java - 按钮 onclick 不适用于我的第二个 fragment android

Question

我正在为计算器编写代码，分别有两个 fragment fragmenOne和fragmentTwo。 FragmentOne 是我的默认 fragment ，其中包含加法、减法和数字等基本功能。第二个 fragment fragmentTwo 包含 sin tan cos...等高级功能。我的第二个 fragment 中的按钮不起作用，也不会附加 Editbox 。但我的fragmentOne 中的按钮工作正常。如果我首先转到fragmentTwo，然后转到fragmentOne，则按钮在fragmentOne 中也不起作用。请阐明这个特定问题。下面提供了代码和图像。

MainActivity.java

package com.example.fragmentstest;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import de.congrace.exp4j.Calculable;
import de.congrace.exp4j.ExpressionBuilder;
import de.congrace.exp4j.UnknownFunctionException;
import de.congrace.exp4j.UnparsableExpressionException;

public class MainActivity extends Activity implements View.OnClickListener {
Button one, two, three, four, five, six, seven, eight, nine, zero, add,
sub, mul, div, equal, decimal, cancel, sin, cos, tan, open_bracket, close_bracket;
EditText disp;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);
    one = (Button) findViewById(R.id.one);
    two = (Button) findViewById(R.id.two);
    three = (Button) findViewById(R.id.three);
    four = (Button) findViewById(R.id.four);
    five = (Button) findViewById(R.id.five);
    six = (Button) findViewById(R.id.six);
    seven = (Button) findViewById(R.id.seven);
    eight = (Button) findViewById(R.id.eight);
    nine = (Button) findViewById(R.id.nine);
    zero = (Button) findViewById(R.id.zero);

    add = (Button) findViewById(R.id.add);
    sub = (Button) findViewById(R.id.sub);
    mul = (Button) findViewById(R.id.mul);
    div = (Button) findViewById(R.id.div);
    equal = (Button) findViewById(R.id.equal);
    decimal = (Button) findViewById(R.id.decimal);

    sin = (Button) findViewById(R.id.sin);
    cos = (Button) findViewById(R.id.cos);
    tan = (Button) findViewById(R.id.tan);
    open_bracket = (Button) findViewById(R.id.open_bracket);
    close_bracket = (Button)findViewById(R.id.close_bracket);

    disp = (EditText) findViewById(R.id.display_panel);
    cancel = (Button) findViewById(R.id.cancel); 
    try {
        one.setOnClickListener(this);
        two.setOnClickListener(this);
        three.setOnClickListener(this);
        four.setOnClickListener(this);
        five.setOnClickListener(this);
        six.setOnClickListener(this);
        seven.setOnClickListener(this);
        eight.setOnClickListener(this);
        nine.setOnClickListener(this);
        zero.setOnClickListener(this);

        add.setOnClickListener(this);
        sub.setOnClickListener(this);
        mul.setOnClickListener(this);
        div.setOnClickListener(this);
        equal.setOnClickListener(this);
        decimal.setOnClickListener(this);
        cancel.setOnClickListener(this);
        sin.setOnClickListener(this);
        cos.setOnClickListener(this);
        tan.setOnClickListener(this);
        open_bracket.setOnClickListener(this);
        close_bracket.setOnClickListener(this);
    } catch (Exception e) {
    }
}

public void selectFrag(View view) {
    Fragment fr;

    if (view == findViewById(R.id.button2)) {
        fr = new FragmentTwo();

    } else {
        fr = new FragmentOne();

    }

    FragmentManager fm = getFragmentManager();
    FragmentTransaction fragmentTransaction = fm.beginTransaction();
    fragmentTransaction.replace(R.id.fragment_place, fr);
    fragmentTransaction.commit();

