java - Android 我的第一个应用程序教程 android :onClick issues

Question

我目前正在尝试让 Android 的基本“我的第一个应用程序”教程(由 google 创建)正常工作，但遇到了一些问题。目前，该应用程序的制作方式在 Eclipse 中没有显示任何错误，但是当我运行该应用程序并单击“发送”按钮时，该应用程序崩溃，显示 不幸的是，我的第一个应用程序已停止。

在日志猫中查找它指出的错误

java.lang.IllegalStateException: Could not find a method sendMessage(View) 
in the activity class com.example.myfirstapp.MainActivity for onClick handler 
on view class android.widget.Button. 

sendMessage 确实存在于 MainActivity 类中，但它是函数 PlaceholderFragment 内的嵌套类。最初我认为这是一个索引错误，所以我尝试像嵌套类 android:onClick="PlaceholderFragment.sendMessage" 一样调用 sendMessage 但没有成功。我已包含 fragment_main 和 MainActivity 类以及完整的 logcat 错误。感谢您的帮助。

主要 Activity :

package com.example.myfirstapp;

import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
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);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }


    @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);
    }

    /**
    * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }
        /** Called when the user clicks the Send button */
        public void sendMessage(View view) {
            Intent intent = new Intent(getActivity(), DisplayMessageActivity.class);
            EditText editText = (EditText)getActivity(). findViewById(R.id.edit_message);
            String message = editText.getText().toString();
            intent.putExtra(EXTRA_MESSAGE, message);
            startActivity(intent);
        }

    }

}

fragment 主要:

<?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>

日志猫:

04-25 12:04:07.220: D/(1274): HostConnection::get() New Host Connection established 0xb8e4f238, tid 1274
04-25 12:04:07.330: W/EGL_emulation(1274): eglSurfaceAttrib not implemented
04-25 12:04:07.340: D/OpenGLRenderer(1274): Enabling debug mode 0
04-25 12:04:10.620: D/AndroidRuntime(1274): Shutting down VM
04-25 12:04:10.620: W/dalvikvm(1274): threadid=1: thread exiting with uncaught exception (group=0xb2a6bba8)
04-25 12:04:10.750: E/AndroidRuntime(1274): FATAL EXCEPTION: main
04-25 12:04:10.750: E/AndroidRuntime(1274): Process: com.example.myfirstapp, PID: 1274
04-25 12:04:10.750: E/AndroidRuntime(1274): java.lang.IllegalStateException: Could not find a method sendMessage(View) in the activity class com.example.myfirstapp.MainActivity for onClick handler on view class android.widget.Button
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.view.View$1.onClick(View.java:3810)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.view.View.performClick(View.java:4438)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at     android.view.View$PerformClick.run(View.java:18422)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.os.Handler.handleCallback(Handler.java:733)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.os.Handler.dispatchMessage(Handler.java:95)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.os.Looper.loop(Looper.java:136)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.app.ActivityThread.main(ActivityThread.java:5017)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at java.lang.reflect.Method.invokeNative(Native Method)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at java.lang.reflect.Method.invoke(Method.java:515)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at dalvik.system.NativeStart.main(Native Method)
04-25 12:04:10.750: E/AndroidRuntime(1274): Caused by: java.lang.NoSuchMethodException: sendMessage [class android.view.View]
04-25 12:04:10.750: E/AndroidRuntime(1274):     at java.lang.Class.getConstructorOrMethod(Class.java:472)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at java.lang.Class.getMethod(Class.java:857)
04-25 12:04:10.750: E/AndroidRuntime(1274):     at android.view.View$1.onClick(View.java:3803)
04-25 12:04:10.750: E/AndroidRuntime(1274):     ... 11 more
04-25 12:04:12.720: I/Process(1274): Sending signal. PID: 1274 SIG: 9

Answer 1

看来您的问题是 sendMessage 函数应该包含在您的 MainActivity 中，而不是嵌套在您的 fragment 中。

调试线:

java.lang.IllegalStateException: Could not find a method sendMessage(View) in the activity class com.example.myfirstapp.MainActivity for onClick handler on view class android.widget.Button

表明应用程序正在您的 MainActivity 类中查找此方法。