将多个项目添加到列表视图，每个项目从按钮单击的另一个意图接收

Question

我正在创建一个生日提醒应用程序，该应用程序从主要活动开始，使用意图进入一个新活动，人们在那里选择生日，然后将选定的出生日期、月份和年份返回到主要活动。 然后在主活动中，我创建了一个新按钮，该按钮检索生日选择器活动发送的所有信息，并尝试在每次按下按钮时将其显示在列表活动中。

我面临的问题是，如果一旦我运行应用程序，生日就会被记录并显示在列表视图中，但是如果我添加另一个生日并尝试在列表视图中显示它，之前的记录会被删除，我只剩下目前的记录了。

我真正想知道的是如何在我的 listView 中添加项目，以便同时显示我以前的所有生日。

提供的代码文件如下： activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    android:weightSum="10"
    tools:context=".MainActivity">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="1"
        android:background="#97B252D5">

        <TextView
            android:id="@+id/editText"
            android:layout_width="213dp"
            android:layout_height="52dp"
            android:ems="10"
            android:fontFamily="sans-serif-black"
            android:text="Remindro"
            android:textAllCaps="true"
            android:textAppearance="@style/TextAppearance.AppCompat.Large"
            android:textSize="36sp"
            android:textStyle="bold|italic"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.067"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/newEntry"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="#C1E6E60F"
            android:fontFamily="sans-serif-black"
            android:onClick="addNewEntry"
            android:text="+ADD"
            android:textAppearance="@style/TextAppearance.AppCompat.Large"
            android:textSize="30sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.88"
            app:layout_constraintStart_toEndOf="@+id/editText"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.48" />
    </androidx.constraintlayout.widget.ConstraintLayout>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:layout_weight="9"
        android:background="#A071D4ED">


        <ListView
            android:id="@+id/list"
            android:layout_width="410dp"
            android:layout_height="596dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/viewRecord"
            app:layout_constraintVertical_bias="0.0" />

        <Button
            android:id="@+id/viewRecord"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginTop="16dp"
            android:background="#9650EC31"
            android:onClick="viewRecord"
            android:text="View Record"
            android:textAppearance="@style/TextAppearance.AppCompat.Large"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/_dynamic"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.0" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</LinearLayout>

代码文件：MainActivity.java

package com.example.remindro;

import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import androidx.appcompat.app.AppCompatActivity;

import java.util.ArrayList;
import java.util.Calendar;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "";

    ArrayList<String> listItems = new ArrayList<String>();

    ArrayAdapter<String> adapter;

    Calendar calendar = Calendar.getInstance();
    int thisYear = calendar.get(Calendar.YEAR);
    int thisMonth = calendar.get(Calendar.MONTH) + 1;
    int thisDay = calendar.get(Calendar.DAY_OF_MONTH);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        adapter=new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1,
                listItems);
        ListView records = (ListView) findViewById(R.id.list);
        records.setAdapter(adapter);
    }

    public void addNewEntry(View v)
    {
        Intent adding = new Intent();
        adding.setClass(this,addinglist.class);
        startActivity(adding);
        finish();

    }
    public void viewRecord(View v)
    {
        Intent receiver = getIntent();
        int day = receiver.getIntExtra("day",0);
        int month = receiver.getIntExtra("month",0);
        int year = receiver.getIntExtra("year",0);
        String name = receiver.getStringExtra("nameofperson");
        String choice = receiver.getStringExtra("radio");
        String mss = name + " has his " + choice + " on " + day + "/" + month + "/" + year;
        //Toast.makeText(getApplicationContext(),mss,Toast.LENGTH_LONG).show();

        int age = thisYear - year;
        calendar.set(thisYear,thisMonth,thisDay);
        Calendar calendar1 = Calendar.getInstance();
        calendar1.set(thisYear,month,day);

        long milliseconds1 = calendar.getTimeInMillis();
        long milliseconds2 = calendar1.getTimeInMillis();
        long diff = milliseconds2 - milliseconds1;
        int noOfDays = (int) (diff / (24 * 60 * 60 * 1000));
        String msg2 = "Turning " + age + " in " + noOfDays + "days!!";
//        Toast.makeText(getApplicationContext(),msg2,Toast.LENGTH_LONG).show();


        String finalMsg = mss + " " + msg2;
        listItems.add(finalMsg);
        adapter.notifyDataSetChanged();
    }
}

activity_addinglist.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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#8AEC9F18"
    tools:context=".addinglist">