}

@Override
public void onClick(View v) {
    Editable str = disp.getText();
    switch (v.getId()) {
    case R.id.zero:
        str = str.append(zero.getText());
        disp.setText(str);
        break;
    case R.id.one:
        str = str.append(one.getText());
        disp.setText(str);
        break;
    case R.id.two:
        str = str.append(two.getText());
        disp.setText(str);
        break;
    case R.id.three:
        str = str.append(three.getText());
        disp.setText(str);
        break;
    case R.id.four:
        str = str.append(four.getText());
        disp.setText(str);
        break;
    case R.id.five:
        str = str.append(five.getText());
        disp.setText(str);
        break;
    case R.id.six:
        str = str.append(six.getText());
        disp.setText(str);
        break;
    case R.id.seven:
        str = str.append(seven.getText());
        disp.setText(str);
        break;
    case R.id.eight:
        str = str.append(eight.getText());
        disp.setText(str);
        break;
    case R.id.nine:
        str = str.append(nine.getText());
        disp.setText(str);
        break;
    case R.id.add:
        str = str.append(add.getText());
        disp.setText(str);
        break;
    case R.id.sub:
        str = str.append(sub.getText());
        disp.setText(str);
        break;
    case R.id.mul:
        str = str.append(mul.getText());
        disp.setText(str);
        break;
    case R.id.div:
        str = str.append(div.getText());
        disp.setText(str);
        break;
    case R.id.decimal:
        str = str.append(decimal.getText());
        disp.setText(str);
        break;
    case R.id.sin:
        str = str.append(sin.getText());
        disp.setText(str);
        break;
    case R.id.cos:
        str = str.append(cos.getText());
        disp.setText(str);
        break;
    case R.id.tan:
        str = str.append(tan.getText());
        disp.setText(str);
        break;  
    case R.id.open_bracket:
        str = str.append(open_bracket.getText());
        disp.setText(str);
        break;
    case R.id.close_bracket:
        str = str.append(close_bracket.getText());
        disp.setText(str);
        break;  
    case R.id.cancel:
        disp.setText("");
        disp.setHint("Perform Operation");
        break;  
    case R.id.equal:
        String val;
        val = disp.getText().toString();
        Calculable calc = null;
        try {
            Calculable result = new ExpressionBuilder(val).build();
            disp.setText(Double.toString(result.calculate()));
            /* size_num = result.calculate(); */
        } catch (UnknownFunctionException e) {
            disp.setText("ERROR");
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnparsableExpressionException e) {
            disp.setText("ERROR");
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        break;

}

}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<EditText 
   android:id="@+id/display_panel"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:hint="@string/dispHint"/> 
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >

<Button
    android:id="@+id/button1"
    style="?android:attr/buttonBarButtonStyle"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="selectFrag"
    android:paddingRight="45dp"
    android:text="@string/basic" />

<Button
    android:id="@+id/button2"
    style="?android:attr/buttonBarButtonStyle"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="selectFrag"
    android:paddingLeft="25dp"
    android:paddingRight="25dp"
    android:text="@string/adv" />

</LinearLayout>
<fragment
    android:id="@+id/fragment_place"
    android:name="com.example.fragmentstest.FragmentOne"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

</LinearLayout>

fragment_two.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffff00"
android:orientation="vertical" >

 <Button
    android:id="@+id/sin"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/sin" />

 <Button
     android:id="@+id/cos"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignParentTop="true"
     android:layout_toRightOf="@+id/sin"
     android:text="@string/cos" />

 <Button
     android:id="@+id/tan"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignParentTop="true"
     android:layout_toRightOf="@+id/cos"
     android:text="@string/tan" />

 <Button
     android:id="@+id/log"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignBaseline="@+id/In"
     android:layout_alignBottom="@+id/In"
     android:layout_toRightOf="@+id/In"
     android:text="@string/log" />

 <Button
     android:id="@+id/not"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignBaseline="@+id/log"
     android:layout_alignBottom="@+id/log"
     android:layout_toRightOf="@+id/log"
     android:text="@string/not" />

 <Button
     android:id="@+id/close_bracket"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignBaseline="@+id/open_bracket"
     android:layout_alignBottom="@+id/open_bracket"
     android:layout_toRightOf="@+id/open_bracket"
     android:text="@string/close_bracket" />

 <Button
     android:id="@+id/open_bracket"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_alignBaseline="@+id/squareroot"
     android:layout_alignBottom="@+id/squareroot"
     android:layout_toLeftOf="@+id/not"
     android:text="@string/open_bracket" />

 <Button
     android:id="@+id/In"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_below="@+id/sin"
     android:layout_toLeftOf="@+id/cos"
     android:text="@string/In" />

