java - 使按钮在 Canvas 上绘制的新路径上可见

标签 java android android-canvas

我有一个 Canvas ，可以让用户绘制并允许他们保存然后共享。我遇到的问题是，一旦按下保存按钮，它就会被共享按钮取代。现在，如果用户不按共享，而是在现有图片上绘制新内容，我如何检查是否存在新路径，以便删除共享按钮并再次显示保存按钮？

XML:

<FrameLayout
    android:id="@+id/viewd"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="3"
    android:orientation="vertical"
    android:layout_gravity="center" >
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:padding="0dp"
        android:background="@drawable/bd"
        android:id="@+id/llFreeDraw" >
    </LinearLayout>
</FrameLayout>

我的绘图 Java 类:

package com.test.testing;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Paint.Style;
import android.view.MotionEvent;
import android.view.View;
import android.widget.TextView;

public class CustomView extends View {
    Paint paint;
    Path path;
    float x = 0;
    float y = 0;
    private int cWhite = Color.WHITE;

    public CustomView(Context context) {
        super(context);
        paint = new Paint();
        path= new Path();
        paint.setAlpha(255);
        paint.setColor(cWhite);
        paint.setStyle(Style.STROKE);
        paint.setStrokeWidth(20);
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(path,paint);
        canvas.drawCircle(x, y, 10, paint);
    }

    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        switch (action) {
        case MotionEvent.ACTION_DOWN:
            path.moveTo(event.getX(), event.getY());
            path.lineTo(event.getX(), event.getY());
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            x = event.getX();
            y = event.getY();
            path.lineTo(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            path.lineTo(event.getX(), event.getY());
            invalidate();
            break;
        case MotionEvent.ACTION_CANCEL:
            break;
        default:
            break;
        }
        return true;
    }
}

我的 MainActivity 类:

layout = (FrameLayout)findViewById(R.id.viewd);
        //layout.removeAllViews();
        view = new CustomView(FreeDraw.this);
        view.setLayoutParams(new FrameLayout.LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));
        layout.addView(view);
...
    View.OnClickListener saveHandle = new View.OnClickListener() {
        public void onClick(View v) {
            new SaveImageTask().execute(null, null, null);
        }
    };
    public class SaveImageTask extends AsyncTask<Void, Void, Void> {
         @Override
         protected Void doInBackground(Void... params) { //Running in background
            View content = layout;
            content.setDrawingCacheEnabled(true);
            content.setDrawingCacheQuality(View.DRAWING_CACHE_QUALITY_HIGH);
            Bitmap bitmap = content.getDrawingCache();
            File folder = new File(Environment.getExternalStorageDirectory() + "/PB");
            if (!folder.exists()) {
                folder.mkdir();
            }
            file = new File(folder + "/pb_image_" + Math.random()  + ".png");
            FileOutputStream ostream;
            try {
                file.createNewFile();
                ostream = new FileOutputStream(file);
                bitmap.compress(CompressFormat.PNG, 100, ostream);
                ostream.flush();
                ostream.close();
                isSaved = true;
            } catch (Exception e) {
                e.printStackTrace();
                isSaved = false;
            }
            return null;
         }

         @Override
         protected  void onPreExecute() { //Activity is on progress
             //displayToast("Your image is saving...");
             btnSave.setVisibility(View.GONE);
             btnShare.setVisibility(View.GONE);
             pb.setVisibility(View.VISIBLE);
         }

         @Override
         protected void onPostExecute(Void v) { //Activity is done...
            if (isSaved == true) {
                 displayToast("Image was saved.");
                 btnSave.setVisibility(View.GONE);
                 btnShare.setVisibility(View.VISIBLE);
                 pb.setVisibility(View.GONE);
             }
             if (isSaved == false) {
                 displayToast("Unable to save image. Try again later.");
                 btnSave.setVisibility(View.VISIBLE);
                 btnShare.setVisibility(View.GONE);
                 pb.setVisibility(View.GONE);
             }
         }
    }

如果绘制了新路径，如何显示“保存”按钮？

用图像画出我想做的事情...... enter image description here

我尝试将 Paint 类更改为:

package com.test.testing;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Paint.Style;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class CustomView extends View {
    Paint paint;
    Path path;
    float x = 0;
    float y = 0;
    private int cWhite = Color.WHITE;
    private Button btnS, btnSa;

    public CustomView(Context context) {
        super(context);
        paint = new Paint();
        path= new Path();
        paint.setAlpha(255);
        paint.setColor(cWhite);
        paint.setStyle(Style.STROKE);
        paint.setStrokeWidth(20);

        btnS = (Button) findViewById(R.id.shareButton);
        btnSa = (Button) findViewById(R.id.saveButton);
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(path,paint);
        canvas.drawCircle(x, y, 10, paint);
    }

    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        switch (action) {
        case MotionEvent.ACTION_DOWN:
            path.moveTo(event.getX(), event.getY());
            path.lineTo(event.getX(), event.getY());
            if (btnS.getVisibility() == View.VISIBLE && btnS != null) {
                btnS.setVisibility(View.GONE);
                btnSa.setVisibility(View.VISIBLE);
            }
            else {
                //do nothing...
            }
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            x = event.getX();
            y = event.getY();
            path.lineTo(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            path.lineTo(event.getX(), event.getY());
            invalidate();
            break;
        case MotionEvent.ACTION_CANCEL:
            break;
        default:
            break;
        }
        return true;
    }
}

在我的 ACTION_DOWN 事件中添加了以下行，以隐藏“共享”按钮并显示“保存”按钮:

    if (btnS.getVisibility() == View.VISIBLE && btnS != null) {
        btnS.setVisibility(View.GONE);
        btnSa.setVisibility(View.VISIBLE);
    }
    else {
        //do nothing...
    }

但是我收到一个错误，我的 LogCat:

09-04 21:35:58.752: E/AndroidRuntime(3835): FATAL EXCEPTION: main
09-04 21:35:58.752: E/AndroidRuntime(3835): java.lang.NullPointerException
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.test.testing.CustomView.onTouchEvent(CustomView.java:47)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.View.dispatchTouchEvent(View.java:7246)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1875)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1875)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1875)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1875)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1875)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1953)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1405)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.app.Activity.dispatchTouchEvent(Activity.java:2410)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1901)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.View.dispatchPointerEvent(View.java:7426)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3220)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3165)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4292)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4271)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4363)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:179)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.os.MessageQueue.nativePollOnce(Native Method)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.os.MessageQueue.next(MessageQueue.java:125)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.os.Looper.loop(Looper.java:124)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at android.app.ActivityThread.main(ActivityThread.java:5195)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at java.lang.reflect.Method.invokeNative(Native Method)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at java.lang.reflect.Method.invoke(Method.java:511)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
09-04 21:35:58.752: E/AndroidRuntime(3835):     at dalvik.system.NativeStart.main(Native Method)

有什么建议如何修复它或如何完成该步骤吗？

最佳答案

您会收到 NullPointerException，因为在 onTouchEvent() 方法中按钮引用为 null。发生这种情况是因为您直接使用 findViewById() 查找按钮，该按钮仅在自定义 View 及其 subview 中查找按钮。所以，而不是:

btnS = (Button) findViewById(R.id.shareButton);
btnSa = (Button) findViewById(R.id.saveButton);

在包含按钮和自定义 View 的 Activity(构造函数中传递的 Context 参数)中查找按钮:

btnS = (Button)((Activity) context).findViewById(R.id.shareButton);
btnSa = (Button)((Activity) context).findViewById(R.id.saveButton);.

关于java - 使按钮在 Canvas 上绘制的新路径上可见，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18626487/

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