码包含相关方法，为清楚起见进行了简化:

public class SignatureActivity extends AppCompactActivity {
    private boolean signaturePadIsEmpty = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        String orientation = getResources().getConfiguration().orientation == ORIENTATION_PORTRAIT ? "portrait" : "landscape";
        Log.d(TAG, "onCreate: Orientation is " + orientation + ", signaturePadIsEmpty = " + signaturePadIsEmpty);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        signaturePadIsEmpty = savedInstanceState.getBoolean("SignaturePadIsEmpty");

        String orientation = getResources().getConfiguration().orientation == ORIENTATION_PORTRAIT ? "portrait" : "landscape";
        Log.d(TAG, "onRestoreInstanceState: Orientation is " + orientation + ", signaturePadIsEmpty = " + signaturePadIsEmpty);
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBoolean("SignaturePadIsEmpty", signaturePadIsEmpty);

        String orientation = getResources().getConfiguration().orientation == ORIENTATION_PORTRAIT ? "portrait" : "landscape";
        Log.d(TAG, "onSaveInstanceState: Orientation is " + orientation + ", signaturePadIsEmpty = " + signaturePadIsEmpty);
    }
}

这是我开始 Activity 并从纵向 -> 横向然后从横向 -> 纵向更改时的 Logcat 输出:

06-27 11:50:08.037 32656-32656/com.example.www.debug D/SignatureActivity: onCreate: Orientation is portrait, signaturePadIsEmpty = true
06-27 11:50:12.405 32656-32656/com.example.www.debug D/SignatureActivity: onSaveInstanceState: Orientation is landscape, signaturePadIsEmpty = false
06-27 11:50:12.461 32656-32656/com.example.www.debug D/SignatureActivity: onCreate: Orientation is landscape, signaturePadIsEmpty = true
06-27 11:50:12.465 32656-32656/com.example.www.debug D/SignatureActivity: onRestoreInstanceState: Orientation is landscape, signaturePadIsEmpty = false
06-27 11:50:15.068 32656-32656/com.example.www.debug D/SignatureActivity: onSaveInstanceState: Orientation is portrait, signaturePadIsEmpty = true
06-27 11:50:15.131 32656-32656/com.example.www.debug D/SignatureActivity: onCreate: Orientation is portrait, signaturePadIsEmpty = true
06-27 11:50:15.133 32656-32656/com.example.www.debug D/SignatureActivity: onRestoreInstanceState: Orientation is portrait, signaturePadIsEmpty = true

编辑:问题原来是由我执行签名板的事件处理程序引起的:

private void initializeLayoutElements(final int orientation) {
    signaturePad = findViewById(R.id.signature_pad);
    signaturePad.setOnSignedListener(new SignaturePad.OnSignedListener() {
        @Override
        public void onStartSigning() {
            signaturePadIsEmpty = false;
        }

        @Override
        public void onSigned() {
        }

        @Override
        public void onClear() {
            signaturePadIsEmpty = true;
        }
    });
}

onClear() 方法在 onRestoreInstanceState() 之后调用，并将标志设置为 true。由于@SOreadytohelp 发布的解决方案回答了我最初的问题，我接受他们的回答。

Answer 1

我在 Github 上创建了一个简单的演示向您展示如何存储和恢复实例状态，如果您理解，请告诉我。这是一个简单的应用程序，有一个按钮，当您按下按钮时，您会更改 bool 值的状态，如果您旋转屏幕，您仍然拥有与以前相同的值。我希望是您正在寻找的东西。

它们的关键是在 onRestoreInstanceState() 中获取 Boolean 并在 onSaveInstanceState() 中保存 Boolean 和你不需要 manifest.xml

中的这个 android:configChanges="orientation

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    signaturePadIsEmpty = savedInstanceState.getBoolean("SignaturePadIsEmpty");
    tvState.setText(String.valueOf(signaturePadIsEmpty));

}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putBoolean("SignaturePadIsEmpty", signaturePadIsEmpty);
}