 <Button
     android:id="@+id/squareroot"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_below="@+id/log"
     android:layout_toLeftOf="@+id/open_bracket"
     android:text="@string/squareroot" />

</RelativeLayout>

fragment_one.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#00ffff"
android:orientation="vertical" >

<Button
    android:id="@+id/seven"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/seven" />

<Button
    android:id="@+id/nine"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_toRightOf="@+id/eight"
    android:text="@string/nine" />

<Button
    android:id="@+id/div"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_toRightOf="@+id/nine"
    android:text="@string/div" />

<Button
    android:id="@+id/eight"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/four"
    android:layout_toRightOf="@+id/seven"
    android:text="@string/eight" />

<Button
    android:id="@+id/five"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/four"
    android:layout_alignBottom="@+id/four"
    android:layout_toRightOf="@+id/four"
    android:text="@string/five" />

<Button
    android:id="@+id/six"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/five"
    android:layout_toRightOf="@+id/five"
    android:text="@string/six" />

<Button
    android:id="@+id/mul"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/six"
    android:layout_toRightOf="@+id/six"
    android:text="@string/mul" />

<Button
    android:id="@+id/two"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/one"
    android:layout_toRightOf="@+id/one"
    android:text="@string/two" />

<Button
    android:id="@+id/three"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/six"
    android:layout_alignTop="@+id/two"
    android:text="@string/three" />

<Button
    android:id="@+id/sub"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/three"
    android:layout_toRightOf="@+id/three"
    android:text="@string/sub" />

<Button
    android:id="@+id/decimal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/one"
    android:text="@string/decimal" />

<Button
    android:id="@+id/zero"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/decimal"
    android:layout_toRightOf="@+id/decimal"
    android:text="@string/zero" />

<Button
    android:id="@+id/equal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/two"
    android:layout_toRightOf="@+id/two"
    android:text="@string/equal" />

<Button
    android:id="@+id/add"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/equal"
    android:layout_toRightOf="@+id/equal"
    android:text="@string/add" />

<Button
    android:id="@+id/one"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/five"
    android:layout_toLeftOf="@+id/five"
    android:text="@string/one" />

<Button
    android:id="@+id/four"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/seven"
    android:text="@string/four" />

<Button
    android:id="@+id/cancel"
    android:layout_width="50dp"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/add"
    android:layout_alignParentTop="true"
    android:layout_toRightOf="@+id/div"
    android:text="@string/cancel" />

</RelativeLayout>

FragmentTwo.java

package com.example.fragmentstest;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


public class FragmentTwo extends Fragment{
@Override
public View onCreateView(LayoutInflater inflater,
  ViewGroup container, Bundle savedInstanceState) {

  // Inflate the layout for this fragment

  return inflater.inflate(
          R.layout.fragment_two, container, false);
 }
}

FragmentOne.java 代码与 FragmentTwo.java 相同，只是类名是 FragmentOne 并且在 'R.layout.fragment_one' 中。

Answer 1

当您的 Activity 创建后，activity_main.xml 会膨胀，它将仅包含fragment_one.xml 中的 View 。此时fragment_two.xml 的 View 将不存在(因为Fragment 将在运行时动态添加)。这意味着 findViewById(R.id.sin) 将在 onCreate 函数中返回 null，并且现在有 View 来注册 onClickListener。这就是为什么在注册 ClickListener 时需要 try catch block (以避免 NullPointerExceptions)。

您应该在 Fragments 类中注册 onClickListeners，而不是 Activity。尝试从 Activity 类中删除 setOnClickListener 调用，并在 Activity 中执行此操作。

public class FragmentTwo extends Fragment{
@Override
   public View onCreateView(LayoutInflater inflater,
  ViewGroup container, Bundle savedInstanceState) {    
  // Inflate the layout for this fragment    
  View view = inflater.inflate(
          R.layout.fragment_two, container, false);
  Button sin =  (Button) view.findViewById(R.id.sin);
  sin.setOnClickListener(...);
  //other onItemListeners go here
  return view;
 }
}

您可以通过调用 getActivity 从 Fragment 类访问 MainActivity，并将其转换为 MainActivity

((MainActivity)getActivity())