简单的Android应用程序崩溃

Question

I'm following the Starting Another Activity tutorial on the Android Developer website but, every time I try to run my app it crashes. I have been unable to find my error but it always crashes after I hit the submit button. I'm very new to this and have no idea what's wrong.

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<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="11"
    android:targetSdkVersion="21" />

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

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

MainActivity.java

package com.example.myfirstapp;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.content.Intent;
import android.view.View;
//import android.widget.EditText;

public class MainActivity extends ActionBarActivity {

public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";

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


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

//responds to user clicking button
public void sendMessage(View view){
    Intent intent= new Intent();
    intent.setClassName("com.example.myfirstapp", "com.example.myfirstapp.DisplayMessageActivity");
    intent.putExtra(EXTRA_MESSAGE, message);
    startActivity(intent);
}
}

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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="horizontal"
tools:context="com.example.myfirstapp.MainActivity" >

<EditText android:id="@+id/edit_message"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
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.support.v7.app.ActionBarActivity;
//import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
//import android.view.LayoutInflater;
//import android.view.Menu;
import android.view.MenuItem;
//import android.view.View;
//import android.view.ViewGroup;
import android.widget.TextView;

public class DisplayMessageActivity extends ActionBarActivity {

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

    Intent intent=getIntent();
    String message=intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

    TextView textView= new TextView(this);
    textView.setTextSize(40);
    textView.setText(message);
    setContentView(textView);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

and activity_display_message.xml

<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.myfirstapp.DisplayMessageActivity" >

<TextView android="@+id/container"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world" />

</RelativeLayout>

logcat

08-26 17:53:31.124: D/gralloc_goldfish(1278): Emulator without GPU emulation detected.
08-26 17:53:49.884: I/Choreographer(1278): Skipped 56 frames!  The application may be       doing too much work on its main thread.
08-26 17:53:53.164: D/AndroidRuntime(1278): Shutting down VM
08-26 17:53:53.164: W/dalvikvm(1278): threadid=1: thread exiting with uncaught exception (group=0xb2a36ba8)
08-26 17:53:53.194: E/AndroidRuntime(1278): FATAL EXCEPTION: main
08-26 17:53:53.194: E/AndroidRuntime(1278): Process: com.example.myfirstapp, PID: 1278
08-26 17:53:53.194: E/AndroidRuntime(1278): java.lang.IllegalStateException: Could not execute method of the activity
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.view.View$1.onClick(View.java:3823)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.view.View.performClick(View.java:4438)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.view.View$PerformClick.run(View.java:18422)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.os.Handler.handleCallback(Handler.java:733)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.os.Looper.loop(Looper.java:136)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at java.lang.reflect.Method.invokeNative(Native Method)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at java.lang.reflect.Method.invoke(Method.java:515)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at dalvik.system.NativeStart.main(Native Method)
08-26 17:53:53.194: E/AndroidRuntime(1278): Caused by: java.lang.reflect.InvocationTargetException
08-26 17:53:53.194: E/AndroidRuntime(1278):     at java.lang.reflect.Method.invokeNative(Native Method)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at java.lang.reflect.Method.invoke(Method.java:515)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.view.View$1.onClick(View.java:3818)
08-26 17:53:53.194: E/AndroidRuntime(1278):     ... 11 more
08-26 17:53:53.194: E/AndroidRuntime(1278): Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.myfirstapp/com.example.myfirstapp.DisplayMessageActivity}; have you declared this activity in your AndroidManifest.xml?
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1628)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1424)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Activity.startActivityForResult(Activity.java:3424)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Activity.startActivityForResult(Activity.java:3385)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:840)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Activity.startActivity(Activity.java:3627)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at android.app.Activity.startActivity(Activity.java:3595)
08-26 17:53:53.194: E/AndroidRuntime(1278):     at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:46)
08-26 17:53:53.194: E/AndroidRuntime(1278):     ... 14 more

Answer 1

You probably need to add the 2nd activity to your manifest. Most common mistake ;)

Yep, there's the proof:

08-26 17:53:53.194: E/AndroidRuntime(1278): Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.myfirstapp/com.example.myfirstapp.DisplayMessageActivity}; have you declared this activity in your AndroidManifest.xml?

Get rid of the fully qualified name and use .DisplayMessageActivity instead.