Question

我试图从另一个类更新我的TextView，但它一直在崩溃。

最初说＆＃34;应用已被锁定＆＃34;，并将用户带到下一个输入密码的布局。
当用户输入正确的密码时，应用程序会将用户转到上一个，并且textview已更改说“＃34;应用程序现已解锁！＆＃34;

MainActivity：

public class MainActivity extends AppCompatActivity {


private Button login;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    login = (Button)findViewById(R.id.btn);

    login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            confirm(login.toString());

        }
    });
}
private void confirm(String s){
        Intent intent = new Intent(MainActivity.this, SecondActivity.class);
        startActivity(intent);
    }
}

第二项活动：

public class SecondActivity extends AppCompatActivity implements 
View.OnClickListener {
public boolean first = false;
public boolean second = false;
public boolean third = false;
public boolean fourth = false;
public boolean submit = false;
public TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);

    Button first = (Button) findViewById(R.id.btn1);
    first.setOnClickListener(this);
    Button second = (Button) findViewById(R.id.btn2);
    second.setOnClickListener(this);
    Button third = (Button) findViewById(R.id.btn3);
    third.setOnClickListener(this);
    Button fourth = (Button) findViewById(R.id.btn4);
    fourth.setOnClickListener(this);
    Button submit = (Button) findViewById(R.id.submit);
    submit.setOnClickListener(this);
    textView = (TextView)findViewById(R.id.text);




}
    public int counter;

    public void onClick(View v) {

        counter++;
        switch (v.getId()) {

            case R.id.btn1:
                if (counter == 1) {
                    first = true;
                }
                break;
            case R.id.btn2:
                if (counter == 2) {
                    second = true;
                }
                break;
            case R.id.btn3:
                if (counter == 3) {
                    third = true;
                }
                break;
            case R.id.btn4:
                if (counter == 4) {
                    fourth = true;
                }
                break;
            case R.id.submit:
                submit = true;
                open();
                break;
        }

    }



    public void open() {
        if (first && second && third && fourth && submit) {
            textView.setText("Your App is now Unlocked!");
            Intent intent = new Intent(SecondActivity.this, 
MainActivity.class);
            startActivity(intent);
            finish();



        } else {
            Intent intent = new Intent(SecondActivity.this, 
MainActivity.class);
            startActivity(intent);
            finish();

        }


    }


}

MainActivity布局：

<Button
    android:id="@+id/btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginTop="8dp"
    android:text="unlock"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginTop="8dp"
    android:text="Welcome to the app! The app is LOCKED!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.238" />

</android.support.constraint.ConstraintLayout>

Answer 1

确保所有活动都在清单中。
确保所有XML元素都在正确的布局中。例如，android:id="@+id/text"不是activity_second.xml的一部分，因此它为空。

通常，您错误地传递Intent对象。你有一个周期。

MainActivity启动第二个

private void confirm(String s){
    Intent intent = new Intent(MainActivity.this, SecondActivity.class);
    startActivity(intent);
}

然后开始Main

Intent intent = new Intent(SecondActivity.this, 
MainActivity.class);
startActivity(intent);

你可以继续以这种方式将Activity实例添加到堆栈中。

您需要做的是How to manage `startActivityForResult` on Android?

Getting a Result from an Activity。

首先，你可以试试这个

public static final int CONFIRM_RESULT = 1;

private void confirm(String s){
    Intent intent = new Intent(MainActivity.this, SecondActivity.class);
    intent.putExtra("passphrase", s);
    startActivityForResult(intent, CONFIRM_RESULT);
}

如何从其他类更新TextView？

1 个答案: