java - developer.android.com - 我的第一个应用程序/ Hello World

Question

我已经按照 developer.android.com 上的代码编写了代码，但我遇到了一些问题。

首先，在 MainActivity.java 文件中，它用黄线标记“消息”。

其次，我的代码没有错误，但是当我运行应用程序时，文本框显示“false”并且按钮有“false”标题。当我按下按钮时，没有任何反应。有人可以帮助我吗？

主要 Activity .java:

package com.example.myfirstapp;

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

public class MainActivity extends Activity {

    public static final String EXTRA_MESSAGE = null;
    private static final String message = null;

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

    }
        public void sendMessage(View view) {
            Intent intent = new Intent(this, DisplayMessageActivity.class);;
            intent.putExtra(EXTRA_MESSAGE, message);
            startActivity(intent);
            EditText editText = (EditText) findViewById(R.id.edit_message);
            String message = editText.getText().toString();


    }
}

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="horizontal">

    <EditText android:id="@+id/edit_message"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="@+string/edit_message" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@+string/button_send"
        android:onClick="sendMessage" />
</LinearLayout>

DisplayMessageActivity.java:

package com.example.myfirstapp;

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

public class DisplayMessageActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_display_message);

        //Get the message from the intent
        Intent intent = getIntent();
        String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

        //Create the text view
        TextView textView = new TextView(this);
        textView.setTextSize(40);
        textView.setText(message);

        //Set the text view as the activity layout
        setContentView(textView);
    }


}

MyFirstApp list :

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myfirstapp"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".DisplayMessageActivity"
            android:label="@string/title_activity_display_message" >
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="com.example.myfirstapp.MainActivity" />
        </activity>
    </application>

</manifest>

感谢您的帮助，我会非常感激的。

---

现在这是代码:

主要 Activity .java:

package com.example.myfirstapp;

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

public class MainActivity extends Activity {

    public static final String EXTRA_MESSAGE = null;

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

    }
        public void sendMessage(View view) {
            EditText editText = (EditText) findViewById(R.id.edit_message);
            Intent intent = new Intent(this, DisplayMessageActivity.class);
            intent.putExtra(EXTRA_MESSAGE, message);
            startActivity(intent);


    }
}

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="horizontal">

    <EditText android:id="@+id/edit_message"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="@string/edit_message" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_send"
        android:onClick="sendMessage" />
</LinearLayout>

Answer 1

• 在您的编码启动 Activity 中，在消息变量赋值之前，所以只有它不显示消息所以使用以下方式

      Intent intent = new Intent(this, DisplayMessageActivity.class);
      intent.putExtra(EXTRA_MESSAGE, message);
      EditText editText = (EditText) findViewById(R.id.edit_message);
      String message = editText.getText().toString();
      startActivity(intent);