java - 在投票应用程序的 Activity 之间传递数据

Question

我是 android 编程的新手，遇到了一个问题。我正在尝试创建一个投票应用程序，当用户打开应用程序并显示 MainActivity 时，他们从这里按下一个按钮进入第二个屏幕 (Screen2)，该屏幕将人物图像及其名称显示为按钮。当一个人的名字(在 Screen2 的按钮中)被按下时，一个文本字段显示按钮在另一个 Activity (Screen4)中被按下的次数。这里的问题是，当我尝试显示这个 (Screen4) 时，应用程序崩溃了。我对此很陌生，所以如果您不理解我的问题或需要更多信息，请告诉我。任何帮助表示赞赏。谢谢。

编辑:经过一些帮助后，我使用 Intent 尝试发送数据，但现在当按下 screen2 中的按钮时，应用程序会刷新，然后将我带回 mainActivity，当再次尝试此过程时，应用程序会崩溃。

这是新的 Screen2:

package com.example.myapplication1;

import androidx.appcompat.app.AppCompatActivity;


import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class Screen2 extends AppCompatActivity {

    TextView showValue;
    int counter = 0;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_screen2);

        showValue = findViewById(R.id.VoteCountAnnie);//VoteCountAnnie is the On click for the Textview in a different activity.


    }

    public void AnCount(View v) {
        //increase the count
        counter++;
        showValue.setText(Integer.toString(counter));

    }

    public void ButtonToGoToTheOtherActivity(View v) {

        Intent intent = new Intent(this, Screen4.class);
        intent.putExtra("valueOfCounter", counter);   //the code for sending data to the other activity.
        startActivity(intent);


    }
}

这是屏幕 2 的 XML:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    tools:context=".Screen2">


    <Button
        android:id="@+id/AnnieBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginLeft="32dp"
        android:text="@string/annie_liou"
        android:onClick="AnCount"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView5"

        />

这是我的屏幕4:

   package com.example.myapplication1;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;


public class Screen4 extends AppCompatActivity {

    private Button Button3;

int counter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_screen4);




        Button3 = (Button) findViewById(R.id.Button3);
        Button3.setOnClickListener(new View.OnClickListener() {
                                       public void onClick(View view) { openActivity4();
                                       }
                                   }


        );
        counter = getIntent().getIntExtra("valueOfCounter", 0); // 0 is default value

    }

    public void openActivity4() {
        Intent intent = new Intent(Screen4.this, MainActivity.class);
        startActivity(intent);
    }

}

这是 screen4 的 XML:

 <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/MainScreen"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".Screen4">

        <TextView
            android:id="@+id/textView5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="193dp"
            android:layout_marginLeft="193dp"
            android:layout_marginEnd="109dp"
            android:layout_marginRight="109dp"
            android:layout_marginBottom="660dp"
            android:text="This is 4th screen"
            android:textSize="32sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.664"
            app:layout_constraintStart_toStartOf="parent" />

        <Button
            android:id="@+id/Button3" // return to main screen
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="532dp"
            android:text="Return" 
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView5" />

        <TextView
            android:id="@+id/VoteCountAnnie" // textview where i want the increment to show
            android:layout_width="121dp"
            android:gravity="center"
            android:layout_height="52dp"
            android:layout_marginStart="116dp"
            android:layout_marginLeft="116dp"
            android:layout_marginTop="82dp"
            android:layout_marginEnd="174dp"
            android:layout_marginRight="174dp"
            android:text="0"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView5" />

    </androidx.constraintlayout.widget.ConstraintLayout>

这是我的主要 Activity 屏幕(不用于点击，但如果其中有问题可能会影响其他屏幕，请告诉我):

package com.example.myapplication1;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    private Button button;
    private Button button2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                openActivity2();

            }
        });

        button2 = (Button) findViewById(R.id.button2);
        button2.setOnClickListener(new View.OnClickListener() {
                                       public void onClick(View view) {
                                           openActivity3();
                                       }

                                   }
                                   );


    }

    public void openActivity2() {
        Intent intent = new Intent(this, Screen2.class);
        startActivity(intent);
    }

    public void openActivity3() {
        Intent intent = new Intent(this, Screen3.class);
        startActivity(intent);
    }
}
Here is the XML for screen 4:

Answer 1

This works same using intent .

Main Class :

package com.example.cameraone;

import android.content.Intent;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    public static String EXTRA_VOTE_KEY = "com.example.cameraone.EXTRA_VOTE_KEY";
    private Button counter,show;
    private int count  = 0;

   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(savedInstanceState != null){
            count = savedInstanceState.getInt(EXTRA_VOTE_KEY);
        }
        counter = findViewById(R.id.bt_counter);
        show = findViewById(R.id.bt_show);
        counter.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                count++;
            }
        });

        show.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                go();
            }
        });

      /* Intent intent = new Intent(this,DisplayCount.class);
       //intent.putExtras(intent);
        startActivity(intent,bundle);*/

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt(EXTRA_VOTE_KEY,count);
    }

    public void go(){
        Intent intent = new Intent(this,DisplayCount.class);
        intent.putExtra(EXTRA_VOTE_KEY,count);
        startActivity(intent);
    }
}

Activity of Main Class :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/bt_counter"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:text="PressMe"
        />
    <Button
        android:id="@+id/bt_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/bt_counter"
        android:text="Done"
        />
</RelativeLayout


Display Class :

package com.example.cameraone;

import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.Button;
import android.widget.TextView;

import org.w3c.dom.Text;

public class DisplayCount extends AppCompatActivity{

    private  TextView textView;
    private int count;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.display_count_activity);

        textView = findViewById(R.id.tv_vote_count);
        Intent intent = getIntent();
        count = intent.getIntExtra(MainActivity.EXTRA_VOTE_KEY,0);
        textView.setText(Integer.toString(count));
    }
}


Activity of display class :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content" android:layout_height="wrap_content"
    android:layout_gravity="center">

    <TextView
        android:id="@+id/tv_vote_count"
        android:layout_width="wrap_content"
        android:inputType="number"
        android:layout_height="wrap_content"
        android:textStyle="bold"
        android:maxLength="10"/>

</RelativeLayout>


Manifest : 

include following in your   manifest file :

<activity android: name =".DisplayCount"></activity>