使用saveInstanceState保存数据

Question

MainActivity.java

 package com.jamesvuong.footballscorekeeper;

    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    final int TOUCHDOWN_POINTS = 6;
    final int FIELD_GOAL_POINTS = 3;
    final int EXTRA_POINT_1_POINT = 1;
    final int EXTRA_POINT_2_POINTS = 2;
    final int SAFETY_POINTS = 2;
    String score_a , score_b;
    String TEXT_A , TEXT_B;
    int team_a_score;
    int team_b_score;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); // Always call the superclass first


        // Check whether we're recreating a previously destroyed instance
        if (savedInstanceState != null) {
            // Restore value of members from saved state
            team_a_score = savedInstanceState.getInt(TEXT_A);
            team_b_score = savedInstanceState.getInt(TEXT_B);
        }
        else {
            // Probably initialize members with default values for a new instance
            team_a_score = 0;
            team_b_score = 0;
        }
        setContentView(R.layout.activity_main);
        displayTeamAScore(team_a_score);
        displayTeamBScore(team_b_score);

    }



    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        // Save the user's current game state
        savedInstanceState.putInt(TEXT_A,team_a_score);
        savedInstanceState.putInt(TEXT_B, team_b_score);


        // Always call the superclass so it can save the view hierarchy state
        super.onSaveInstanceState(savedInstanceState);
    }
    public void onRestoreInstanceState(Bundle savedInstanceState) {
        // Always call the superclass so it can restore the view hierarchy
        super.onRestoreInstanceState(savedInstanceState);


        // Restore state members from saved instance
        team_a_score = savedInstanceState.getInt(TEXT_A);
        team_b_score = savedInstanceState.getInt(TEXT_B);
    }


    /**
     * Update Scores
     */
    public void resetScores(View v) {
        team_a_score = 0;
        team_b_score = 0;
        displayTeamAScore(team_a_score);
        displayTeamBScore(team_b_score);
    }

    public void updateTeamScore(View v) {
        switch(v.getId()) {
            case R.id.team_a_touchdown:
                team_a_score += TOUCHDOWN_POINTS;
                break;
            case R.id.team_a_field_goal:
                team_a_score += FIELD_GOAL_POINTS;
                break;
            case R.id.team_a_extra_point_1:
                team_a_score += EXTRA_POINT_1_POINT;
                break;
            case R.id.team_a_extra_point_2:
                team_a_score += EXTRA_POINT_2_POINTS;
                break;
            case R.id.team_a_safety:
                team_a_score += SAFETY_POINTS;
                break;

            case R.id.team_b_touchdown:
                team_b_score += TOUCHDOWN_POINTS;
                break;
            case R.id.team_b_field_goal:
                team_b_score += FIELD_GOAL_POINTS;
                break;
            case R.id.team_b_extra_point_1:
                team_b_score += EXTRA_POINT_1_POINT;
                break;
            case R.id.team_b_extra_point_2:
                team_b_score += EXTRA_POINT_2_POINTS;
                break;
            case R.id.team_b_safety:
                team_b_score += SAFETY_POINTS;
                break;

            default:
                break;
        }

        displayTeamAScore(team_a_score);
        displayTeamBScore(team_b_score);
    }

    /**
     * Display Scores
     */
    public void displayTeamAScore(int score) {
        TextView scoreView = (TextView) findViewById(R.id.team_a_score);
        scoreView.setText(String.valueOf(score));
    }

    public void displayTeamBScore(int score) {
        TextView scoreView = (TextView) findViewById(R.id.team_b_score);
        scoreView.setText(String.valueOf(score));
    }

}

Activity_main.XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="10dp"
    tools:context="com.jamesvuong.footballscorekeeper.MainActivity">


    <LinearLayout
        android:id="@+id/score_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="2"
        android:layout_marginBottom="10dp"
        android:orientation="horizontal">

        <LinearLayout
            android:id="@+id/team_a_score_container"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="6"
            android:orientation="vertical">

            <TextView
                android:id="@+id/team_a_label"
                android:text="Team A"
                style="@style/TeamLabelStyle"/>

            <TextView
                android:id="@+id/team_a_score"
                android:text="0"
                android:saveEnabled="true"
                style="@style/ScoreTextStyle"/>

        </LinearLayout>

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1">
            <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text="-"
                android:gravity="center"
                android:textStyle="bold"
                android:textSize="30sp"/>
        </LinearLayout>

