從外部文件加載圖像時出錯

Question

因此，我試圖加載存儲在SD卡上的圖像並將其顯示在圖像視圖中。 但是，它會產生運行時錯誤。 這是我的Java代碼。

package com.example.cameracapture; 

import java.io.File; 

import android.support.v7.app.ActionBarActivity; 
import android.support.v4.app.Fragment; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.os.Bundle; 
import android.os.Environment; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
//import android.widget.Button; 
import android.widget.ImageView; 


public class DisplayPage extends ActionBarActivity { 

String path = Environment.getExternalStorageDirectory()+ "/DCIM/Camera/image_001.jpg"; 
File imgFile = new File(path); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_display_page); 

    if (savedInstanceState == null) { 
     getSupportFragmentManager().beginTransaction() 
       .add(R.id.container, new PlaceholderFragment()).commit(); 
    } 


    Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());     
    ImageView myImage = (ImageView) findViewById(R.id.Display); 
    myImage.setImageBitmap(myBitmap); 

} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 

    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.display_page, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 
    if (id == R.id.action_settings) { 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 

    public PlaceholderFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_display_page, container, 
       false); 
     return rootView; 
    } 
    } 
} 

這是我的XML文件

<?xml version="1.0" encoding="utf-8"?> 

<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/stupid_android" 
    android:layout_width="match_parent" 
    android:layout_height="400dp" 
    android:orientation="vertical" > 

    <ImageView 
     android:id="@+id/Display" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:contentDescription="@string/upload" /> 

    <View 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:background="#0000FF" /> 

</LinearLayout> 

我也知道這個錯誤是由於這些線 -

Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());     
    ImageView myImage = (ImageView) findViewById(R.id.Display); 
    myImage.setImageBitmap(myBitmap); 

因爲，當我刪除了上述三行代碼，空圖像視圖顯示完美。我是否稱錯了圖像？我應該怎麼做才能糾正它？也許我不應該在OnCreate方法中使用它？

編輯 - 這是我的錯誤日誌

06-10 12:47:02.796: E/AndroidRuntime(25074): FATAL EXCEPTION: main 
06-10 12:47:02.796: E/AndroidRuntime(25074): Process: com.example.cameracapture, PID: 25074 
06-10 12:47:02.796: E/AndroidRuntime(25074): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cameracapture/com.example.cameracapture.DisplayPage}: java.lang.NullPointerException 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread.access$800(ActivityThread.java:139) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.os.Handler.dispatchMessage(Handler.java:102) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.os.Looper.loop(Looper.java:136) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread.main(ActivityThread.java:5102) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at java.lang.reflect.Method.invokeNative(Native Method) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at java.lang.reflect.Method.invoke(Method.java:515) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at dalvik.system.NativeStart.main(Native Method) 
06-10 12:47:02.796: E/AndroidRuntime(25074): Caused by: java.lang.NullPointerException 
06-10 12:47:02.796: E/AndroidRuntime(25074): at com.example.cameracapture.DisplayPage.onCreate(DisplayPage.java:41) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.Activity.performCreate(Activity.java:5248) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110) 
06-10 12:47:02.796: E/AndroidRuntime(25074): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173) 
06-10 12:47:02.796: E/AndroidRuntime(25074): ... 11 more 

Answer 1

設置圖像中的onCreate是做正確的方式，但我的建議，因爲它是一個靜態圖像是使用drawable資源目錄和直接從XML設置圖像。

所以只需將您的圖像在相應的繪製目錄，然後添加到您的XML

<ImageView 
    android:id="@+id/Display" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:layout_weight="1" 
    android:contentDescription="@string/upload" 
    android:src="@drawable/image_001"/> 

<View 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:layout_weight="1" 
    android:background="#0000FF" /> 

一點題外話，你應該使用PNG圖像。

Answer 2

顯然，該錯誤是由於調用OnCreate方法中的圖像造成的。

我創建了一個新的方法，OnResume，並呼籲圖像出現，如下 -

@Override 
protected void onResume() { 
    super.onResume(); 
    String path = Environment.getExternalStorageDirectory()+ "/DCIM/Camera/image_001.jpg"; 
    File imgFile = new File(path); 

    Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());     
    ImageView myImage = (ImageView) findViewById(R.id.Display); 
    myImage.setImageBitmap(myBitmap); 
}