java - "Unfortunately app has stopped"错误？

Question

我正在尝试为 android 编写一个基本的绘图 Android 应用程序并在 Genymotion 上测试它，但我无法单击应用程序图标(它显示“不幸的是 [app] 已停止。”)

我不确定这三个私有(private)变量是否应该位于MainActivity类下？或者它与我的 AndroidManifest.xml 文件有关。有人可以看一下我的代码吗？

我的 MainActivity.java 文件:

package edu.berkeley.cs160.opalkale.prog2;

import android.os.Bundle;
import android.app.Activity;
import android.graphics.Paint;
import android.view.Menu;
import android.view.View;
import android.widget.ImageButton;
import android.widget.LinearLayout;

public class MainActivity extends Activity {
private Paint myPaint;
private ImageButton currPaint;
private myView drawView;

public void paintClicked(View view) {
    if (view != currPaint) {
        // update color
        ImageButton imgView = (ImageButton) view;
        String color = view.getTag().toString();

        drawView.setColor(color);
        imgView.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
        currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint));
        currPaint = (ImageButton)view;
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    myView mV = new myView(this, null);
    setContentView(mV);

    drawView = (myView) findViewById(R.id.drawing);

    LinearLayout paintLayout = (LinearLayout) findViewById(R.id.paint_colors);
    currPaint = (ImageButton) paintLayout.getChildAt(0);
    currPaint.setImageDrawable(getResources().getDrawable(
            R.drawable.paint_pressed));
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

<小时/>

我的 AndroidManifest.xml 文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="edu.berkeley.cs160.opalkale.prog2"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="13"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="edu.berkeley.cs160.opalkale.prog2.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

<小时/>

日志猫:

[2014-02-11 23:04:43 - DeviceMonitor] Adb connection Error:EOF
[2014-02-11 23:04:43 - DeviceMonitor] Sending jdwp tracking request failed!
[2014-02-11 23:04:43 - DeviceMonitor] Connection attempts: 1
[2014-02-11 23:04:44 - DeviceMonitor] Connection attempts: 2
[2014-02-11 23:04:45 - DeviceMonitor] Connection attempts: 3
[2014-02-11 23:04:46 - DeviceMonitor] Connection attempts: 4
[2014-02-11 23:04:47 - DeviceMonitor] Connection attempts: 5
[2014-02-11 23:04:48 - DeviceMonitor] Connection attempts: 6
[2014-02-11 23:04:49 - DeviceMonitor] Connection attempts: 7
[2014-02-11 23:04:50 - DeviceMonitor] Connection attempts: 8
[2014-02-11 23:04:51 - DeviceMonitor] Connection attempts: 9
[2014-02-11 23:04:52 - DeviceMonitor] Connection attempts: 10
[2014-02-11 23:04:53 - DeviceMonitor] Connection attempts: 11
[2014-02-11 23:07:14 - Logcat] device not found
com.android.ddmlib.AdbCommandRejectedException: device not found
at com.android.ddmlib.AdbHelper.setDevice(AdbHelper.java:774)
at com.android.ddmlib.AdbHelper.executeRemoteCommand(AdbHelper.java:396)
at com.android.ddmlib.AdbHelper.executeRemoteCommand(AdbHelper.java:347)
at com.android.ddmlib.Device.executeShellCommand(Device.java:444)
at com.android.ddmuilib.logcat.LogPanel$3.run(LogPanel.java:531)

<小时/>

activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:screenOrientation="portrait"
tools:context=".MainActivity" >

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FFCCCCCC"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="50dp"
        android:layout_gravity="center"
        android:orientation="horizontal" >

        <ImageButton
            android:id="@+id/new_btn"
            android:layout_width="wrap_content"
            android:layout_height="fill_parent"
            android:contentDescription="@string/brush"
            android:src="@drawable/brush" />
    </LinearLayout>

    <edu.berkeley.cs160.opalkale.prog2.myView
        android:id="@+id/drawing"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="3dp"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"
        android:layout_marginTop="3dp"
        android:layout_weight="1"
        android:background="#FFFFFFFF" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:orientation="vertical" >

        <LinearLayout
            android:id="@+id/paint_colors"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal" >

            <ImageButton
                android:layout_width="@dimen/large_brush"
                android:layout_height="@dimen/large_brush"
                android:layout_margin="2dp"
                android:background="#FF787878"
                android:contentDescription="@string/paint"
                android:onClick="paintClicked"
                android:src="@drawable/paint"
                android:tag="#FF787878" />
        </LinearLayout>

        </LinearLayout>
    </LinearLayout>

</RelativeLayout>

<小时/>

myView 类:

package edu.berkeley.cs160.opalkale.prog2;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class myView extends View {
private Path drawPath;
private Paint drawPaint, canvasPaint;
private int paintColor = 0xFF787878;
private Canvas drawCanvas;
private Bitmap canvasBitmap;

public void setColor(String newColor){
    //set color     
    invalidate();
    paintColor = Color.parseColor(newColor);
    drawPaint.setColor(paintColor); 
    }

public myView(Context context, AttributeSet attrs) {
    super(context, attrs);

    setupDrawing();
}

private void setupDrawing() {
    drawPath = new Path();
    drawPaint = new Paint();
    drawPaint.setColor(paintColor);
    drawPaint.setAntiAlias(true);
    drawPaint.setStrokeWidth(20);
    drawPaint.setStyle(Paint.Style.STROKE);
    drawPaint.setStrokeJoin(Paint.Join.ROUND);
    drawPaint.setStrokeCap(Paint.Cap.ROUND);

    canvasPaint = new Paint(Paint.DITHER_FLAG);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    // view given size
    super.onSizeChanged(w, h, oldw, oldh);
    canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    drawCanvas = new Canvas(canvasBitmap);
}

@Override
protected void onDraw(Canvas canvas) {
    // draw view
    canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
    canvas.drawPath(drawPath, drawPaint);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    // detect user touch
    float touchX = event.getX();
    float touchY = event.getY();

    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
        drawPath.moveTo(touchX, touchY);
        break;
    case MotionEvent.ACTION_MOVE:
        drawPath.lineTo(touchX, touchY);
        break;
    case MotionEvent.ACTION_UP:
        drawCanvas.drawPath(drawPath, drawPaint);
        drawPath.reset();
        break;
    default:
        return false;
    }
    invalidate();
    return true;
}

}

Answer 1

您的代码中缺少

setContentView(Id);。因此它会给您 NullPointerException

为您的 Activity 设置一些 View ，例如

setContentView(R.layout.layout);