Android從Gallery NullPointerException中挑選圖像？

Question

我目前正在嘗試創建一個應用程序，該應用程序允許用戶從圖庫中查找圖像並將其上傳到服務器。但我仍然堅持挑選一個形象。 我完全按照教程，但啓動活動時，我得到一個NullPointer。

你們看到有什麼錯誤嗎？

在此先感謝！

繼承人的代碼;

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)); 

     } 


    } 
} 

的logcat：

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 

的main.xml 34

<?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> 

線是該聲明的最後一個支架

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); 
      } 
     }); 

Answer 1

只是改變

Button buttonLoadImage = (Button) findViewById(R.id.choosepic2); 

到

Button buttonLoadImage = (Button) findViewById(R.id.selectpic); 

在代碼中的某個時候，你已經改變了按鈕的ID在佈局文件中並沒有體現在活動代碼變化。

總是仔細檢查您的ID。

Answer 2

你的錯誤是我THI nk在你面前。 您也給出了Button和ImageView的錯誤標識。

使用您在佈局中給出的ID初始化您的按鈕，如下所示： 將您的按鈕ID定義爲R.id.selectpic。

Button buttonLoadImage = (Button) findViewById(R.id.selectpic); 

而且你ImageView ID作爲R.id.imageView1如下除了R.id.chosenPicView：

ImageView imageView = (ImageView) findViewById(R.id.imageView1); 

然後再嘗試。