扩展TextView没有出现

Question

以下代码假设是这样做的：
- 使用标准TextView显示字符串
- 使用扩展TextView显示字符串。 （这个覆盖了OnDraw并在字符串中画了一条线，使它看起来像被删除了）

问题是只出现了标准版本。

请检查以下代码：

ExpenseWatchActivity.java（这是主要活动）

package com.app.expensewatch;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import java.util.Calendar;

public class ExpenseWatchActivity extends Activity {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        int day,mon,yr;

        Calendar cal = Calendar.getInstance();

        day = cal.get(Calendar.DATE);
        mon = 1 + cal.get(Calendar.MONTH);
        yr = cal.get(Calendar.YEAR);

        String text = getResources().getString(R.string.hello, day , mon , yr);

        TextView tx1 = (TextView)findViewById(R.id.text1);
        tx1.setText(text);

        List1 list = (List1)findViewById(R.id.list1);
        list.setText(text);
    }
}

List1.java（这是扩展的TextView）

package com.app.expensewatch;

import android.util.AttributeSet;
import android.widget.TextView;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import com.app.expensewatch.R;

public class List1 extends TextView {

    public List1(Context context) {
        super(context);
    }

    public List1(Context context, AttributeSet attrs) {
        super( context, attrs );
    }

    public List1(Context context, AttributeSet attrs, int defStyle) {
        super( context, attrs, defStyle );
    }

    float ht = (float)getHeight();
    float wd = (float)getWidth();

    @Override
    protected void onDraw(Canvas canvas)
    {
        Paint divider = new Paint();
        divider.setColor(getResources().getColor(R.color.line1));
        canvas.drawLine(0,ht/2,wd,ht/2,divider);
    }
}

main.xml中

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/text1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

    <com.app.expensewatch.List1
        android:id="@+id/list1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello" />
       />
 </LinearLayout>

的strings.xml

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

   <string name="app_name">ExpenseWatch</string>
   <string name="hello">Today is : %1$d / %2$d / %3$d</string>

</resources>

colors.xml

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

    <color name="line1">#6456648f</color>

</resources>

Answer 1

在扩展TextView中设置宽度和高度时，尚未测量视图。它的宽度和高度为零。在扩展的TextView中覆盖onMeasure（），并在那里设置宽度和高度。

protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    ht = getHeight();
    wd = getWidth();    
}

在调用onMeasure（）之后，始终避免设置将在视图中保存维度的私有变量。