實例狀態未正確恢復/保存

Question

當屏幕方向改變時，我試圖保存和恢復一個布爾字段。 無論出於何種原因，該字段在第一次方向更改期間都正確保存/恢復，但是當方向更改回初始狀態時，調用onSaveInstanceState()時布爾值是錯誤的。

根據這個答案，我將android:configChanges="orientation"添加到清單中相應的活動標簽。 以下代碼包含相關方法，為清晰起見進行了簡化：

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);
    }
}

這是我開始活動並從縱向 -> 橫向然后從橫向 -> 縱向更改時的 Logcat 輸出：

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

編輯：問題原來是由我實現簽名板的事件處理程序引起的：

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;
        }
    });
}

所述onClear()之后方法被調用onRestoreInstanceState()並在標志設置為true 。 由於@SOreadytohelp 發布的解決方案回答了我最初的問題，因此我接受了他們的回答。

Answer 1

我在Github上創建了一個簡單的演示，向您展示如何存儲和恢復實例狀態，如果您理解它，請告訴我。 這是一個簡單的應用程序，有一個按鈕，當你按下按鈕時，你會改變布爾值的狀態，如果你旋轉屏幕，你仍然擁有與以前相同的值。 我希望是你正在尋找的。

他們的關鍵是在onRestoreInstanceState()獲取Boolean並在onSaveInstanceState()保存Boolean ，你不需要這個android:configChanges="orientation in the manifest.xml

@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);
}