Question

我试图在两个活动之间发送一个Intent值，尽管它看上去很象，已经读过this，但在我的第二个活动中，接收到的intent为null；在运行时加入了NPE。

其背后的预期功能是：“用户扫描活动A中的代码”->“接收到的真实值并打包到意图中”->“活动B打开，解开意图并检查意图值是否为true'->'如果为true，则活动中ImageView的高度减少一定的数量'。

因此，我不确定为什么要在活动B中将我的Intent接收为null，因为我希望进行此检查以便在活动打开时更新高度？

活动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();
}

活动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

在活动B中，您从Intent Extras中拉出QRMethod时遇到错字。您已在使用“ QRmethod”和“ QRMethod”设置了附加功能。

Answer 2

您可以使用：

在第一个活动（MainActivity页面）

Intent i = new Intent(MainActivity.this,SecondActivity.class); 
 i.putExtra("QRmethod","readComplete" );
then you can get it from your second activity by :

在第二个活动中（SecondActivity页面）

Intent intent = getIntent();
String YourtransferredData = intent.getExtras().getString("QRmethod");

Answer 3

在第二个活动中，您可以使用intent.getStringExtra()这样的方法来获取字符串值。

if (getIntent() != null){
   getIntent().getStringExtra("QRmethod") //this s your "readComplete" value
}

NullPointerException关于两个活动之间的意图

3 个答案: