java - 了解 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];
    }

我不会画线

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

我不明白为什么要指定 R.id.leo？ turtle_id 是名称，但我不确定 R.id.leo 的意义。

MainActivity.java 的 fragment

    /*
     * 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>

使用的教程是here .

Answer 1

documentation for the getIntExtra method如下:

Retrieve extended data from the intent.

Parameters

name The name of the desired item.

defaultValue the value to be returned if no value of the desired type is stored with the given name.

Returns

the value of an item that previously added with putExtra() or the default value if none was found.

因此，在您的示例中，如果 Intent 中存在该键，则 id 将被分配与键 turtle_id 关联的整数值，并且如果不是，将被分配整数值 R.id.leo。通常，如果消费者在启动此 Activity 时未能传递必要的信息，则使用它来提供合理的默认值。在您的特定情况下，此行为可以解释为:“如果调用者在启动此 Activity 时忘记告诉我选择了哪只乌龟，则假设它是 Leo。”