无法在布局中实现drawView

Question

我使用3行创建一个三角形，我使用的是drawView。它出来很好。但重点是我正在将setContentView作为setContentView（drawView）而不是setContentView（R.layout.xml）。结果我看不到xml中的文本框和按钮。我知道我必须在我的布局中创建一个DrawView实例，然后执行setContentView（R.layout.xml）。我试过这样做，但我仍然收到错误。

请帮忙！

我的xml代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="horizontal">


    <com.example.testapp.DrawView
    android:id="@+id/draw_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />


    <EditText android:id="@+id/edit_message"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="@string/edit_message" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_send" 
        android:onClick="sendMessage" />
</LinearLayout>

我的活动代码

package com.example.testapp;



import android.content.Context;
import android.content.Intent;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;



public class MainActivity extends ActionBarActivity {
    public final static String EXTRA_MESSAGE = "com.example.testapp.MESSAGE";


    DrawView drawView;

    protected void onCreate(Bundle savedInstanceState) {
         System.out.println(" ONCREATE+++");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //drawView = (DrawView)findViewById(R.id.draw_view);
    }

    @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;
    }

    @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);
    }
    public void sendMessage(View view) {
        Intent intent = new Intent(this, DisplayMessageActivity.class);
        EditText editText = (EditText) findViewById(R.id.edit_message);
        String message = editText.getText().toString();
        intent.putExtra(EXTRA_MESSAGE, message);
        startActivity(intent);
    }

class DrawView extends View {

        Paint paint1 = new Paint();
        Paint paint2 = new Paint();
        Paint paint3 = new Paint();


        public DrawView(Context context) {
            super(context);
            System.out.println(" DrawView1");
            paint1.setColor(Color.RED);
            paint2.setColor(Color.BLUE);
            paint3.setColor(Color.GREEN);
            System.out.println(" DrawView2");
        }

        @Override
        public void onDraw(Canvas canvas) {
             super.onDraw(canvas);
             System.out.println(" onDraw");
                canvas.drawLine(150, 640, 550, 300, paint1); // Slant Line
                canvas.drawLine(150, 640, 550, 640, paint2); // Horizontal Line
                canvas.drawLine(550, 300, 550, 640, paint3); // Vertical Line
                canvas.drawCircle(150, 655, 15, paint2);// Circle for roller support

                canvas.drawLine(550, 640, 565, 655, paint2); // Line1 for hinge support
                canvas.drawLine(550, 640, 535, 655, paint3); // Line 2 for hinge support

               // canvas.drawRect(535, 625, 555, 665, paint2); //Rectangle depicting Hinge Support
                canvas.drawLine(660, 300, 550, 300, paint2);// Load Length
                canvas.drawLine(550/*Start*/, 300, 565, 280, paint2); // Load Arm1
                canvas.drawLine(550, 300, 565, 320, paint2); // Load Arm2
        }
}
}

谢谢！