Java Android我的第一个应用程序教程Android:onClick问题

我目前正试图让谷歌创建的安卓基本应用程序教程（我的第一个应用程序教程）正常运行，但我遇到了一些问题。目前，Eclipse中没有显示应用程序如何生成的错误，但当我运行应用程序并单击“发送”按钮时，应用程序崩溃，不幸的是，我的第一个应用程序已停止

在日志cat中查找它声明的错误

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，但它是函数占位符片段中的嵌套类。最初我认为这是一个索引错误，所以我尝试像调用嵌套类android:onClick=PlaceholderFragment.sendMessage一样调用sendMessage，但没有成功。我已经包含了fragment_main和MainActivity类以及我的完整logcat错误。谢谢你的帮助

主要活动：

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);
        }

    }

}

主要片段：

<?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>

---

看起来您的问题是sendMessage函数应该包含在MainActivity中，而不是嵌套在片段中

调试行：

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

---

显示应用程序正在MainActivity类中查找此方法。

将sendMessageView视图方法放置在MainActivity类中，而不是Placeholder Fragment类中。

从xml处理clicklistener并不总是一个好主意。在按钮的片段中设置clicklistener，并从clicklistener的onClick方法调用sendMessage方法

首先设置按钮的ID示例：sendButton

那么

或者在片段中实现View.OnClickListener，然后使用如下case语句：

@Override
public void onClick(View view) {
    switch (view.getId()) {
        case R.id.sendButton:
            sendMessage();
            break;
        default:
            Log.i(TAG, "Unknown: " + view.getId());
            break;
    }
}

---

以编程方式执行此操作：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        Button b = (Button) rootView.findViewById(R.id.my_button);
        b.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // handle click here
            }
        });
        return rootView;
} 

并将其插入主活动布局中的按钮部分：

---

android:id=@+id/my_按钮

按钮onClick属性搜索活动中的相应方法。但是您在片段中定义了该方法，这就是为什么会出现异常 方法找不到异常

Android推荐的处理片段内部onClick for按钮的方法是 首先将id分配给按钮

<?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:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
     />
   </LinearLayout>

---

当我执行此操作时，会出现此错误，类型MainActivity的方法getActivity未定义我猜getActivity是包含在Placeholder Fragment类的Androids支持库中的函数。尝试了此操作，但是我得到一个错误，阻止我导入OnClickListener导入android.support.v7.internal.widget.AdapterViewICS.OnItemClickListener//错误：类型android.support.v7.internal.widget.AdapterViewICS不可见

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        Button b = (Button) rootView.findViewById(R.id.my_button);
        b.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // handle click here
            }
        });
        return rootView;
} 

<?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:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
     />
   </LinearLayout>

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

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
     Button b = (Button) rootView.findViewById(R.id.button1);
    b.setOnClickListener(this);
        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);
    }

    public void onClick(View view)
    {
       sendMessage(view);
    }
}