    <NumberPicker
        android:id="@+id/day"
        android:layout_width="97dp"
        android:layout_height="131dp"
        android:background="#B5EA1241"
        android:scaleX="1.3"
        android:scaleY="1.3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.298">

    </NumberPicker>

    <NumberPicker
        android:id="@+id/month"
        android:layout_width="97dp"
        android:layout_height="131dp"
        android:layout_marginStart="60dp"
        android:layout_marginLeft="60dp"
        android:background="#B5EA1241"
        android:scaleX="1.3"
        android:scaleY="1.3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@+id/day"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.298">

    </NumberPicker>

    <NumberPicker
        android:id="@+id/year"
        android:layout_width="97dp"
        android:layout_height="131dp"
        android:layout_marginStart="56dp"
        android:layout_marginLeft="56dp"
        android:background="#B5EA1241"
        android:scaleX="1.3"
        android:scaleY="1.3"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@+id/month"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.298">

    </NumberPicker>

    <Button
        android:id="@+id/submit"
        android:layout_width="121dp"
        android:layout_height="59dp"
        android:layout_marginBottom="156dp"
        android:background="#9A7CEF46"
        android:onClick="addingEvent"
        android:text="ADD Event"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <RadioGroup
        android:id="@+id/typer"
        android:layout_width="384dp"
        android:layout_height="88dp"
        app:layout_constraintBottom_toTopOf="@+id/submit"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.407"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/month"
        app:layout_constraintVertical_bias="0.666">

        <RadioButton
            android:id="@+id/birthday"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Birthday"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />

        <RadioButton
            android:id="@+id/anniversary"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Anniversary"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />
    </RadioGroup>

    <EditText
        android:id="@+id/name"
        android:layout_width="413dp"
        android:layout_height="53dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:hint="Enter the Name of the Person"
        app:layout_constraintBottom_toTopOf="@+id/month"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.045"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.475" />

    <EditText
        android:id="@+id/resultshower"
        android:layout_width="412dp"
        android:layout_height="95dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.045"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/submit"
        app:layout_constraintVertical_bias="0.518" />

</androidx.constraintlayout.widget.ConstraintLayout>

并添加list.java

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.CompoundButton;
import android.widget.EditText;
import android.widget.NumberPicker;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Switch;

public class addinglist extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_addinglist);
        NumberPicker day = (NumberPicker) findViewById(R.id.day);
        NumberPicker month = (NumberPicker) findViewById((R.id.month));
        NumberPicker year = (NumberPicker) findViewById(R.id.year);
        day.setMinValue(1);
        day.setMaxValue(31);
        month.setMinValue(1);
        month.setMaxValue(12);
        year.setMinValue(1950);
        year.setMaxValue(2020);
    }

    public void addingEvent(View v)
    {
        String name;
        EditText nameEntered = (EditText) findViewById(R.id.name);
        name = nameEntered.getText().toString();
        NumberPicker day = (NumberPicker) findViewById(R.id.day);
        NumberPicker month = (NumberPicker) findViewById((R.id.month));
        NumberPicker year = (NumberPicker) findViewById(R.id.year);
        int day1 = day.getValue();
        int month1 = month.getValue();
        int year1 = year.getValue();
        RadioGroup typer = (RadioGroup) findViewById(R.id.typer);
        int selectedId = typer.getCheckedRadioButtonId();
        RadioButton checked = (RadioButton) findViewById(selectedId);
        String typee = checked.getText().toString();
        EditText resultbox = (EditText) findViewById(R.id.resultshower);
        String Finalmsg = name + " has his " + typee + " on " + day1 + "/" + month1 + "/" + year1;
        resultbox.setText(Finalmsg);
        Intent newintent = new Intent();
        newintent.putExtra("nameofperson",name);
        newintent.putExtra("day",day1);
        newintent.putExtra("month",month1);
        newintent.putExtra("year",year1);
        newintent.putExtra("radio",typee);
        newintent.setClass(this,MainActivity.class);
        startActivity(newintent);
    }
}

提前感谢您抽出时间来解决此问题。

Answer 1

要从活动中获取结果，您应该使用 startActivityForResult() 和 onActivityResult() API，而不是 startActivity()。

您可以从 tutorialspoint 给出的这个简单示例中学习它：https://www.tutorialspoint.com/how-to-manage-startactivityforresult-on-android

但最新的 Android 开发者文档建议我们为此使用新的Activity Result API。

要学习，可以参考谷歌的文档：https://developer.android.com/training/basics/intents/result

Wajahat Karim 写的这篇文章：https://wajahatkarim.com/2020/05/activity-results-api-onactivityresult/