        <LinearLayout
            android:id="@+id/team_b_score_container"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="6"
            android:orientation="vertical">

            <TextView
                android:id="@+id/team_b_label"
                android:text="Team B"
                style="@style/TeamLabelStyle"/>

            <TextView
                android:id="@+id/team_b_score"
                android:text="0"
                android:saveEnabled="true"
                style="@style/ScoreTextStyle"/>

        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@android:color/darker_gray"
        android:layout_marginBottom="10dp">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </LinearLayout>

    <LinearLayout
        android:id="@+id/scoring_buttons_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="4"
        android:layout_gravity="center"
        android:orientation="vertical">

        <LinearLayout
            android:id="@+id/touchdown_container"
            style="@style/ScoreTypeButtonContainerStyle">

            <Button
                android:id="@+id/team_a_touchdown"
                style="@style/ScoreButtonStyle"
                android:text="+6"
                android:onClick="updateTeamScore"/>

            <TextView
                android:text="Touchdown"
                style="@style/ScoreTypeLabelStyle"/>

            <Button
                android:id="@+id/team_b_touchdown"
                style="@style/ScoreButtonStyle"
                android:text="+6"
                android:onClick="updateTeamScore"/>

        </LinearLayout>

        <LinearLayout
            android:id="@+id/field_goal_container"
            style="@style/ScoreTypeButtonContainerStyle">

            <Button
                android:id="@+id/team_a_field_goal"
                style="@style/ScoreButtonStyle"
                android:text="+3"
                android:onClick="updateTeamScore"/>

            <TextView
                android:text="Field Goal"
                style="@style/ScoreTypeLabelStyle"/>

            <Button
                android:id="@+id/team_b_field_goal"
                style="@style/ScoreButtonStyle"
                android:text="+3"
                android:onClick="updateTeamScore"/>

        </LinearLayout>

        <LinearLayout
            android:id="@+id/extra_point_container"
            style="@style/ScoreTypeButtonContainerStyle">

            <Button
                android:id="@+id/team_a_extra_point_1"
                style="@style/ScoreButtonStyle"
                android:text="+1"
                android:onClick="updateTeamScore"/>

            <Button
                android:id="@+id/team_a_extra_point_2"
                style="@style/ScoreButtonStyle"
                android:text="+2"
                android:onClick="updateTeamScore"/>

            <TextView
                style="@style/ScoreTypeLabelStyle"
                android:text="Extra Point" />

            <Button
                android:id="@+id/team_b_extra_point_1"
                style="@style/ScoreButtonStyle"
                android:text="+1"
                android:onClick="updateTeamScore"/>

            <Button
                android:id="@+id/team_b_extra_point_2"
                style="@style/ScoreButtonStyle"
                android:text="+2"
                android:onClick="updateTeamScore"/>

        </LinearLayout>

        <LinearLayout
            android:id="@+id/safety_container"
            style="@style/ScoreTypeButtonContainerStyle">

            <Button
                android:id="@+id/team_a_safety"
                style="@style/ScoreButtonStyle"
                android:text="+2"
                android:onClick="updateTeamScore"/>

            <TextView
                style="@style/ScoreTypeLabelStyle"
                android:text="Safety"/>

            <Button
                android:id="@+id/team_b_safety"
                style="@style/ScoreButtonStyle"
                android:text="+2"
                android:onClick="updateTeamScore"/>

        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@android:color/darker_gray"
        android:layout_marginBottom="10dp">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </LinearLayout>


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="vertical">

        <Button
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#333333"
            android:onClick="resetScores"
            android:text="Reset"
            android:textColor="#FFFFFF" />

    </LinearLayout>
</LinearLayout>

I want to save some values, like score of both the team, so that even after the app is killed(not running anymore in background) the scores are saved and can be retained back when the user again opens the app.I have tried using 'savedInstanceState' but its not working. Please help. I am a beginner in android development.

Answer 1

savedInstanceState is used to save the current state of the app during screen rotations, not to save data permanently. SharedPreferences is what you are looking for. Here is an example :

SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);

// save
sharedPreferences.edit()
        .putString("key1", "value")
        .putInt("key2", 10)
        .apply();

// retrieve
String stringValue = sharedPreferences.getString("key1", null);
int intValue = sharedPreferences.getInt("key2", -1);

// null and -1 are default values if not found

Answer 2

如果您的应用尚未被终止，那么您可以使用saveInstanceState / Application类存储值，否则您必须使用Shared-preference或Sqlite / Other ORM。