我正在尝试将一个onTouchListener添加到ImageView，以便我可以从他们拍摄的图像中获取用户选择的像素值。因此，我在我的主要活动中实现了onTouchListener，并将其用作ImageView imageview的onTouchListener。
我的代码如下：
package com.andrew.omnidropper;
import java.io.File;
import java.net.URI;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
public class OmniDropperActivity extends Activity implements OnTouchListener {
protected static final int TAKE_PICTURE_INTENT = 0;
protected static final int SELECT_PREVIOUS_PHOTO_INTENT = 1;
/** Called when the activity is first created. */
public Button cameraButton;
public ImageView imageview;
public ImageView colordisplay;
private Bitmap bitmap;
private Uri imageUri;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
cameraButton = (Button) findViewById(R.id.camerabutton);
imageview = (ImageView) findViewById(R.id.imageview);
colordisplay = (ImageView) findViewById(R.id.colordisplay);
cameraButton.setOnClickListener(clickListener);
imageview.setOnTouchListener(this);
}
OnClickListener clickListener = new OnClickListener() {
public void onClick(View v) {
if(v.getId() == R.id.camerabutton){
Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
File photo = new File(Environment.getExternalStorageDirectory(), "Pic.jpg");
intent.putExtra(MediaStore.EXTRA_OUTPUT,
Uri.fromFile(photo));
imageUri = Uri.fromFile(photo);
startActivityForResult(intent, 0);
setContentView(R.layout.selectcolorspot);
}
/*if(v.getId() == R.id.imagebutton){
Intent intent = new Intent();
intent.setType("image/*");
intent.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent, "Select Picture"),
SELECT_PREVIOUS_PHOTO_INTENT);
setContentView(R.layout.selectcolorspot);
}(*/
/*if(v.getId() == R.id.scratchbutton){
setContentView(R.layout.makenewcolor);
}*/
}
};
private int colorPicked;
public void onActivityResult(int requestCode, int resultCode, Intent data){
super.onActivityResult(requestCode, resultCode, data);
switch (requestCode) {
case 0:
if (resultCode == Activity.RESULT_OK) {
Uri selectedImage = imageUri;
getContentResolver().notifyChange(selectedImage, null);
imageview = (ImageView) findViewById(R.id.imageview);
ContentResolver cr = getContentResolver();
try {
bitmap = android.provider.MediaStore.Images.Media
.getBitmap(cr, selectedImage);
imageview.setImageBitmap(bitmap);
imageview.setScaleType(ImageView.ScaleType.FIT_XY);
Toast.makeText(this, "Select an point on the image and press OK",
Toast.LENGTH_LONG).show();
} catch (Exception e) {
Toast.makeText(this, "Failed to load", Toast.LENGTH_SHORT)
.show();
Log.e("Camera", e.toString());
}
}
}
}
public boolean onTouch(View v, MotionEvent e) {
if(v.getId() == R.id.imageview){
if(e.getAction() == MotionEvent.ACTION_DOWN && bitmap != null){
colorPicked = bitmap.getPixel((int) e.getX(),(int) e.getY());
setContentView(R.layout.iscolorok);
colordisplay.setBackgroundColor(colorPicked);
}
}
return false;
}
}
但是当我尝试运行它时，它会崩溃。
这是logcat输出：
03-28 20:43:54.613: D/AndroidRuntime(4761): Shutting down VM
03-28 20:43:54.613: W/dalvikvm(4761): threadid=1: thread exiting with uncaught exception (group=0x40018560)
03-28 20:43:54.621: E/AndroidRuntime(4761): FATAL EXCEPTION: main
03-28 20:43:54.621: E/AndroidRuntime(4761): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.andrew.omnidropper/com.andrew.omnidropper.OmniDropperActivity}: java.lang.NullPointerException
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1696)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1716)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread.access$1500(ActivityThread.java:124)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:968)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.os.Handler.dispatchMessage(Handler.java:99)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.os.Looper.loop(Looper.java:123)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread.main(ActivityThread.java:3806)
03-28 20:43:54.621: E/AndroidRuntime(4761): at java.lang.reflect.Method.invokeNative(Native Method)
03-28 20:43:54.621: E/AndroidRuntime(4761): at java.lang.reflect.Method.invoke(Method.java:507)
03-28 20:43:54.621: E/AndroidRuntime(4761): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-28 20:43:54.621: E/AndroidRuntime(4761): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-28 20:43:54.621: E/AndroidRuntime(4761): at dalvik.system.NativeStart.main(Native Method)
03-28 20:43:54.621: E/AndroidRuntime(4761): Caused by: java.lang.NullPointerException
03-28 20:43:54.621: E/AndroidRuntime(4761): at com.andrew.omnidropper.OmniDropperActivity.onCreate(OmniDropperActivity.java:47)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-28 20:43:54.621: E/AndroidRuntime(4761): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1660)
03-28 20:43:54.621: E/AndroidRuntime(4761): ... 11 more
03-28 20:43:59.519: I/Process(4761): Sending signal. PID: 4761 SIG: 9
我不认为imageview是null因为我声明它，所以为什么会抛出nullPointerException？
答案 0 :(得分：4)
您的imageview可能为null。如果找不到视图，findViewById方法将返回null。您确定在main布局中定义了您要提取的ImageView吗？我将使用调试器逐步完成它，看看imageview是否为空。