我正在尝试使用这个新的 Activity Result API 为您提供答案。

首先，您必须添加 AndroidX Activity 和 Fragment 库作为依赖项。

app/build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"

    defaultConfig {
        applicationId "com.lakindu.birthdayreminder"
        minSdkVersion 14
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

    // Reference 1 : https://developer.android.com/training/basics/intents/result
    // Reference 2 : https://wajahatkarim.com/2020/05/activity-results-api-onactivityresult/
    implementation 'androidx.activity:activity:1.2.0-alpha04'
    implementation 'androidx.fragment:fragment:1.3.0-alpha04'
}

我将把一个 Parcelable 对象从添加列表活动发送到 MainActivity 作为结果。

这是 Parcelable Event 类的实现。

Event.java

import android.os.Parcel;
import android.os.Parcelable;

public class Event implements Parcelable {

    // Name of the person
    private String nameOfPerson;

    // Day of month
    // byte (8 bit) as the type, because day can only have a value from 1 to 31
    private byte day;

    // Month of year
    // byte (8 bit) as the type, because month can only have a value from 1 to 12
    private byte month;

    // Year
    // Short (16 bit) as the type, because year can only have a realistic A.D. year
    private short year;

    // Type of event
    private String eventType;

    // Constructor (auto-generated using Android Studio)
    public Event(String nameOfPerson, byte day, byte month, short year, String eventType) {
        this.nameOfPerson = nameOfPerson;
        this.day = day;
        this.month = month;
        this.year = year;
        this.eventType = eventType;
    }

    // Getters for each private member field (auto-generated using Android Studio)

    public String getNameOfPerson() {
        return nameOfPerson;
    }

    public byte getDay() {
        return day;
    }

    public byte getMonth() {
        return month;
    }

    public short getYear() {
        return year;
    }

    public String getEventType() {
        return eventType;
    }

    // Parcelable implementation (auto-generated using Android Studio)

    protected Event(Parcel in) {
        nameOfPerson = in.readString();
        day = in.readByte();
        month = in.readByte();
        year = (short) in.readInt();
        eventType = in.readString();
    }

    public static final Creator<Event> CREATOR = new Creator<Event>() {
        @Override
        public Event createFromParcel(Parcel in) {
            return new Event(in);
        }

        @Override
        public Event[] newArray(int size) {
            return new Event[size];
        }
    };

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(nameOfPerson);
        dest.writeByte(day);
        dest.writeByte(month);
        dest.writeInt((int) year);
        dest.writeString(eventType);
    }
}

然后我们必须创建一个类来封装来自 MainActivity 的添加列表活动的输入（在此示例中没有），以及从添加列表活动返回的输出到 MainActivity（Event Parcelable 对象）。

这个类是一个ActivityResultContract，它就像我们给Android系统的一个契约，用来打开一个特定的Activity，并为我们得到一个结果。

import android.app.Activity;
import android.content.Context;
import android.content.Intent;

import androidx.activity.result.contract.ActivityResultContract;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

public class GetEvent extends ActivityResultContract<Void, Event> {

    @NonNull
    @Override
    public Intent createIntent(@NonNull Context context, Void input) {

        // Create Intent that should be used to start addinglist activity for result
        Intent intent = new Intent(context, addinglist.class);

        // If you need to send any inputs to addinglist activity,
        // you can put them in intent as extras.
        // Eg: intent.putExtra("input", input)
        // But for now we don't have to send any inputs to addinglist activity.

        return intent;
    }

    @Override
    public Event parseResult(int resultCode, @Nullable Intent intent) {

        // Action is cancelled? Return null
        if(Activity.RESULT_OK != resultCode) return null;

        // No intent to get output? Return null
        if(null == intent) return null;

        // Successfully got result from addinglist activity
        return intent.getExtras().getParcelable("output");
    }
}

这是我们从 MainActivity 启动添加列表活动并获取结果的方式。

MainActivity.java

import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import androidx.activity.ComponentActivity;
import androidx.activity.result.ActivityResultCallback;
import androidx.activity.result.ActivityResultLauncher;

import java.util.ArrayList;
import java.util.Calendar;

public class MainActivity extends ComponentActivity {

    private static final String TAG = "";

    ArrayList<String> listItems = new ArrayList<String>();

    ArrayAdapter<String> adapter;

    Calendar calendar = Calendar.getInstance();
    int thisYear = calendar.get(Calendar.YEAR);
    int thisMonth = calendar.get(Calendar.MONTH) + 1;
    int thisDay = calendar.get(Calendar.DAY_OF_MONTH);

