我目前正在尝试创建一个App，它允许用户从图库中拍摄图像并将其上传到服务器。但我仍然坚持选择一个图像。 我完全按照教程，但在启动活动时，我得到了一个NullPointer。
你们看到有什么错误吗？
提前致谢！
继承代码;
package de.arvidg.exampleactionbartabs;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
public class UploadPicture extends Activity {
private static int RESULT_LOAD_IMAGE = 1;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button buttonLoadImage = (Button) findViewById(R.id.choosepic2);
buttonLoadImage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent i = new Intent(
Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(i, RESULT_LOAD_IMAGE);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && null != data) {
Uri selectedImage = data.getData();
String[] filePathColumn = { MediaStore.Images.Media.DATA };
Cursor cursor = getContentResolver().query(selectedImage,
filePathColumn, null, null, null);
cursor.moveToFirst();
int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
String picturePath = cursor.getString(columnIndex);
cursor.close();
ImageView imageView = (ImageView) findViewById(R.id.chosenPicView);
imageView.setImageBitmap(BitmapFactory.decodeFile(picturePath));
}
}
}
logcat的：
03-17 10:56:35.470: W/dalvikvm(12169): threadid=1: thread exiting with uncaught exception (group=0x41e64300)
03-17 10:56:35.480: E/AndroidRuntime(12169): FATAL EXCEPTION: main
03-17 10:56:35.480: E/AndroidRuntime(12169): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.arvidg.exampleactionbartabs/de.arvidg.exampleactionbartabs.UploadPicture}: java.lang.NullPointerException
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2190)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2215)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread.access$600(ActivityThread.java:145)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1211)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.os.Handler.dispatchMessage(Handler.java:99)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.os.Looper.loop(Looper.java:137)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread.main(ActivityThread.java:4978)
03-17 10:56:35.480: E/AndroidRuntime(12169): at java.lang.reflect.Method.invokeNative(Native Method)
03-17 10:56:35.480: E/AndroidRuntime(12169): at java.lang.reflect.Method.invoke(Method.java:511)
03-17 10:56:35.480: E/AndroidRuntime(12169): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
03-17 10:56:35.480: E/AndroidRuntime(12169): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
03-17 10:56:35.480: E/AndroidRuntime(12169): at dalvik.system.NativeStart.main(Native Method)
03-17 10:56:35.480: E/AndroidRuntime(12169): Caused by: java.lang.NullPointerException
03-17 10:56:35.480: E/AndroidRuntime(12169): at de.arvidg.exampleactionbartabs.UploadPicture.onCreate(UploadPicture.java:34)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.Activity.performCreate(Activity.java:5008)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
03-17 10:56:35.480: E/AndroidRuntime(12169): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
03-17 10:56:35.480: E/AndroidRuntime(12169): ... 11 more
main.xml中
<?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:layout_gravity="center"
android:orientation="vertical" >
<LinearLayout
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="@+id/selectpic"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="select Picture" />
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="225dp"
android:layout_weight="29.60"
android:src="@drawable/gradient_bg" />
<TextView
android:id="@+id/chosenpic"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="2.94"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
</LinearLayout>
</LinearLayout>
第34行是该声明的最后一个括号
buttonLoadImage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent i = new Intent(
Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(i, RESULT_LOAD_IMAGE);
}
});
答案 0 :(得分：2)
你的错误是我想到你面前。
您还提供了Button和ImageView的错误ID。
使用您在布局中指定的ID初始化按钮，如下所示：
将您的按钮ID定义为R.id.selectpic。
Button buttonLoadImage = (Button) findViewById(R.id.selectpic);
除了ImageView之外，您的R.id.imageView1 ID为R.id.chosenPicView，如下所示：
ImageView imageView = (ImageView) findViewById(R.id.imageView1);
然后试试。
答案 1 :(得分：1)
只需更改
Button buttonLoadImage = (Button) findViewById(R.id.choosepic2);
到
Button buttonLoadImage = (Button) findViewById(R.id.selectpic);
在您的代码中的某个时刻，您更改了布局文件中按钮的ID，并且没有反映活动代码的更改。
总是仔细检查您的ID。