我正在编写一个应用程序，发送一封包含多个图像作为附件的电子邮件。我点击了这个链接:Android multiple email attachments using Intent设置电子邮件 Intent 和内容。但是当我单击发送按钮时应用程序强制关闭并且似乎存在空指针异常。
这是涉及的两个类的代码(仅针对电子邮件部分):
上一个邮件.java :
public class PrevEmail extends Activity{
Context context;
TextView tv,tvEmail,tvEmailAd,tvSubject,tvContent,tvLocation;
EditText etSubject,etContent,etLocation;
String subject,content,location;
Button send;
String btnSelected;
String[] imgPath;
Bundle extras;
ArrayList<Uri> uris;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.prevemail);
intializeVar();
}
private void intializeVar() {
// Links xml to java
tv = (TextView) findViewById(R.id.tv);
tvEmail = (TextView) findViewById(R.id.tvEmail);
tvEmailAd = (TextView) findViewById(R.id.tvEmailAd);
tvSubject = (TextView) findViewById(R.id.tvSubject);
tvContent = (TextView) findViewById(R.id.tvContent);
tvLocation = (TextView) findViewById(R.id.tvLocation);
etSubject = (EditText) findViewById(R.id.Subject);
etContent = (EditText) findViewById(R.id.Content);
etLocation= (EditText) findViewById(R.id.Location);
send = (Button) findViewById(R.id.bSend);
extras = getIntent().getExtras();
if(extras!=null){
btnSelected=extras.getString("Button");
imgPath=extras.getStringArray("Path");
//Sets the E-mail field according to the value received by the Bundle.
if(btnSelected.equalsIgnoreCase("case1")){
tvEmailAd.setText("email_address");
}else if(btnSelected.equalsIgnoreCase("case2")){
tvEmailAd.setText("email_address");
}else if(btnSelected.equalsIgnoreCase("case3")){
tvEmailAd.setText("email_address");
}else if(btnSelected.equalsIgnoreCase("case4")){
tvEmailAd.setText("email_address");
}
}
send.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
convertEditTextToString();
Intent emailIntent = new Intent(android.content.Intent.ACTION_SEND_MULTIPLE);
emailIntent.setType("text/plain");
emailIntent.putExtra(android.content.Intent.EXTRA_EMAIL,"email_address");
emailIntent.putExtra(android.content.Intent.EXTRA_SUBJECT,subject);
emailIntent.putExtra(android.content.Intent.EXTRA_TEXT,content);
uris = new ArrayList<Uri>();
for(String file : imgPath) {
File fileIn = new File(file);
Uri u = Uri.fromFile(fileIn);
uris.add(u);
}
emailIntent.putParcelableArrayListExtra(Intent.EXTRA_STREAM, uris);
context.startActivity(Intent.createChooser(emailIntent, "Send mail..."));
}
});
}
private void convertEditTextToString(){
subject = etSubject.getText().toString();
content = etContent.getText().toString();
location= etLocation.getText().toString();
}
}
Android list :
<?xml version="1.0" encoding="utf-8"?>
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.name.StartScreen"
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.name.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.example.name.MAINACTIVITY" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.name.PrevEmail"
android:label="@string/app_name">
</activity>
</application>
还有 Logcat:
12-02 21:44:48.180: W/dalvikvm(29329): threadid=1: thread exiting with uncaught exception (group=0x40bc4498)
12-02 21:44:48.180: E/test(29329): Exception
12-02 21:44:48.200: E/AndroidRuntime(29329): FATAL EXCEPTION: main
12-02 21:44:48.200: E/AndroidRuntime(29329): java.lang.NullPointerException
12-02 21:44:48.200: E/AndroidRuntime(29329): at com.example.name.PrevEmail$1.onClick(PrevEmail.java:100)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.view.View.performClick(View.java:4106)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.view.View$PerformClick.run(View.java:17150)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.os.Handler.handleCallback(Handler.java:615)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.os.Handler.dispatchMessage(Handler.java:92)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.os.Looper.loop(Looper.java:137)
12-02 21:44:48.200: E/AndroidRuntime(29329): at android.app.ActivityThread.main(ActivityThread.java:4792)
12-02 21:44:48.200: E/AndroidRuntime(29329): at java.lang.reflect.Method.invokeNative(Native Method)
12-02 21:44:48.200: E/AndroidRuntime(29329): at java.lang.reflect.Method.invoke(Method.java:511)
12-02 21:44:48.200: E/AndroidRuntime(29329): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:808)
12-02 21:44:48.200: E/AndroidRuntime(29329): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:575)
12-02 21:44:48.200: E/AndroidRuntime(29329): at dalvik.system.NativeStart.main(Native Method)
最佳答案
你从不初始化
Context context;
所以当执行 context.startActivity(Intent.createChooser(emailIntent, "Send mail...")); 时，它会抛出 NPE。
Logcat 消息对于调试非常有帮助。这一行:
at com.example.name.PrevEmail$1.onClick(PrevEmail.java:100)
表示在您的 Activity 的第 100 行(准确地说是在 onClick 方法内)有些东西没有正确初始化。
尝试从 logcat 中学习，这将为您节省很多时间。
关于onClick后的java空指针异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20333137/