    // Holds the latest event received from addinglist activity
    private Event mLatestEvent = null;

    // Register a callback to be called on an event received from addinglist activity
    private ActivityResultLauncher<Void> mGetEvent = registerForActivityResult(
            // Instance that encapsulates input and output when starting addinglist activity for result
            new GetEvent(),

            // Callback to be called when event is received
            new ActivityResultCallback<Event>() {
                @Override
                public void onActivityResult(Event result) {
                    // Save as latest event received
                    mLatestEvent = result;
                }
            }
    );

    private static final Void NO_INPUT = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        adapter=new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1,
                listItems);
        ListView records = (ListView) findViewById(R.id.list);
        records.setAdapter(adapter);
    }

    public void addNewEntry(View v)
    {
        // Launch addinglist activity to get an event
        mGetEvent.launch(NO_INPUT);
    }
    public void viewRecord(View v)
    {
        // No latest event? Then nothing to add to list, just return.
        if(null == mLatestEvent) return;

        // Prepare string that is being added to the list.
        // Using a StringBuilder as there are multiple number of immutable strings to be appended.
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append(mLatestEvent.getNameOfPerson())
                .append(" has his ")
                .append(mLatestEvent.getEventType())
                .append(" on ")
                .append(mLatestEvent.getDay())
                .append("/")
                .append(mLatestEvent.getMonth())
                .append("/")
                .append(mLatestEvent.getYear());

        String mss = stringBuilder.toString();
        //Toast.makeText(getApplicationContext(),mss,Toast.LENGTH_LONG).show();

        int age = thisYear - mLatestEvent.getYear();
        calendar.set(thisYear,thisMonth,thisDay);
        Calendar calendar1 = Calendar.getInstance();
        calendar1.set(thisYear, mLatestEvent.getMonth(), mLatestEvent.getDay());

        long milliseconds1 = calendar.getTimeInMillis();
        long milliseconds2 = calendar1.getTimeInMillis();
        long diff = milliseconds2 - milliseconds1;
        int noOfDays = (int) (diff / (24 * 60 * 60 * 1000));
        String msg2 = "Turning " + age + " in " + noOfDays + "days!!";
//        Toast.makeText(getApplicationContext(),msg2,Toast.LENGTH_LONG).show();


        String finalMsg = mss + " " + msg2;
        listItems.add(finalMsg);
        adapter.notifyDataSetChanged();
    }
}

请注意，MainActivity 现在是ComponentActivity。不是 AppCompatActivity。

这里是如何将添加列表活动的结果发送到 MainActivity。

addinglist.java

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.NumberPicker;
import android.widget.RadioButton;
import android.widget.RadioGroup;

import androidx.appcompat.app.AppCompatActivity;

public class addinglist extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_addinglist);
        NumberPicker day = (NumberPicker) findViewById(R.id.day);
        NumberPicker month = (NumberPicker) findViewById((R.id.month));
        NumberPicker year = (NumberPicker) findViewById(R.id.year);
        day.setMinValue(1);
        day.setMaxValue(31);
        month.setMinValue(1);
        month.setMaxValue(12);
        year.setMinValue(1950);
        year.setMaxValue(2020);
    }

    public void addingEvent(View v)
    {
        String name;
        EditText nameEntered = (EditText) findViewById(R.id.name);
        name = nameEntered.getText().toString();
        NumberPicker day = (NumberPicker) findViewById(R.id.day);
        NumberPicker month = (NumberPicker) findViewById((R.id.month));
        NumberPicker year = (NumberPicker) findViewById(R.id.year);
        byte day1 = (byte) day.getValue();
        byte month1 = (byte) month.getValue();
        short year1 = (short) year.getValue();
        RadioGroup typer = (RadioGroup) findViewById(R.id.typer);
        int selectedId = typer.getCheckedRadioButtonId();
        RadioButton checked = (RadioButton) findViewById(selectedId);
        String typee = checked.getText().toString();
        EditText resultbox = (EditText) findViewById(R.id.resultshower);
        String Finalmsg = name + " has his " + typee + " on " + day1 + "/" + month1 + "/" + year1;
        resultbox.setText(Finalmsg);

        // Prepare the result to output
        Intent newintent = new Intent();
        newintent.putExtra(
                "output",
                new Event(name, day1, month1, year1, typee)
        );

        // Set the result
        setResult(Activity.RESULT_OK, newintent);

        // Finish the addinglist activity.
        // Then result will be sent to the MainActivity.
        finish();
    }
}

这是正在运行的应用程序。