java - 两个 Activity 之间的 Intent 出现 NullPointerException

Question

我正在尝试在两个 Activity 之间发送一个 Intent 值，尽管看起来已经阅读了 this ，在我的第二个 Activity 中，收到的 Intent 是空的；在运行时遇到 NPE。

这背后的预期功能是:“用户在 Activity A 中扫描代码”->“收到真实值并将其打包到 intent 中”->“Activity B 打开、解压缩 intent 并检查 intent 值是true' -> '如果为 true， Activity 中 ImageView 的高度将减少一个设定的量'。

因此，我不确定为什么我的 Intent 在 Activity B 中被接收为 null，因为我希望进行此检查以便在 Activity 打开时更新高度？

Activity A:

//do the handling of the scanned code being true and display 
//a dialog message on screen to confirm this 
@Override
public void handleResult(Result result) {
    final String myResult = result.getText();
    Log.d("QRCodeScanner", result.getText());
    Log.d("QRCodeScanner", result.getBarcodeFormat().toString());

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle("Activity Complete!");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
        //the user has pressed the OK button
        @Override
        public void onClick(DialogInterface dialog, int which) {
            scannerView.resumeCameraPreview(QRActivity.this);
            //pack the intent and open our Activity B
            Intent intent = new Intent(QRActivity.this, ActivityTank.class);
            intent.putExtra("QRMethod", "readComplete");
            startActivity(intent);

        }
    });

    builder.setMessage(result.getText());
    AlertDialog alert1 = builder.create();
    alert1.show();
}

Activity B:

// in onCreate, I check that the bundled intent is true
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_tank);

    if (savedInstanceState == null) {
        Bundle extras = getIntent().getExtras();
        if (extras == null) {
            //then the extras bundle is null, and nothing needs to be called here
        }
        else {
            String method = extras.getString("QRmethod");

            if (method.equals("readComplete")) {
                updateTank();
            }
        }
    }
}

//this is the method that is called when the intent check is true

public int tHeight = 350;

public void updateTank() {
    ImageView tankH = (ImageView)findViewById(R.id.tankHeight);
    ViewGroup.LayoutParams params = tankH.getLayoutParams();
    params.height = tHeight - 35;
    tankH.setLayoutParams(params);
    }

Answer 1

在 Activity B 中，您在从 Intent extras 中提取 QRMethod 时出现错字。您正在使用 QRmethod，而您已经使用“QRMethod”设置了附加功能。