Extending a EditText in Android. What am I doing w

问题:

So I'm trying to get a grasp of using custom controls in Android. But my app crashes on trying to create the activity. Here's the code:

package com.myApp;
import android.content.Context;
import android.widget.EditText;
import android.view.View;
import android.view.View.OnClickListener;

public class MyEditText extends EditText implements OnClickListener {

    public MyEditText(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }   
    public void FlashBorder()
    {
        //do some custom action
    }
    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        EditText txt = (EditText) v;
        txt.selectAll();
    }
}

Here's the layout xml:

<com.myApp.MyEditText
     android:id="@+id/edtTaskName"
     android:layout_height="wrap_content"
     android:layout_width="match_parent"/> 

回答1:

You will need to implement these constructors:

public class TestEditText extends EditText {
    public TestEditText(Context context) {
        super(context);
    }

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

    public TestEditText(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public TestEditText(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }
}

for example try to do the following :

public TestEditText(Context context, AttributeSet attrs) {
    super(context, attrs);
    Log.i("attribute name at index 0", attrs.getAttributeName(0));
}

you will get the following in your logcat :

attribute name at index 0 = id 

so to deliver these XML attributes to the Super class (EditText) you have to override these constructors.

Hope that Helps.

回答2:

You have to add this constructor for creating any custom View.

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

instead of

public MyEditText(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }  

回答3:

import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Typeface;
import android.os.Build;
import android.util.AttributeSet;




/**
 * Created by rohann on 14/07/2016.
 */
public class LightEditText extends android.widget.EditText{

    public LightEditText(Context context) {
        super(context);
        setFont();

    }

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

    public LightEditText(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setFont();
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public LightEditText(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        setFont();
    }

    /**
     * This method is used to set the given font to the TextView.
     */
    private void setFont() {
        Typeface typeface = TypefaceCache.get(getContext().getAssets(), "fonts/Roboto-Light.ttf");
        setTypeface(typeface);
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
    }
}