Android学习笔记之为Dialog自定义布局，并说明空指针问题

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在使用自定义布局时经常会碰见这样的问题：edit = (EditText) findViewById(R.id.edit);并不能获取到控件对象；

在后面代码中使用edit时会报错，空指针异常。意思是edit 为null。

解决方案：

LayoutInflater factory = LayoutInflater.from(MyDialogActivity.this);  final View view = factory.inflate(R.layout.dialog, null);  edit = (EditText) view.findViewById(R.id.edit);

[java] view plain copy print ?

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[java] view plain copy print ?

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MyDialogActivity.java 文件名称 MyDialogActivity.java

R.layout.dialog：自定义布局文件 dialog.xml如何为Dialog布局呢？你需要定义一个布局文件，我在例子中定义了一个：dialog.xml

final View view = factory.inflate(R.layout.dialog, null);

得到view，用setView(view);方法设置布局。

具体实现：

dialog.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/dialogLayout"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:gravity="center_horizontal"    android:orientation="vertical" >    <EditText        android:id="@+id/edit"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:gravity="top"        android:lines="4"        android:maxLines="4" /></LinearLayout>

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:gravity="center_horizontal"    android:orientation="vertical" >        <TextView        android:id="@+id/textView"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        /></LinearLayout>

MyDialogActivity.java

package xiaosi.mydialog;import android.app.Activity;import android.app.AlertDialog;import android.content.DialogInterface;import android.content.DialogInterface.OnClickListener;import android.os.Bundle;import android.view.LayoutInflater;import android.view.View;import android.widget.EditText;import android.widget.TextView;public class MyDialogActivity extends Activity{ /** Called when the activity is first created. */ private EditText edit = null;    private TextView textview = null; @Override public void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.main);  textview = (TextView)findViewById(R.id.textView);  LayoutInflater factory = LayoutInflater.from(MyDialogActivity.this);  final View view = factory.inflate(R.layout.dialog, null);  edit = (EditText) view.findViewById(R.id.edit);  AlertDialog.Builder builder = new AlertDialog.Builder(    MyDialogActivity.this);  builder.setTitle("文字效果");  builder.setIcon(R.drawable.btn_mainmenu_words_a);  builder.setMessage("请输入你要的文字:");  builder.setView(view);  builder.setPositiveButton("提交", new SubmitListener());  builder.setNegativeButton("取消", new DismissListener());  builder.show(); } private class SubmitListener implements OnClickListener {  public void onClick(DialogInterface dialog, int which)  {   System.out.println(edit.getText().toString());   textview.setText("测试结果:\n" + edit.getText().toString());   dialog.dismiss();  } }  private class DismissListener implements OnClickListener {  public void onClick(DialogInterface dialog, int which)  {   dialog.dismiss();  } }}

           

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