理解getIntExtra()参数

Question

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

  // pull the turtle's ID out of the intent that the MainActivity used to load me
    Intent intent = getIntent();
    int id = intent.getIntExtra("turtle_id", R.id.leo);
    String text = "";
    if (id == R.id.leo) {
        text = TURTLE_DETAILS[0];
    } else if (id == R.id.mike) {
        text = TURTLE_DETAILS[1];
    } else if (id == R.id.don) {
        text = TURTLE_DETAILS[2];
    } else { // if (id == R.id.raph)
        text = TURTLE_DETAILS[3];
    }

我无法解决问题

int id = intent.getIntExtra("turtle_id", R.id.leo);

我看不出为什么R.id.leo被指定了？turtle_id是名字,但我不确定R.id.leo.

片段 MainActivity.java

    /*
     * Called when the Details activity finishes running and comes back to here.
     */
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

    }

    /*
     * Called when the user clicks on the large TMNT image button.
     * Loads the DetailsActivity for more information about that turtle.
     */
    public void onClickTurtleImage(View view) {
        Intent intent = new Intent(this, DetailsActivity.class);

        RadioGroup group = (RadioGroup) findViewById(R.id.turtle_group);
        int id = group.getCheckedRadioButtonId();
        intent.putExtra("turtle_id", id);
        startActivity(intent);
    }

    /*
     * This method is called when the user chooses one of the turtle radio buttons.
     * In this code we set which turtle image is visible on the screen in the ImageView.
     */
    public void pickTurtle(View view) {
        ImageButton img = (ImageButton) findViewById(R.id.turtle);
        if (view.getId() == R.id.leo) {
            img.setImageResource(R.drawable.tmntleo);
        } else if (view.getId() == R.id.mike) {
            img.setImageResource(R.drawable.tmntmike);
        } else if (view.getId() == R.id.don) {
            img.setImageResource(R.drawable.tmntdon);
        } else if (view.getId() == R.id.raph) {
            img.setImageResource(R.drawable.tmntraph);
        }
    }
}

DetailsActivity.java

/*
 * CS 193A, Winter 2015, Marty Stepp
 * This app is a continuation of our TMNT app from last week.
 * Today's version adds a second activity and launches that activity using an Intent.
 * This file represents the Java code for the second activity.
 */

package com.example.stepp.layoutfun;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class DetailsActivity extends Activity {
    /*
     * Constant array of data about each of the four turtles.
     * (This is not the most idiomatic way to store such information,
     * but we'll come back to it later.)
     */
    private static final String[] TURTLE_DETAILS = {
            ""/*Long Story but not relevant for the question*/
    };

    /*
     * Called when the activity first gets created.
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_details);

        // pull the turtle's ID out of the intent that the MainActivity used to load me
        Intent intent = getIntent();
        int id = intent.getIntExtra("turtle_id", R.id.leo);
        String text = "";
        if (id == R.id.leo) {
            text = TURTLE_DETAILS[0];
        } else if (id == R.id.mike) {
            text = TURTLE_DETAILS[1];
        } else if (id == R.id.don) {
            text = TURTLE_DETAILS[2];
        } else { // if (id == R.id.raph)
            text = TURTLE_DETAILS[3];
        }
        TextView tv = (TextView) findViewById(R.id.turtle_info);
        tv.setText(text);
    }
}

activity_main.xml

<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:paddingLeft="@dimen/activity_horizontal_margin"
    android:gravity="top|center"
    android:orientation="vertical"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <RadioGroup
        android:id="@+id/turtle_group"
        android:orientation="horizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <RadioButton
            android:id="@+id/leo"
            android:onClick="pickTurtle"
            android:text="Leo"
            android:checked="true"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <RadioButton
            android:id="@+id/mike"
            android:onClick="pickTurtle"
            android:text="Mike"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <RadioButton
            android:id="@+id/don"
            android:onClick="pickTurtle"
            android:text="Don"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <RadioButton
            android:id="@+id/raph"
            android:onClick="pickTurtle"
            android:text="Raph"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </RadioGroup>
    <ImageButton
        android:id="@+id/turtle"
        android:onClick="onClickTurtleImage"
        android:src="@drawable/tmntleo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

使用过的教程在这里.

Answer 1

该方法的文档getIntExtra如下:

从intent中检索扩展数据.

参数

name 所需项目的名称.

defaultValue 如果没有使用给定名称存储所需类型的值,则返回该值.

返回

先前使用putExtra()添加的项的值,如果未找到,则为默认值.

因此,在您的示例中,如果该键存在,id则将分配与该键关联的整数值,否则将分配整数值.通常,如果消费者在启动此消息时未能传递必要信息,则使用此方法以便提供合理的默认值.在您的特定情况下,此行为可以解释为:"如果调用者忘记告诉我在启动时选择了哪只乌龟,则假设它是Leo."turtle_idIntentR.id.leoActivityActivity